What Is Prokaryote?

Prokaryotes are mostly unicellular organisms without a nucleus, in contrast to eukaryotes, organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between prokaryote and eukaryote cell structure is the most important in the living world. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. However, Woese has proposed dividing them into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) on the supposition that these have separate origins. This controversial arrangement is called the three-domain system.

Prokaryotes do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime layer secreted by the cells. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of the human body.

The name prokaryote comes from the Greek pros meaning before and karyon meaning nut, referring to the nucleus. Prokaryotes also lack cytoskeletons and membrane-bound cell compartments such as vacuoles, endoplasmic reticulum, mitochondria and chloroplasts. In eukaryotes, the latter perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur within the cell membrane, and endosymbionts are extremely rare. They are usually much smaller than eukaryotic cells.

Prokaryotes have a single chromosome, contained within a nucleoid region rather than a membrane-bound nucleus, but may also have various small circular pieces of DNA called plasmids spread throughout the cell. Reproduction is exclusively asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.

Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. They include the animals, plants, and fungi, which are mostly multicellular, as well as various other groups called protists, many of which are unicellular. In contrast, other organisms such as bacteria lack nuclei and other complex cell structures, and are called prokaryotes. The eukaryotes share a common origin, and are often treated formally as a superkingdom, empire, or domain. The name comes from the Greek eus or true and karyon or nut, referring to the nucleus.

It is generally accepted that the first living cells were some form of prokaryote, and they are known as fossils from over 3.5 billion years ago. Some have suggested structures within a Martian meteorite should be interpreted as fossil prokaryotes, but this is extremely doubtful.

After the first prokaryotes evolved, they subsequently have had an explosion of diversification during the ages. The metabolism of prokaryotes is the most diverged and cause some prokaryotes to be very different from each other.

The prokaryotes consist of millions of genetically-distinct unicellular organisms. What they lack in structural diversity, so well-known among eukaryotes (including the protista), they make up for in their physiological diversity. It is often a particular physiological trait that unifies and distinguishes a particular group of prokaryotes to microbiologists. In Bergey's Manual of Determinative Bacteriology (1994), the identifiable groups of prokaryotes are assembled based on easily-observed phenotypic characteristics such as Gram stain, morphology (rods, cocci, etc), motility, structural features (e.g. spores, filaments, sheaths, appendages, etc.), and on distinguishing physiological features (e.g. anoxygenic photosynthesis, anaerobiasis, methanogenesis, lithotrophy, etc.).

The Archaea are not eukaryotes, which makes them prokaryotes. However, the fact that they are related to Eucarya, not to the other prokaryotic organisms (the Bacteria), means that prokaryotes are not a natural group. This is difficult to fully appreciate, since we tend to accord a special status to eukaryotic cells. It is perhaps most easily understood by considering the ability to learn about one group from another:

If we wonder about a biosynthetic reaction in a eukaryote, it makes more sense to use a member of the Archaea as a model than to use a member of the Bacteria. Even though much more money is being spent on analysis of eukaryotic genomes than prokaryotic genomes, due to their smaller size, some prokaryotic genomes will be completed first. Of these, it appears that we will learn more about human genes from the archaeal genomes than from the bacterial genomes.

If we wonder about transcription initiation in Thermococcus celer (an archaeon), should we look at what is known about transcription in E. coli (another prokaryote) or in yeast (a eukaryote)? It is now known that the transcription apparatus of T. celer seems to be much more similar to that of yeast than to that of E. coli.

Prokaryotic cells may have photosynthetic pigments, such as is found in cyanobacteria ("blue bacteria"). Some prokaryotic cells have external whip-like flagella for locomotion or hair like pili for adhesion. Prokaryotic cells come in multiple shapes: cocci (round), baccilli (rods), and spirilla or spirochetes (helical cells).

There are three domains of life that have or had a prokaryotic grade of organisation:

Archaea (Archaeobacteria, which have an anaerobic metabolism), Eubacteria ("true" bacterial and blue-green algae), and the hypothetical Urkaryote organism (which, it is believed, enetered into a symbiotic relationship with several different prokaryote species to form the first eukaryote cell

Prokaryotes are unicellular organisms, found in all environments. Prokaryotes are the largest group of organisms, mostly due to the vast array of bacteria which comprise the bulk of the prokaryote classification. Characteristics:

No nuclear membrane (genetic material dispersed throughout cytoplasm) No membrane-bound organelles Simple internal structure Most primitive type of cell (appeared about four billion years ago) Examples:

Staphylococcus Escherichia coli (E. coli) Streptococcus

In the world of cells, there are two major groups: the prokaryotes and the eukaryotes. They are very similar in that they contain many of the same parts. However, there are a few major differences between them.

Eukaryotes contain membrane-bound nuclei and other organelles, while prokaryotes lack this membrane-bound nucleus. Prokaryotes are classified in two kingdoms separate from the eukaryotes. Eukaryotes are the type of cells that make up plants and one celled organisms, but not animals.

The reason that they have a membrane-bound nucleus is because they have to carry out all the processes of life, which is untrue in prokaryotes. Prokaryotes rely on many cells working together to function. While eukaryotes are radically different from one another, they do have three general parts that allow them to carry out these processes of life. These are the cell membrane, the nucleus, and other organelles. The organelles are very important to the cell’s functioning.

Some of these organelles include mitochondria, which transfer energy from organic compounds to ATP. The ribosomes organize the synthesis of proteins (which is used to get energy). The rough endoplasmic reticulum prepares proteins for export. The smooth endoplasmic reticulum regulates calcium levels, breaks down toxic substances, and synthesizes steroids. The golgi body processes and packages substances produced by the cell. The lysosomes digest molecules.

There are other little parts to the cells which aid in all of this. These include microfilaments, cilia, flagella (those two assist in transportation), and of course the nucleus. In a plant, there are also the cell wall, the vacuole, and the plastid. All of these organelles are used to carry out the life processes.

Prokaryotes and Eucaryotes:

The Cell Membrane encloses the cell. Water and nutrients are admitted through the cell wall, and wastes are expelled. Bacteria and plant cells also have a protective cell wall, but animals have a membrane without a wall.

Cytoplasm is the watery stuff that fills the cell, provides a medium in which to move the molecules around. The cytoplasm is full of chemicals: dissolved oxygen and / or carbon dioxide, amino acids, simple sugars, molecules of carbohydrates, proteins, or lipids (fats). More than half of the cell contents is water.

In eukaryotes the inside of the cell is full of membranes that guide and contain and compartmentalize the cell contents.

Ribosomes do protein synthesis. I think of them as being like workers in a fast food place. When the cell needs proteins, the ribosomes get information about how to make the proteins by copying a piece of the DNA. That is like taking the order.

The proteins are made of amino acids, which are floating in the cytoplasm. The ribosome collects the amino acids which fill the order. It puts the amino acids together correctly. That is like assembling and packing up the items on the order.

When the order is complete, the protein folds up and is ready to use. The folding up is the customer's smile!

Prokaryota means "before a nucleus".

Prokaryotes are single-celled organisms. They are the smallest, simplest organisms.

The group includes bacteria (or eubacteria) and archaea.

They are abundant in the air, water, soil, and on most objects.

Prokaryotes are small (0.5 - 1.5 microns).

A plasma membrane surrounds the cell.

Prokaryotes have no membrane-bound organelles such as a nucleus, mitochondria, chloroplasts, golgi apparatus, or endoplasmic reticulum.

Many enzymes such as those needed in cellular respiration are attached to the plasma membrane. In eukaryotes, the enzymes needed for cellular respiration are located within the mitochondrion.

Photosynthetic forms do have membraneous vesicles where photosynthetic pigments (chlorophyll) are located. These structures are called thylakoids.

Ribosomes are the only cytoplasmic organelles. They are smaller than eukaryote ribosomes.

The nucleoid is a region where the circular chromosome (DNA) is located.

Plasmids are accessory rings of DNA. Some biotechnology techniques involve the use of plasmids as vectors to insert foreign DNA into the bacteria. For example, human genes are inserted into bacteria by first splicing them into a plasmid. The plasmid is then taken up by a bacterium.

They usually have a cell wall. It prevents bursting or shrinking when the osmotic concentration changes.

The cell is surrounded by a capsule (attached) and/or by a loose gelatinous sheath (slime layer).

Some move by means of flagella. The flagellum contains a hook and a basal body. It rotates 360° to propel the cell.

Many adhere to surfaces by short hair-like structures called fimbriae.

Prokaryotes are very small cells that have no membrane around their nucleus nor any organelles. Prokaryotes include bacteria. They are the simplest organisms on Earth, and also the commonest. Every part of your skin is smothered in them. Their spores fill the air we breathe. Every glass of water we drink, even good clean drinking water, contains millions of them. On the outside they have a strong cell wall. Beneath this is a membrane which will allow oily molecules to pass but prevents electrically charged molecules, and free protons and electrons, from passing through. Beneath this is a watery space full of molecules and ribosomes, messenger nucleic acids and all the other things needed to keep life going, all mixed up in a mostly chaotic way. There are some organelles within the cell, which function as storage compartments, but these do not have a membrane surrounding them as they do in eukaryotes. Instead they are surrounded by a protein coat.

At the center of the prokaryote is the nuclear region, but not separated from the rest of the cell by a membrane. This contains the DNA of the prokaryote, which is a long strand with its ends fixed together. The prokaryote may also contain shorter sequences of DNA called plasmids. These can move from one cell to another and carry information how to make proteins which inactivate antibiotics, for example.

At one end of the prokaryote there may be a wonderful little motor with a long stiff strand attached to it on the outside of the cell. As the motor rotates this strand is twirled around and pushes the cell along. So some prokaryotes can swim! The rod is called a flagellum or 'whip'.

In times of hardship, prokaryotes can shut down most of their life processes and wrap themselves up in a very hard outer coating.

Procaryotes are unicellular organisms of relatively simple construction, especially if compared to eukaryotes. Whereas eukaryotic cells have a preponderance of organelles with separate cellular functions, procaryotes carry out all cellular functions as individual units. A procaryotic cell has five essential structural components: a genome (DNA), ribosomes, cell membrane, cell wall, and some sort of surface layer which may or may not be an inherent part of the wall. Other than enzymatic reactions, all the cellular reactions incidental to life can be traced back to the activities of these macromolecular structural components. Thus, functional aspects of procaryotic cells are related directly to the structure and organization of the macromolecules in their cell make-up, i.e., DNA, RNA, phospholipds, proteins and polysaccharides. Diversity within the primary structure of these molecules accounts for the diversity that exists among procaryotes.

At one time it was thought that bacteria were essentially "bags of enzymes" with no inherent cellular architecture. The development of the electron microscope, in the 1950s, revealed the distinct anatomical features of bacteria and confirmed the suspicion that they lacked a nuclear membrane. Structurally, a procaryotic cell (Figure 1 below) has three architectural regions: appendages (attachments to the cell surface) in the form of flagella and pili (or fimbriae); a cell envelope consisting of a capsule, cell wall and plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. In this chapter, we will discuss the anatomical structures of procaryotic cells in relation to their adaptation, function and behavior in natural environments.

Most procaryotes have a rigid cell wall. The cell wall is an essential structure that protects the cell protoplast from mechanical damage and from osmotic rupture or lysis. Procaryotes usually live in relatively dilute environments such that the accumulation of solutes inside the procaryotic cell cytoplasm greatly exceeds the total solute concentration in the outside environment. Thus, the osmotic pressure against the inside of the plasma membrane may be the equivalent of 10-25 atm. Since the membrane is a delicate, plastic structure, it must be restrained by an outside wall made of porous, rigid material that has high tensile strength. Such a material is murein, the ubiquitous component of bacterial cell walls.

The cell walls of bacteria deserve special attention for several reasons: 1. They are an essential structure for viability, as described above. 2. They are composed of unique components found nowhere else in nature. 3. They are one of the most important sites for attack by antibiotics. 4. They provide ligands for adherence and receptor sites for drugs or viruses. 5. They cause symptoms of disease in animals. 6. They provide for immunological distinction and immunological variation among strains of bacteria.

The cell walls of all Bacteria contain a unique type of peptidoglycan called murein. Peptidoglycan is a polymer of disaccharides (a glycan) cross-linked by short chains of amino acids (peptides), and many types of peptidoglycan exist. All Bacterial peptidoglycans contain N-acetylmuramic acid, which is the definitive component of murein. The cell walls of Archaea may be composed of protein, polysaccharides, or peptidoglycan-like molecules, but never do they contain murein. This feature distinguishes the Bacteria from the Archaea.

The cytoplasmic constituents of procaryotic cells invariably include the procaryotic chromosome and ribosomes. The chromosome is typically one large circular molecule of DNA, more or less free in the cytoplasm. Procaryotes sometimes possess smaller extrachromosomal pieces of DNA called plasmids. The total DNA content of a procaryote is referred to as the cell genome. During cell growth and division, the procaryotic chromosome is replicated in the usual semi-conservative fashion before for distribution to progeny cells. However, the eukaryotic processes of meiosis and mitosis are absent in procaryotes. Replication and segregation of procaryotic DNA is coordinated by the membrane, possibly by mesosomes.

The distinct granular appearance of procaryotic cytoplasm is due to the presence and distribution of ribosomes The ribosomes of procaryotes are smaller than cytoplasmic ribosomes of eukaryotes. procaryotic ribosomes are 70S in size, being composed of 30S and 50S subunits. The 80S ribosomes of eukaryotes are made up of 40S and 60S subunits. Ribosomes are involved in the process of translation (protein synthesis), but some details of their activities differ in eukaryotes, Bacteria and Archaea. Protein synthesis using 70S ribosomes occurs in eukaryotic mitochondria and chloroplasts, and this is taken as a major line of evidence that these organelles are descended from procaryotes.

The two major kinds of cells are prokaryotic cells and eukaryotic cells. The prokaryotic cell is the simplest of the two cell types. Prokaryotes have no true nucleus (Greek pro = before, karyon = kernel (nucleus)). Instead, their genetic material is found as circular DNA in the nucleoid region with no nuclear membrane to isolate it from the rest of the cell. Prokaryotes also do not have membrane-bound organelles as do eukaryotes. They use free ribosomes to synthesize proteins. Prokaryotes also have a plasma membrane surrounding the entire cell, and most prokaryotes have a cell wall. The Kingdom Monera is the only place where prokaryotes are found. This means that all archaebacteria and eubacteria are prokaryotes. A handful of dirt has more prokaryotes in it than the amount of people who have ever walked the earth.

Prokaryotes are the single-celled organisms, such as bacteria, and are roughly one micrometer in diameter. Unlike Eukoryotes, prokaryotes do not have a nucleus that houses its genetic material. Rather, the genetic material of a prokaryote cell consists of a large DNA molecule compacted in an area of cytoplasm called the nucleiod region. The nucleoid region is protected and encased by the cell wall, or cell membrane, the outer layering of the cell (similar to human's skin). Finally, a flagellum (flagetta - plural), a rudder-like device, affords the prokaryote the luxury of mobility.

One differentiating characteristic is that prokaryotes are asexual, meaning their offspring nearly always bear the exact characterisitcs of the parent cell. (In fact, the cell essentially replicates itself according to its own DNA and then divides itself from the newly created cell.) Since the Prokaryotes exhibit this asexual behavior as opposed to sexual behavior, where a recombination of chromosones occur to form unique entities (as with humans), evolution of the prokaryotic cell has been fairly stagnant over its two billion year lifespan. Additionally, at the time of Symbiosis, prokaryotes were anaerobic, that is, they did not respirate oxygen as a fundamental necessity to live. As far as nutrition distribution, the small size of prokaryotes provides a high ratio of surface area to volume, making diffusion an adequate means for distributing nutrients throughout the cell.

Abundance. Prokaryotic cells and fossils have have been found in almost every conceivable environment on the earth, from hot sulfur springs to beneath the ocean floor and within larger cells. Overall, Prokaryotes account for a significant portion of the past and present biomass on earth.

Prokaryotes are single-celled organisms distinguished from single- and multi-celled eukaryotes by a number of features. The name refers to the absence of a membrane bound structure (nucleus) enclosing the genetic material. The name is derived from the Greek words pro, meaning before (in time or position), and karuon, meaning nut or kernal (referring to the nucleus). Prokaryotes have a single circular chromosome, sometimes called a genophore to distinguish it from structurally dissimilar eukaryotic chromosomes. In most the genophore is located in a nucleoid region, distinguished in electron micrographs by less intense staining than the surrounding cytoplasm. Prokaryotes also lack endoplasmic reticulum and organelles characteristic of most eukaryotes. Most prokaryote cells are smaller than eukaryotes, on the order of 1 - 5 micrometers, compared to 10 - 100 micrometers. As always in the realm of life however, there are exceptions. One type of rod-shaped prokaryote found in marine environments is about half of millimeter (500 micrometers) in length! Although prokaeryotes are thought of as single-celled organisms, some live in transient aggregations, and some form true colonies. In some of the colonial forms there is even functional specialization among two or more different cells, a kind of simple multicellular organization.

In the three domain system the term prokaryote is used to describe the chief morphological characteristic of organisms in the domains Archaea and Bacteria, and is not applied to any taxonomic category. In the system of Margulis and Schwartz Archaea and Bacteria are subkingdoms in the superkingdom Prokarya.

Many people are only familiar with prokaryotes, bacteria, as disease causing organisms. Many kinds of bacteria are pathogens of humans and other eukaryotes, but the vast majority are not. Prokaryotes are also ecologically important as photosynthetic or chemosynthetic producers, as decomposers, and as participants in the global cycling of nutrients such as carbon, nitrogen, and sulfur. Indeed, without decomposition by prokaryotes, releasing nutrients for uptake by other organisms, or without the chemical conversions of carbon and nitrogen compounds, other organisms could not exist.

The names of the two major classes of cells—eukaryotes and prokaryotes—betray certain scientific assumptions about how the two are organized. Eukaryotes include all of the cells of plants and animals and are distinguished from the prokaryotic cells of bacteria by their structural complexity. Specifically, eukaryotic cells contain membrane-bounded compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, the membrane-delimited compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote—literally, true nucleus—its name. In contrast the prokaryote cell contains no membrane-delimited compartments and thus its name reflects its status as the proto-eukaryote. Most dangerous about these names is that they allow scientists to make assumptions about the way metabolism is carried out inside each cell type. In stark contrast to the eukaryote, the prokaryote has long been thought of as just a bag of enzymes in which reactions take place almost by random encounters.

Prokaryote: A unicellular organism lacking a nuclear membrane, a discrete nucleus, and other specialized compartments within the cell. Bacteria and viruses are prokaryotes.

It appears that life arose on earth about 4 billion years ago. The simplest of cells, and the first types of cells to evolve, were prokaryotic cells. Bacteria are the best known and most studied form of prokaryotic organisms, although the recent discovery of a second group of prokaryotes, called archaea, has provided evidence of a third cellular domain of life and new insights into the origin of life itself.

Prokaryotes are unicellular organisms that do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime secreted by the cells. k, j. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of our bodies.

Prokaryotes are distinguished from eukaryote on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack any of the intracellular organelles and structures that are characteristic of eukaryotic cells. Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili--proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosome and various sorts of inclusions.

Prokaryotes are mostly unicellular organisms without a nucleus, in contrast to eukaryotes, organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between prokaryote and eukaryote cell structure is the most important in the living world. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. However, Woese has proposed dividing them into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) on the supposition that these have separate origins. This controversial arrangement is called the three-domain system. The name prokaryote comes from the Greek pros meaning before and karyon meaning nut, referring to the nucleus. Prokaryotes also lack cytoskeletons and membrane-bound cell compartments such as vacuoles, endoplasmic reticulum, mitochondria and chloroplasts. In eukaryotes, the latter perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur within the cell membrane, and endosymbionts are extremely rare. They are usually much smaller than eukaryotic cells.

Prokaryotes have a single chromosome, contained within a nucleoid region rather than a membrane-bound nucleus, but may also have various small circular pieces of DNA called plasmids spread throughout the cell. Reproduction is exclusively asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.

It is generally accepted that the first living cells were some form of prokaryote, and they are known as fossils from over 3.5 billion years ago. Some have suggested structures within a Martian meteorite should be interpreted as fossil prokaryotes, but this is extremely doubtful.

Archaebacteria and Eubacteria also known as the "prokaryotes" and are usually referred to as bacteria are structurally the simplest kinds of organism. They resemble the earliest forms of life. Most are unicellular with cell membrane and a rigid cell wall. There are no mitochondria, chloroplasts, nuclei, or other membrane bound organelles within the cell. The DNA exists as one large, circular molecule suspended in the cytoplasm. The DNA is not associated with histone proteins and does not form into chromosomes. Reproduction in bacteria is by fission (cell division). Most bacteria are heterotrophic so they need to gain nutrients from the environment. Many are saprophytic, meaning they send out digestive enzymes into the environment and thereafter take up the digested nutrient molecules. Some bacteria are parasitic and can only survive on other living organisms. Some are pathogens that cause diseases such as strep throat or gangrene. Other bacteria are autotrophic, meaning they can produce their own food. Autotrophic bacteria can be either photosynthetic utilizing energy from the sun or chemosynthetic utilizing energy from non-organic chemical reactions. Eubacteria are the most numerous organisms on earth and they flourish in almost every environment. Billions of them can be found in a handful of soil. d, d, k. They are also found in your digestive tract, on your skin, and between your teeth. Archaebacteria are found in extreme environments such as hydrothermal vents on the ocean floor which reach temperatures well in excess of 100°C, and within cracks of rocks in the Antarctic desert - the driest and coldest place on earth. Archaebacteria are also fount in such extremes as salty water, anaerobic water, or water rich in sulfur.

The timescale of prokaryote evolution has been difficult to reconstruct because of a limited fossil record and complexities associated with molecular clocks and deep divergences. However, the relatively large number of genome sequences currently available has provided a better opportunity to control for potential biases such as horizontal gene transfer and rate differences among lineages. We assembled a data set of sequences from 32 proteins (~7600 amino acids) common to 72 species and estimated phylogenetic relationships and divergence times with a local clock method.

Kingdom Monera: The Prokaryotes.

The Monerans are the most numerous and widespread organisms on earth. They comprise the only kingdom of prokaryotic organisms, those which lack a nucleus or other membrane-bounded organelles. External to the plasma membrane, most bacteria have a cell wall partially composed of peptidoglycan, a complex structural molecule not found in eukaryotic cells. Let's have a look at the basic flavors of bacteria.

ARCHAEBACTERIA There are three types of archaebacteria, the most ancient of all living things. The thermoacidophiles live in the extremely hot, acidic water and moist areas within and surrounding sulfur hot springs. So closely adapted are they to their bubbly environment that they die of cold at temperatures of 55oC (131oF)! Methanogens are obligate anaerobes (free oxygen kills them) which oxidize CO2 during cellular respiration to produce methane (CH4) as a waste product. l, b, h, k, a. Although RNA sequencing suggests that all ten known species are evolutionarily related, they exist in environments as diverse as scalding volcanic deep-sea vents and the intestines of mammals. The reason you can light a puff of flatulence (should you choose to go into show business) is because of the symbiotic methanogens inside your guts.

Strict halophiles live in extremely salty solutions such as the Dead Sea, the Great Salt Lake and that can of pickled herring you left open in the cupboard. Their pink carotenoid pigments make them conspicuous when the bacteria are present in large concentrations, as they are on the shores of some salty, land-locked lakes.

EUBACTERIA The "true bacteria" are classified on the basis of several characteristics, of which perhaps the most familiar is the Gram Stain method.

Gram negative Eubacteria About 75% of known eubacteria are gram negative. They include the gliding bacteria, the spirochetes, the curved (vibrios) and spiral (spirillae) bacteria, gram-negative rods, gram-negative cocci, rickettsias, chlamydias and the photosynthetic cyanobacteria. Gram negative bacteria form an extremely diverse group. The fact that they are all gram-negative does not necessarily imply that they comprise a monophyletic taxon.

Gram positive Eubacteria Not as diverse as the gram-negative bacteria, the gram-positives still make up an impressively varied group. This division includes the gram-positive rods, gram-positive cocci, and the actinomycetes, which exhibit superficial similarity and function (but no evolutionary relationship) to the (eukaryotic) fungi. 

MYCOPLASMAS These are the smallest living cells ever discovered, and are believed to have the minimum amount of DNA needed to code for a functioning cell. They lack the cell wall characteristic of the other three types of bacteria. Most mycoplasmas exist as intracellular plant or animal parasites, a life history which protects them from environmental osmotic stresses as long as the host cell is functioning properly. Penicillin, an antibiotic lethal to most other bacteria because it interferes will cell wall formation, is not effective against the naked little mycoplasmas.

Archaea - these organisms are microscopic prokaryotes. When the first ones were discovered (in 1977), they were considered bacteria. However, when their ribosomal RNA was sequenced, it became obvious that they bore no close relationship to the bacteria and were, in fact, more closely related to the eukaryotes (including ourselves!) For a time they were referred to as archaebacteria, but now to emphasize their distinctness, we call them Archaea

Bacteria and archaea belonging to deep-branching lineages in rDNA-based phylogenies frequently share common phenotypic and metabolic properties. These in turn suggest inferences about their ancestral geochemical environments. Although there is considerable metabolic diversity among the energy metabolisms of early diverging bacteria and archaea (sulfur reduction, methanogenesis, fermentation of organic carbon compounds, hydrogen oxidation), anaerobiosis and thermophily emerge as common themes, possibly connected to complex CO2/H2 autotrophy. A systematic molecular survey of prokaryotic biodiversity within anaerobic and/or hot marine environments, such as gradient habitats of hydrothermal vent sites, stratified marine water columns and anaerobic sediments, will show in greater detail the connection between microbial metabolisms and habitats, and the limits of prokaryotic tolerance towards extreme environments.

By examining the evolution of microorganisms in these habitats, we will also gain a better understanding of how their evolution was connected to the evolution of an oxygen-rich atmosphere.

The combined results of these biodiversity surveys with molecular and cultivation approaches will delineate habitat range and environmental tolerance limits of prokaryotic and eukaryotic populations in situ.

Cyanobacteria are Prokaryotes, which are known to be the earliest forms of life, throughout time they have adapted to the changing earth, and in turn help it evolve. Prokaryotes belong to the kingdom Monera (Greek for single) and are small celled organisms that lack membrane-enclosed organelles. They have cell walls, but their composition differs from those of plants, protisits and fungi. They are similar to Eukaryotes, but they have smaller and simpler genomes, and differ in genetic replication, protein synthesis, and recombination. Prokaryotes are photosynthetic and aquatic and can exist in almost any environment, and individually their impact may be microscopic, but collectively their impact on the earth is immense. Prokaryotes are divided based on the differences on how they receive their nutrition (how they obtain energy and carbon). Cyanobacteria belong to the category termed photoautorophs, which use light to drive the synthesis of organic compounds from carbon dioxide.

The prokaryotes include the bacteria and the bluegreen bacteria (or "algae") and the prochlorons. There are several different groups of bacteria and they are probably no closer related to each other than they are to the Cyanobacteria but we will consider them together for convenience.

PROKARYOTE CHARACTERISTICS

Prokaryotic cells differ from Eukaryotic cells in several important respects, many of which have already been considered.

1. Size. They are usually much smaller then eukaryotes. 1-5m m rather than 10-100 of eukaryotes. Most are about 1m m.

2. They have no envelope-surrounded nucleus.

3. Their DNA has much less protein associated with it and what is present is easily dislocated. Consequently prokaryotes were long thought to have no protein associated with the DNA.

4. The DNA is a continuous loop, or circle. Smaller circles, or plasmids, may be present.

5. There is no mitosis or meiosis but there is, of course, chromosome replication. Division is by binary fission.

6. There are no independent internal membranes and consequently no membrane surrounded organelles. Thus there are no chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, Golgi.

7. The enzymes, pigments, and electron carriers usually associated with membranes are located on invaginations of the plasma membrane known as mesosomes.

8. The cell wall is unique. It is not cellulose rather another polymer of glucose-like monomers. The polymer is known as a peptidoglycan. These are polymers of substituted glucose crosslinked by short polypeptides. They are known as N-acetylglucosamine and N-acetylmuramic acid. In gram negative bacteria there is also an outer layer of polysaccharide. Protects from lysis in hypoosmotic environment.

9. The cell membrane and cytoplasm are similar to those of eukaryotes except that there is no cytoskeleton in the cytoplasm and no steroids in the membrane.

10. The ribosomes are smaller.

11. There is much less DNA. There is about 1mm of DNA in an E. coli cell whereas one of your cells has about 2m.

12. The flagellum, if present, is radically different from that of eukaryotes. There is no tubulin/dynein system. The flagellum is made of flagellin, and is naked protein outside the membrane.

There are more then 10,000 species of bacteria and their classification is based largely on clinical and laboratory convenience rather than phylogeny. Recent molecular systematic studies have shed some light on the relationships within the Monera.

There apparently was a very early split of the monerans into the Archaebacteria and the Eubacteria. Most modern bacteria are Eubacteria and the Archaebacteria persist as a small number of species largely restricted to extreme environments such as hot springs, high salinities, high acidities, anaerobic environments, etc. e, g, a, d, f. Archaebacteria have no peptidoglycan in the cell wall and have unique phospholipids in the membrane. Ribosomal proteins resemble those of eukaryotes and the archaebacteria may be more closely related to Eukaryotes than are the eubacteria.

The Eubacteria include the gram positive bacteria as well as many groups of gram negative bacteria, the photosynthetic bacteria as well as the Cyanobacteria and spirochaetes.

Any of a group of relatively simple one-celled living things lacking a nucleus and other features found in the more complex cells of all other living things, called eukaryotes. The two major types of prokaryotes are bacteria and cyanobacteria.

The prokaryotes known as archaebacteria are primitive anaerobes (living things that do not require oxygen ) inhabiting extreme environments of high temperature, high salt, or high acidity. All other bacteria are called eubacteria and are classified according to their shape: for example, bacilli are rod-shaped. Eubacteria live in both aerobic (with oxygen) and anaerobic (without oxygen) environments.

Some prokaryotes move by rotating long whip-like structures called flagella. Some species also have slender hair-like extensions called pili, used for attachment. The cell membrane of prokaryotes, similar in structure to that of eukaryotes, is different in composition. Eukaryotes contain organelles, including chloroplasts and mitochondria, that are absent in prokaryotes. Prokaryotes have a single molecule of deoxyribonucleic acid (DNA). This DNA molecule is not enclosed in a nucleus, is not associated with protein, and is not double-stranded, as it is in eukaryotes.

Prokaryotes are cellular organisms lacking a true nucleus and nuclear membrane. Their nuclear material consists of a single double-stranded DNA molecule, not associated with basic proteins. The microorganisms, comprising the bacteria and blue-green bacteria (formerly blue-green algae), are predominantly unicellular but may have filamentous, mycelial, or colonial forms. All (except the Mollicutes and Archaeobacteria) have a true cell wall containing peptidoglycan, and all reproduce by cell fission.

Prokaryotes are the original inhabitants of this planet, the first successful today's would have looked very like some of today's Archaea. Both Archaea and Bacteria evolved somewhere between 3 or 4 billion years ago as far as we are able to tell from the fossil record. This means they have been around twice as long as the Protozoans and more than 3 times as long as animals.

Prokaryotes are the toughest of the tough when it come to living things. They hold all the records for living in the coldest, hottest, most acidic and most highly pressurized environments. They live in incredible places such as miles beneath the earth in bare rock, under glaciers, floating around in clouds and miles down on the sea floor at temperatures greater than 100 C. They are also the worlds experts at surviving bad times. In 2000AD scientists at West Chester University Pennsylvania succeeded in waking up the resting spores of a bacterium (Bacillus permians) that was last active 250 million years ago. The question this caused scientists to ask was. "Is it possible some Bacteria may be immortal ??"

Prokaryotes make up most of what is studies by microbiologists, the rest being some single celled fungi and algae. Microbiology is a very important field of research these days. Contributing greatly to our studies of medicine, bioengineering, genetics and evolution.

Prokaryotes are single celled organisms that do not have a nucleus, mitochondria or any other membrane bound organelles. In other words neither their DNA nor any other of their sites of metabolic activity are collected together in a discrete membrane enclosed area. Instead everything is openly accessible within the cell some free floating some bound to the walls of the cell membrane, it is this which separates them from the Eukaryotes. Some bacteria have internal membranes, invaginations of the cell membrane as sites of metabolic activity, these membranes do not enclose a separate area of the cytoplasm. For more on Prokaryote vs. Eukaryote cells see Cells.html

Prokaryotes come in two sorts, Archaea and Bacteria. Both of these are a Kingdoms of life in their own rite. this is because they are as different, if not more different, from each other, as they are from protozoans, fungi, plants and us. At the bottom of this page is a table listing most of the major differences between Archaea, Bacteria and Eukaryotes.

A prokaryotic cell is a cell which doesn't have a nucleus, while eukaryotic cells have nuclei. There are some differences between prokaryotic cells and eukaryotic cells which are relevant to gene recognition. In prokaryotic cells most of the DNA sequence is coding for protein. For example, almost 70% of the genome of the bacterium H.influenzea is coding. Also, each gene is one continuous stretch of bases. That is, there are no introns in the coding region.

Bacteria may be conveniently divided into two further groups, depending upon their ability to retain a crystal violet-iodine dye complex when cells are treated with acetone or alcohol. This reaction is referred to as the Gram reaction: named after Christian Gram, who developed the staining protocol in 1884. It may seem a very arbitrary basis on which to build one's classification system. This reaction, however, reveals fundamental differences in the structure of bacteria. Electron microscopy shows that Gram-negative and Gram-positive bacteria have fundamentally different structures, related to the composition of the cell wall, amongst other things. Cells with many layers of peptidoglycan can retain a crystal violet-iodine complex when treated with acetone. l, k, h, l, a. These are called Gram-positive bacteria and appear blue-black or purple when stained using Gram's method. Gram-negative bacteria have only one or two layers of peptidoglycan and cannot retain the crystal violet-iodine complex. These need counterstaining with another dye to be seen using Gram's method. A red dye such as dilute carbol fuchsin is often used.

The cell wall of Gram-positive bacteria lies beyond the cell membrane and is largely made up of pepidoglycan. There may be up to 40 layers of this polymer, conferring enormous mechanical strength on the cell wall. Other polymers including teichoic and teichuronic acids also lie in the cell walls of Gram-positive bacteria. These act as surface antigens.

In contrast to Gram-positive cells, the cell envelope of Gram-negative bacteria is complex. Above the cell membrane is a periplasm. This area is full of proteins including enzymes. One or two layers of peptidoglycan lie beyond the periplasm. Gram-negative bacteria are thus mechanically much weaker than Gram-positive cells. Beyond the peptidoglycan of the Gram-negative cell wall lies an outer membrane. This has protein channels - porins - through which some molecules may pass easily. The outer side of the Gram-negative outer membrane contains lipopolysaccharide. This provides the antigenic structure of the surface of Gram-negative bacteria and also acts as endotoxin. It is this that is responsible for eliciting the symptoms of Gram-negative shock if it gains access to the bloodstream. Porins and Outer Membrane Proteins (OMPs) act as transporters through the outer membrane.

The bacterial chromosomal DNA is located in a region of the cell known as the nucleoid. Bacteria, being prokaryotes, do not have a true, membrane-bound nucleus. Bacteria carry a single chromosome that is circular in structure.

Additional genetic information may be carried on plasmids. These are circles of DNA that lie within the bacterial cytoplasm and replicate independently of the chromosome. Plasmids carry genes that are typically not essential for survival, but that can confer selective advantages in special circumstances. Not all bacterial cells carry plasmids, but some can carry several plasmids in a single cell. R-factors are plasmids that carry genes that confer antibiotic resistance on the cell. Toxins are sometimes coded for by plasmid genes.

Lysogens are bacteria that have been stably infected with a bacteriophage and that carry the virus as a 'prophage'. The bacteriophage DNA is integrated into the genome of the bacterium. Under special conditions, lysogens can burst to release new bacteriophage particles. Lysogens can be very important. The gene for diphtheria toxin is carried by a prophage, and only the lysogenic strains of Corynebacterium diphtheriae can cause diphtheria.

The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotes have a nucleus and membrane-bound organelles, while prokaryotes do not. The DNA of prokaryotes floats freely around the cell; the DNA of eukaryotes is held within its nucleus.

Prokaryotes have a cell wall composed of peptidoglycan, a single large polymer of amino acids and sugars. Many types of eukaryotic cells (e.g. Plants) also have cell walls, but none made of peptidoglycan. many Bacteria have external structures called Pili that they use to attach to other cells.

Some similarities between the two types of cells (prokaryotic and eukaryotic) are: They both have DNA as their genetic material. They both have Plasma membranes. They both have ribosomes to make proteins.

Classifying bacteria on the basis of their morphology is extremely difficult; bacteria are generally quite small and have simple shapes. In addition to shape, bacteria have traditionally been identified and classified on the basis of their biochemistry and the conditions under which they grow.

A bacterium (plural: bacteria) is an organism belonging to the domain bacteria, in the three domain scheme. Traditionally classified as one of the five kingdoms, bacteria are microscopic, mostly single celled and their cell structure is relatively simple. Since they lack the nucleus and organelles of the more complex cells called "eukaryotes", bacteria are considered to be "prokaryotes."

Acetic acid bacteria are bacteria that derive their energy from the oxidation of ethanol to acetic acid during respiration. They are Gram-negative rod-shaped bacteria that require oxygen.

The acetic acid bacteria are found in nature where ethanol is being formed as a result of yeast fermentation of sugars and plant carbohydrates. They can be isolated from the nectar of flowers and from damaged fruit. Other good sources are fresh apple cider and unpasteurized beer which has not been filter sterilized. In these liquids the acetic acid bacteria grow as a surface film due to their aerobic nature and active motility. Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine.

Some genera, such as Acetobacter, can eventually oxidize acetic acid to carbon dioxide and water using Krebs cycle enzymes. Other genera, such as Gluconobacter, doesn't further oxidize acetic acid, as it does not have a full set of Krebs cycle enzymes.

As these bacteria produce acid, they are unusually acid tolerant, growing well below pH 5.0, although the pH optimum for growth is 5.4-6.3.

Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert alcohol (ethanol) to acetic acid in the presence of air. There are several species within this genus, and there are other bacteria capable of forming acetic acid under various conditions; but all of the Acetobacer are known by this characteristic ability.

Acetobacter are of particular importance commercially, because:

they are used in the production of vinegar (intentionally converting the ethanol in the wine to acetic acid) they can destroy wine which it infects by producing excessive amounts of acetic acid or ethyl acetate, both of which can render the wine unpalatable. The growth of Acetobacter in wine can be suppressed through effective sanitation, by complete exclusion of air from wine in storage, and by the use of moderate amounts of sulfur dioxide in the wine as a preservative.

Acetobacter can be easily distinguished in the laboratory by their growth of colonies on a medium containing about 7% ethanol, and enough calcium carbonate to render the medium partially opaque. When Acetobacter colonies form enough acetic acid from the ethanol, the calcium carbonate around the colonies dissolves, forming a very distinct clear zone. b, e, l, d, j. Bordetella is a genus of proteobacteria. Members of the species B. pertussis and occasionally B. parapertussis cause pertussis or whooping cough in humans. Several other species cause similar disease in other mammals, such as B. bronchiseptica, and in birds, such as B. avium and B. hinzii.

Campylobacter jejuni is a species of curved, rod-shaped bacterium commonly found in animal faeces. It is one of the most common causes of human diarrhoea in developed countries. Food poisoning caused by Campylobacter species can be severely debilitating but is rarely life-threatening. It has been linked with subsequent development of the neurodegenerative disease Guillain-Barré syndrome (GBS).

It is commonly associated with chickens and has been found in wombat and kangaroo faeces, being a cause of bushwalkers' diarrhoea. It naturally colonises many different bird species.

In the laboratory, Campylobacter is grown on specially selective agar plates at 42°C, the normal avian body temperature, rather than 37°C, the temperature at which other bacteria are often grown. Since the colonies are oxidase positive, they will usually only grow in scanty amounts on the plates. Microaerophilic conditions are required for luxurious growth.

Normally no antibiotics are given, because the disease is self-limiting. However, severe or prolonged cases may require ciprofloxacin, erythromycin or norfloxacin.

Bacteria that are Gram-negative are not stained dark blue or violet by Gram staining, in contrast to Gram-positive bacteria.

The difference lies in the cell wall of the two types; Gram-positive bacteria have a high amount of peptidoglycan in their cell wall which the stain interacts with, while Gram-negative bacteria have a cell wall made primarily of lipopolysaccharide. The Gram-negative cell wall is similar to a cytoplasmic membrane, typically only a few layers thick and generally much thinner than Gram-positive types.

Many species of Gram-negative bacteria are pathogenic. This pathogenic capability is usually associated with certain components of their cell walls, particularly the lipopolysaccharide (endotoxin) layer.

The proteobacteria are a major group of Gram-negative bacteria, including for instance Escherichia coli, Salmonella, and other Enterobacteriaceae, Pseudomonas, Moraxella, Helicobacter, Stenotrophomonas, Bdellovibrio, acetic acid bacteria, Legionella and a great many others. Other notable groups of Gram-negative bacteria include the cyanobacteria, spirochaetes, green sulfur and green non-sulfur bacteria.

Caulobacter crescentus is a gram-negative, oligotrophic bacterium widely distributed in aquatic environments. It plays an importante role in the carbon cycle.

It is an important model to cellular differentiation and one of its most perceptible characteristics is that its two child-cells are very different from each other, one being mobile and the other fixed. The mobile one has a flagellum and swims until it finds a favorable environment, at which point it loses its flagellum and develops a new structure that lets the cell fix itself to a substrate.

The optimal temperature to the growth of Caulobacter is around 30°C and its generational period is 2.5 hours.

The Enterobacteriaceae are a large family of bacteria, including many of the more familiar pathogens, such as Salmonella and Escherichia coli. Genetic studies place them among the Proteobacteria, and they are given their own order (Enterobacteriales), though this is sometimes taken to include some related environmental samples.

Members of the Enterobacteriaceae are rod-shaped, and are typically 1-5 μm in length. They are facultative anaerobes, producing energy through fermentation of sugars, producing lactic acid and various other end products. They also reduce nitrate to nitrite. Like all proteobacteria, they have Gram-negative stains, and can be distinguished from similar bacteria by the absence of oxidase. Most have many flagella used to move about, but a few genera are non-motile.

Many members are a normal part of the flora found in the intestines of humans and other animals, while others are found in water or soil, or are parasites on a variety of different animals and plants. Escherichia coli, better known as E. coli, is one of the most important model organisms and its genetics and biochemistry have been closely studied.

Escherichia coli (usually abbreviated to E. coli) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of food. Its presence in groundwater is a common indicator of fecal contamination. ("Enteric" is the adjective that describes organisms that live in the intestines. "Fecal" is the adjective for organisms that live in feces, so it is often a synonym for "enteric.") The name comes from its discoverer, Theodor Escherich. It belongs among the Enterobacteriaceae, and is commonly used as a model organism for bacteria in general.

The number of individual E. coli bacteria in the feces that one human passes in one day averages 1011 (= one with eleven zeroes after it) to 1013. All the different kinds of fecal coli bacteria and all the very similar bacteria that live in the ground (in soil or decaying plants, of which the most common is Enterobacter aerogenes) are grouped together under the name "coliform" (meaning "like coli") bacteria. Technically, the "coliform group" is defined to be all the aerobic and facultative anaerobic, non-spore-forming, Gram-negative, rod-shaped bacteria that ferment lactose with the production of gas within 48 hours at 35°C (in the body, this gas is released as flatulence).

In the fields of water purification and sewage treatment, E. coli was chosen very early in the development of the technology as an "indicator" of the pollution level of water, meaning the amount of human fecal matter in it. The main reasons for using E. coli are that there are a lot more coliforms in human feces than there are pathogens (such as Salmonella typhosa, which causes typhoid), and E. coli is usually harmless, so it can't "get loose" in the lab and hurt anyone. It can be misleading to use E. coli as an indicator of human fecal contamination because there are other environments in which E. coli grows well, such as paper mills.

There are, however, three situations where the otherwise harmless E. coli can cause illness:

When the bacteria get out of the intestinal tract and into the urinary tract, they can cause an infection sometimes referred to as "honeymoon cystitis" because intercourse can lead to introduction of bacteria into the bladder. However urinary tract infection is seen in both males and females and in roughly equal proportions if you take all ages. Since bacteria invariably enter the urinary tract through the urethra poor toilet hygiene can predispose to infection but other factors are also important (pregnancy in women, prostate enlargement in men) and in many cases the initiating event is unclear. When the bacteria get out of the intestinal tract through a perforation (= a hole or tear, which could be caused by an ulcer, for example) and into the abdomen, they usually cause an infection called "peritonitis" that can be fatal, although E. coli are extremely sensitive to antibiotics such as streptomycin, treatment with antibiotics is usually effective. Certain strains of E.coli are toxigenic (some produce a toxin very similar to that seen in dysentery) and can cause food-poisoning usually associated with eating contaminated meat (contaminated during or shortly after slaughter or during storage or display). Severity of the illness varies considerably; it can, rarely, be fatal, but is more often mild. d, g, a, e, h. A "strain" of E. coli is a family with some particular characteristics that make it recognizable from other E. coli strains, the way poodles are recognizable from other strains (or "breeds") of dogs, and different strains of E. coli live in different kinds of animals, so it is possible to tell whether fecal material in water came from humans or from birds, for example. New strains of E. coli arise all the time from the natural biological process of mutation, and some of those strains have characteristics that can be harmful to a host animal. Although in most healthy adult humans such a strain would probably cause no more than a bout of diarrhea, and might produce no symptom at all, in young children, or in people who are or have recently been sick, or in people taking certain medications, an unfamiliar strain can cause serious illness and even death. A particularly virulent example of such a strain of E. coli is E.coli O157:H7.

Because of its ubiquity, E. coli is frequently studied in cellular biology. Its structure is clear, and it makes for an excellent target for novice and intermediate students of the life sciences.

Klebsiella pneumoniae is a gram-negative rod-shaped bacteria, and clinically the most important member of the Klebsiella genus of Enterobacteriaceae. It can cause pneumonia although it more commonly implicated in hospital-acquired urinary tract and wound infections, particularly in people with weakened immune systems. It is an increasing problem on hospitals because of the evolution of antibiotic resistant strains.

The Danish scientist Hans Christian Gram (1853-1928), developed the technique now known as Gram staining in 1884 to discriminate between K. pneumoniae and pneumococci.

Plesiomonas shigelloides is a Gram-negative, rod-shaped bacterium which has been isolated from freshwater, freshwater fish, and shellfish and from many types of animals including cattle, goats, swine, cats, dogs, monkeys, vultures, snakes, and toads. It has been associated with causing human disease, but this has not yet been proven. It is placed among the Enterobacteriaceae.

Proteus vulgaris is a rod-shaped Gram negative bacterium (a chemoheterotroph) that inhabits the intestinal tracts of animals and can be pathogenic. Proteus vulgaris is in the proteobacteria.

In humans, it can cause urinary tract infections and wound infections.

Serratia marcescens is a Gram negative bacterium, a human pathogen of the family Enterobacteriaceae. It is involved in nosocomial infections, particularly urinary tract infections and wound infections.

Most strains are resistant to several antibiotics because of the presence of R-factors on plasmids.

In the 1950s it was erroneously believed to be non-pathogenic and its reddish coloration was used in school experiments to track infections.

Because of its red pigmentation, and its ability to grow on bread, it has been evoked as a naturalistic explanation of Medieval accounts of the "miraculous" appearance of blood on the eucharist.

Shigella are Gram-negative, nonmotile, nonsporeforming rod-shaped bacteria. They are pathogens of humans and other primates, causing shigellosis. Depending on age and condition of the host, as few as 10 cells depending on age and condition of host can be enough to cause an infection. The disease is caused when virulent Shigella organisms attach to, and penetrate, epithelial cells of the intestinal mucosa. After invasion, they multiply intracellularly, and spread to contiguous epitheleal cells resulting in tissue destruction. Some strains produce enterotoxin and Shiga toxin (very much like the verotoxin of E. coli O157:H7).

Yersinia pestis is a species of rod-shaped bacterium, belonging to the family Enterobacteriaceae. It is the infectious agent of bubonic plague, and can also cause pneumonic plague and septicemic plague.

It was discovered by Alexandre Yersin in 1894, who was a student of the "Pasteur school". Shibasaburo Kitasato was another biologist, from the "Koch school" engaged in finding the causative agent of plague. However, it was Yersin who actually linked plague with Yersinia pestis. This coccobacillus was originally called Pasteurella pestis, and was renamed after Yersin.

Francisella tularensis is a pathogenic bacterium, which causes the disease tularemia or rabbit fever. It is an intracellular parasite, primarily spread through insect vectors.

Haemophilus influenzae, also called Pfeiffer's bacillus, is a non-motile Gram-negative coccobacillus first described in 1892 by Dr. Robert Pfeiffer during the influenza pandemic. It is generally aerobic, but can grow as a facultative anaerobe. b, b, d, i, e. Haemophilus influenzae was mistakenly considered to be the cause of the common flu until 1933, when the viral etiology of the flu became apparent. Still, Haemophilus influenzae is responsible for a wide range of clinical diseases. Because of its small genome, Haemophilus influenzae became the first free-living organism with its entire genome sequenced.

Serotypes In 1930, 2 major categories of H influenzae were defined: the unencapsulated strains and the encapsulated strains. The pathogenesis of H. influenzae infections is not completely understood, although the presence of the encapsulated type b (HiB) is known to be the major factor in virulence. Their capsule allows them to resist phagocytosis and complement-mediated lysis in the non-immune host. Unencapsulated strains are less invasive, but they are able to induce an inflammatory response that causes disease. Vaccination with Hib conjugate vaccines is effective in preventing infection, and several vaccines are now available for routine use.

Diseases Naturally-acquired disease caused by H. influenzae seems to occur in humans only. In infants and young children, HiB causes bacteremia and acute bacterial meningitis. Occasionally, it causes obstructive laryngitis, cellulitis, osteomyelitis and joint infections. Unencapsulated H. influenzae causes ear infections and sinusitis in children and is associated with pneumonia.

Helicobacter pylori is a bacterium that infects the mucus lining of the human stomach. Many peptic ulcers and some types of gastritis are caused by H. pylori infection, although most humans are infected and will never develop symptoms. The bacterium is helix shaped (hence the name helicobacter) and can literally screw itself into the stomach lining to colonize it.

The bacterium was first described in 1982 by two Australian scientists Robin Warren and Barry Marshall, who isolated and cultured organisms from human mucosal specimens. The bacterium was initially called Campylobacter pyloridis, then C. pylori (after a correction to the Latin grammar) and finally, after DNA sequencing showed that the bacterium didn't belong in the campylobacter genus, it was placed in its own genus Helicobacter. The name pylori comes from the Latin word pylorus (meaning gatekeeper), and refers to the circular opening leading from the stomach into the duodenum. In their 1982 paper, Warren and Marshall contended that most stomach ulcers and gastritis were caused by colonization with this bacterium, not by stress or spicy food as the medical community had long assumed.

The medical community was slow to recognize the role of this bacterium in stomach ulcers and gastritis, believing that no bacterium could survive for long in the acidic environment of the stomach. Finally, after further studies were done, including one study in which Marshall drank a test tube of H. pylori, developed gastritis, and treated himself with antibiotics (thereby satsifying three out of the four Koch's postulates for disease) the medical community began to come around. In 1994, the National Institutes of Health published an opinion stating that most recurrent gastric ulcers were caused by H. pylori, and recommended that antibiotics be included in the treatment regimen.

Today, many stomach ulcers are treated with antibiotics effective against H. pylori. Some other species of the helicobacter genus have now been identified in other mammals and some birds.

Structure of the bacterium H. pylori is a spiral-shaped gram-negative bacteria, about 3 micrometers long with a diameter of about 0.5 micrometers. It has 4-6 flagella. It is microaerophilic, i.e. it requires oxygen but at lower levels than those contained in the atmosphere.

Model of H. Pylori ureaseWith its flagella and its spiral shape, the bacterium drills through the mucus layer of the stomach and attaches to epithelial cells. It contains the enzyme urease which converts urea into ammonia and bicarbonate. The ammonia is useful to the bacterium since it partially neutralizes the very acidic environment of the stomach (whose very purpose is to kill bacteria). Ammonia is however toxic to the epithelial cells. A molecular model of the H. pylori urease enzyme is shown in the figure to the right.

Infection and diagnosis About 2/3 of the world population is infected by the bacterium. Under poor sanitary conditions, one commonly finds infected children; in the U.S., older people (about 50% of those over the age of 60, 20% of those under the age of 40), and poor people are more likely to be infected. The infection apparently persists for life; the immune system cannot fend off the organism. The bacteria have been isolated from feces, saliva and dental plaque of infected patients, which suggests possible transmission routes. One can test for H. pylori infection with blood antibody tests, breath tests (where the patient drinks 14C or 13C labeled urea, which the bacterium metabolizes to carbon dioxide that can be detected in the breath), or endoscopy.

Eradication therapy In gastric ulcer patients where H. pylori is present, the first-line therapy is the eradication of the organism causing the ulcer. The standard first-line therapy is a one week triple-therapy of amoxicillin, clarithromycin and omeprazole - though sometimes a different proton pump inhibitor is substituted, or metronidazole is used in place of amoxicillin in those allergic to penicillin. Such a therapy has revolutionised the treatment of gastric ulcers and has made a cure to the disease possible, where previously symptom-control using antacids or H2-antagonists was the only option. Unfortunately, an increasing number of infected individuals are found to harbor bacteria resistant to first-line antibiotics. This results in initial treatment failure and requires additional rounds of antibiotic therapy.

Gastric cancer connection Gastric cancer (rare) and lymphoma have been associated with H. pylori, and the bacterium has been categorized as a group I carcinogen by the International Agency for Research on Cancer (IARC). However, it is not entirely clear that there is a causal relationship involved. Current scientific consensus is that "The effect of prevention or treatment of H. pylori infection on gastric cancer risk has not been studied adequately." (NIH 1994) The association is reasonably strong and it is certainly possible that H. pylori is involved as a causative agent in gastric cancer.

Genome studies of different strains Several strains are known, and the genomes of two have been completely sequenced. The Pylori Gene (http://genolist.pasteur.fr/PyloriGene/) website allows easy access to genome information for the H. pylori 26695 and H. pylori J99 strains. There are 62 genes in the "pathogenesis" category of this database. Both of these sequenced strains have an approximately 40 kb long Cag pathogenicity island (a common gene sequence believed responsible for pathogenesis) that contains over 40 genes. This pathogenicity island is usually absent from H. pylori strains isolated from humans who are carriers of H. pylori but remain asymptomatic.

Study of the H. pylori genome is centered on attempts to understand the ability of this organism to cause disease. The cagA gene codes for one of the major H. pylori virulence proteins. Bacterial strains that have the cagA gene are associated with an ability to cause severe ulcers. The cagA gene codes for a relatively long (1186 amino acid) protein. The CagA protein is transported into human cells where it may disrupt the normal functioning of the cytoskeleton. The Cag pathogenicity island has about 30 genes that code for a complex type IV secretion system. After attachment of H.pylori to stomach epithelial cells the CagA protein is injected into the epithelial cells by type IV secretion system. The CagA protein is phosphorylated on tyrosine residues by a host cell membrane-associated tyrosine kinase. Pathogenic strains of H. pylori have been shown to activate the epidermal growth factor receptor (EGFR), a membrane protein with a tyrosine kinase domain. Activation of the EGFR by H. pylori is associated with altered signal transduction and gene expression in host epithelial cells that may contribute to pathogenesis. It has also been suggested that a c-terminal region of the CagA protein (amino acids 873-1002) can regulate host cell gene transcription independent of protein tyrosine phosphorylation.

Legionella is a Gram negative bacterium, including many species that cause legionellosis or Legionaires' disease, most notably L. pneumophilia. At least 46 species and 70 serogroups have been identified. On the side-chains of the cell wall are carried the bases for the somatic antigen specifity of these organisms. The chemical composition of these side chains both with respect to components as well as arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are such important means of serologically classifying many Gram-negative.

At least 14 different serovars of L. pneumophila have been described as well as several other species being subdivided into a number of serovars. Sera have been used both for slide agglutination studies as well as for direct detection of bacteria in tissues using fluorescent-labelled antibody. Specific antibody in patients can be determined by the indirect fluorescent antibody test. ELISA and microagglutination tests have also been successfully applied.

Legionella pneumophila is non-acid, fast non-capsulated rods, aerobic and do not hydrolyse gelatin or produce urease. They are non-fermentative. L. pneumophila is neither pigmented nor does it autofluoresce. It is oxidase and catalase positive, produces beta-lactamase.

L. pneumophila is an intracellar pathogen. The internalisation of the bacteria is enhanced by the presence of antibody and complement. A pseudopod coils around the bacterium in this unique form of phagocytosis. Once internalised, the bacteria surround themselves by a membrane-bound phagolysosome. This becomes a vescicle, within which the bacteria multiply. They produce a 39kDa metalloprotease into culture fluids, which is cytotoxic for some cultured tissue culture cells.

The Methylococcaceae are a family of bacteria that obtain their carbon and energy from methane, called methanotrophs. They comprise the type I methanotrophs, in contrast to the Methylocystaceae or type II methanotrophs. They belong among the gamma subdivision of the Proteobacteria, and are typically given their own order.

The Methylococcaceae have internal membranes in the form of flattened discs, perpendicular to the cell wall. Methane is oxidized to give formaldehyde, which is fixed by a process called the RuMP cycle. Here formaldehyde is combined with the sugar ribose, producing hexulose. This in turn is broken down to produce glyceraldehyde, which is used to produce new ribose and other organic compounds. Catabolism does not involve a complete citric acid cycle.

The myxobacteria are a group of bacteria that predominantly live in the soil. The myxobacteria have very large genomes, relative to other bacteria, e.g. 9-10 million nucleotides. Sorangium cellulosum has the largest known (as of 2003) bacterial genome, at 12.2 million nucleotides. Myxobacteria are included among the proteobacteria, a large group of Gram-negative forms.

Myxobacteria can move actively by gliding. They typically travel in swarms, containing many cells kept together by intercellular molecular signals. This close concentration of cells may be necessary to provide a high concentration of extracellular enzymes used to digest food. Myxobacteria produce a number of biomedically and industrially useful chemicals, such as antibiotics, and export those chemicals outside of the cell.

When nutrients are scarce, myxobacteria cells aggregate by chemotaxis into fruiting bodies. These fruiting bodies can take different shapes and colors, depending on the species. Within the fruiting bodies, cells begin as rod-shaped vegetative cells, and develop into rounded myxospores with thick cell walls. These myxospores, analogously to spores in other organisms, are meant to survive until nutrients are more plentiful. The fruiting process is thought to benefit myxobacteria by ensuring that cell growth is resumed with a group (swarm) of myxobacteria, rather than as isolated cells. Similar life cycles have developed among certain amoebae, called cellular slime moulds.

The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera. Others are free-living, and include many of the bacteria responsible for nitrogen fixation. The group is defined mainly in terms of ribosomal RNA sequences, and is named for the Greek god Proteus, who could change his shape, because of the great diversity of forms found in it.

All Proteobacteria are Gram-negative, with an outer membrane mainly composed of liposaccharides. Many move about using flagella, but some are non-motile or rely on bacterial gliding. The last include the myxobacteria, a unique group of bacteria that can aggregate to form multicellular fruiting bodies. There is also a wide variety in the types of metabolism. Most members are anaerobic and heterotrophic, but there are numerous exceptions. A variety of forms, called purple bacteria are capable of producing energy through photosynthesis.

The proteobacteria are divided into five sections, referred to by the Greek letters alpha through epsilon, again based on RNA sequences. Some may be paraphyletic. These are often treated as classes. The currently recognized orders are listed at right, together with some representative genera. In addition to these, the mitochondria of eukaryotic cells, which conduct aerobic respiration, are derived from symbiotic proteobacteria, probably close relatives of rickettsias.

The Pseudomonadaceae are a family of bacteria, with two genera and the Azotobacter group. This group contains more named genera: Azomonas (motile, oval to spherical, do not produce cysts, and secrete large quantities of capsular slime), Azorhizophilus, and Azotobacter (usually motile, oval, or spherical bacteria, form thick-walled cysts, and may produce large quantities of capsular slime).

The bacterial genus Pseudomonas includes plant pathogenic bacteria such as P. syringae (various pathovars), the human pathogen P. aeruginosa, the ubiquitous soil bacterium P. putida, and some species that are known to cause problems in dairy products. However, the actions of this group of bacteria are mainly considered as beneficial or neutral to man. In recent times, members of the Pseudomonas have been used as biocontrol agents.

Members of Pseudomonas are Gram-negative, aerobic (able to consume oxygen) rods or cocci. They are flagellated so they can move around. Most produce a slime layer that cannot be phagocytosed, and which aids in the production of surface-colonising biofilms P. fluorescens is easily recognised as it secretes large amounts of fluorescent, yellow-green siderophores under iron-limited conditions. This species colonises plant roots. The opportunistic animal pathogen P. aeruginosa similarly secretes bright blue-green siderophores. Infection from it is usually accompanied by a "fruity" odor.

P. aeruginosa usually causes problems to humans who have already have had their immune systems weakened. This bacteria usually infects the urinary tract, burns, wounds, and also causes other blood infections. One in ten hospital acquired infections is from Pseudomonas. Cystic fibrosis patients are also predisposed to aeruginosa infection of the lungs.

Pseudomonas are able to grow in unexpected places. They have been found in areas where a lot of pharmaceuticals are prepared. Any carbon source, such as soap residue or cap liner adhesives is a suitable place for them to thrive. Other unlikely places where they have been found include antiseptics such as ammonium compounds and bottled mineral water. This ability to thrive in harsh conditions is a result of their hearty cell wall that contains porins. Their resistance to most antibiotics is attributed to their rapid efflux pumps which pump out the antibiotics before they are able to work.

Common hygiene practices should help to ward off any unwanted infections by this bacterium. If a more serious infection occurs, it can be treated with antibiotics such as piperacillin, imipenem, tobramycin, or ciprofloxacin, among others.

Vibrio cholerae is a rod-shaped bacterium that causes cholera in humans. It and other species of the genus Vibrio belong to the gamma subdivision of the Proteobacteria. There are two dominant strains, classic and El Tor. are in the O1 serogroup and both contain Inaba, Ogawa and Hikojima serotypes

It colonizes the gut, where it adheres to villous absorptive cells via filaments, and secretes a toxin, causing massive fluid and electrolyte loss by diarrhea.

Prokaryotes do not have a nucleus, mitochondria or any other membrane bound organelles. In other words neither their DNA nor any other of their metabolic functions are collected together in a discrete membrane enclosed area. Instead everything is openly accessible within the cell, though some bacteria have internal membranes as sites of metabolic activity these membranes do not enclose a separate area of the cytoplasm.

All the Prokaryotes (Bacteria and Archaea) are unicellular, only Eukaryotes:- the Protista, some Fungi and some Plants are multicellular. In most single celled organisms the cells are all the same most of the time in any given species. In multicellular organisms individual groups of cells have become specialised to perform particular roles in the life of the organism. The life of the organism is dependant on the correct working of all the different groups, each of which is dependant on all the others for its continued existence. In simple multicellular organisms such as sponges all the cells are very similar, in more complicated multicellular organisms the degree of specialisation of cells is much greater resulting in cells that are very different from one another. In humans, there are about 40 trillion cells all told. They occur in 1014 different types cells making up over 200 different kinds of tissues.

Cells are classified by fundamental units of structure and by the way they obtain energy. Cells are classified as prokaryotes or eukaryotes, which will be covered in more detail in the next two pages of this tutorial. Living things are classified in six kingdoms based on structure. Within prokaryotes, which appeared 3.5 billion years ago, are the kingdoms Monera (Eubacteria) and Archaea. Within eukaryotes, which evolved 1.5 billion years ago, are the kingdoms Protista, Plantae, Fungae, Animalia.

Cells are also defined according the need for energy. Autotrophs are "self feeders" that use light or chemical energy to make food. Plants are an example of autotrophs. In contrast, heterotrophs ("other feeders") obtain energy from other autotrophs or heterotrophs. Many bacteria and animals are heterotrophs.

Prokaryotes are single-celled organisms without a nucleus ; i.e. Bacteria and Archaea . This name comes from the Greek root karyon , meaning nut , combined with the prefix pro- , meaning before. Organisms composed of cells with a nucleus are called eukaryote s, where the prefix eu- means good or true . Prokaryotic life is ubiquitous on Earth, present in every conceivable biome (and also being found in places where no life of any kind had been expected to exist, for example the endolith ic biome). As such, there are prokaryotes with all manner of adaptations. Detailed treatments of prokaryotic structure can be found in the bacteria and archaea articles. It is thought that the first living cells on Earth were likely prokaryotic in structure, and possibly similar to some existing archaea. Fossil prokaryotes have been found in extremely ancient rocks on Earth. There was also a recent discovery of what may have been fossil prokaryotes in a Martian meteorite , though this has since been disputed.

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