What Is Biotechnology?

Biotechnology is technology based on biology, especially when used in agriculture, food science, and medicine.

Of the many different definitions available, the one formulated by the UN Convention on Biological Diversity is one of the broadest:

Biotechnology is any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use. One section of biotechnology is the directed use of organisms for the manufacture of organic products (examples include beer, milk-products, and skin). Naturally present bacteria are utilized by the mining industry in bioleaching. Biotechnology is also used to recycle, treat waste, clean up sites contaminated by industrial activities (bioremediation), and produce biological weapons.

There are also applications of biotechnology that do not use living organisms. Examples are DNA microarrays used in genetics and radioactive tracers used in medicine.

Modern biotechnology is often associated with the use of genetically altered microorganisms such as E. coli or yeast for the production of substances like insulin or antibiotics. It can also refer to transgenic animals or transgenic plants, such as Bt corn. Genetically altered Mammalian cells, such as Chinese Hamster ovarian cells, are also widely used to manufacture pharmaceuticals. Another promising new biotechnology application is the development of plant-made pharmaceuticals.

There are number of jargon terms for sub-fields of biotechnology.

Red biotechnology is biotechnology applied to medical processes. An example would include an organism designed to produce an antibiotic, or engineering genetic cures to diseases through genomic manipulation.

White biotechnology, also known as grey biotechnology, is biotechnology applied to industrial processes. An example would include an organism designed to produce a useful chemical. White biotechnology tends to consume less resources that traditional processes when used to produce industrial goods.

Green biotechnology is biotechnology applied to agricultural processes. An example would include an organism designed to grow under specific environmental conditions or in the presence (or absence) of certain agricultural chemicals. Green biotechnology tends to produce more environmentally friendly solutions then traditional industrial agriculture. An example of this would include a plant engineered to express a pesticide, thereby eliminating the need for external application of pesticides.

The term blue biotechnology has also been used to describe the marine and aquatic applications of biotechnology, but its use is relatively rare.

Biotechnology timeline:

8000BC Collecting of seeds for replanting. Evidence that Babylonians, Egyptians and Romans used selective breeding (artificial selection) practices to improve livestock.

6000BC Brewing beer, fermenting wine, baking bread with help of yeast

4000BC Chinese made yoghurt and cheese with lactic-acid-producing bacteria

1500 Plant collecting around the world

1800 Nikolai I. Vavilov created comprehensive research on breeding animals

1880 Microorganisms discovered

1856 Gregor Mendel started recombinant plant genetics

1919 Karl Ereky, a Hungarian engineer, first used the word biotechnology

1975 Method for producing monoclonal antibody developed by Kohler and Milstein

1980 Modern biotech is characterized by recombinant DNA technology. The prokaryote model, E. coli, is used to produce insulin and other medicine, in human form. (About 5% of diabetics are allergic to animal insulins available before)

1992 FDA approves of the first GM food from Calgene: "flavor saver" tomato

2000 Completion of the Human Genome Project

Industrial biotechnology (also known as white biotechnology) is the practice of using cells to generate industrially-useful products. The Economist speculated (as cited in the Economist article listed in the "References" section) industrial biotechnology might significantly impact the chemical industry. The Economist also suggested it might enable economies to become less dependent on fossil fuels.

Diversa is an example of a company that specializes in industrial biotechnology.

Bioremediation can be defined as any process that uses microorganisms or their enzymes to return the environment altered by contaminants to its original condition. Bioremediation may be employed in order to attack specific contaminants, such as chlorinated pesticides that are degraded by bacteria, or a more general approach may be taken, such as oil spills that are broken down using multiple techniques including the addition of fertilizer to facilitate the decomposition of crude oil by bacteria.

Not all contaminants are readily treated through the use of bioremediation; for example, heavy metals such as cadmium and lead are not readily absorbed or captured by organisms. The integration of metals such as mercury into the food chain may make things worse as organisms bioaccumulate these metals.

However, there are a number of advantages to bioremediation, which may be employed in areas which cannot be reached easily without excavation. For example, hydrocarbon spills (or more specific: gasoline) may contaminate groundwater well below the surface of the ground; injecting the right organisms, in conjunction with oxygen-forming compounds, may significantly reduce concentrations after a period of time. This is much less expensive than excavation followed by burial elsewhere or incineration, and reduces or eliminates the need for pumping and treatment, which is a common practice at sites where hydrocarbons have contaminated groundwater.

Generally, bioremediation technologies can be classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site while ex situ involves the removal of the contaminated material to be treated elsewhere. Some examples of bioremediation technologies are bioventing, land farming, bioreactor, composting, bioaugmentation and biostimulation.

A bioreactor is a vessel in which is carried out a chemical process which involves organisms or biochemically active substances derived from such organisms.

Bioreactors are commonly cylindrical, ranging in size from some liter to cube meters,and are often made of stainless steel.

Bioreactor design Bioreactor design is quite a complex engineering task. Under optimum conditions the microorganisms or cells will reproduce at an astounding rate. The vessel's environmental conditions like gas (i.e., air, oxygen, nitrogen, carbon dioxide) flowrates, temperature, pH and dissolved oxygen levels, and agitation speed need to be closely monitored and controlled. One bioreactor manufacturer, Broadley-James Corporation, uses vessels, sensors, controllers, and a control system, digitally networked together for their bioreactor system.

Fouling can harm the overall sterility and efficiency of the bioreactor, especially the heat exchangers. To avoid it the bioreactor must be easily cleanable and must be as smooth as possible (therefore the round shape).

Heat exchange is needed to maintain the bioprocess at a constant temperature. Biological fermentation is a major source of heat, therefore in most cases bioreactors need water refrigeration. They can be refrigerated with an external jacket or, for very large vessels, with internal coils.

Optimal oxygen transfer is perhaps the most difficult task to accomplish. Oxygen is poorly soluble in water -and even less in fermentation broths- and is relatively scarce in air (20.8%). Oxygen transfer is usually helped by agitation, that is also needed to mix nutrients and to keep the fermentation homogeneous. There are however limits to the speed of agitation, due both to high power consumption (that's proportional to the cube of the speed) and the damage to organisms due to excessive tip speed.

Compost is the decomposed remnants of organic materials (those with plant and animal origins). Compost is used in gardening and agriculture, mixed in with the soil. It improves soil structure, increases the amount of organic matter, and provides nutrients.

Compost is a common name for humus, which is the result of the decomposition of organic matter. Decomposition is performed primarily by microbes, although larger creatures such as worms and ants contribute to the process. Decomposition occurs naturally in all but the most hostile environments, such as buried in landfills or in extremely arid deserts, which prevent the microbes and other decomposers from thriving.

Composting is the controlled decomposition of organic matter. Rather than allowing nature to take its slow course, a composter provides an optimal environment in which decomposers can thrive. To encourage the most active microbes, the compost pile needs the proper mix of the following ingredients: Carbon Nitrogen Oxygen (air) Water. Decomposition happens even in the absence of some of these ingredients, but not nearly as quickly and not nearly as pleasantly (for example, the plastic bag of vegetables in your refrigerator is decomposed by microbes, but the absence of air encourages anaerobic microbes that produce disagreeable odors).

All guidelines for building compost piles have the goal of creating the proper environment for a decomposing ecosystem. The ecosystem in a compost pile is a microcosm of larger ecosystems. The correct environment must be maintained for a healthy and vigorous community of decomposers. In addition to the decomposers that work directly on the organic content of the pile, compost piles provide habitat for those that prey upon direct decomposers. Their waste also becomes part of the process.

The most effective decomposers are bacteria and other microorganisms. Also important are fungi, molds, protozoa, and actinomycetes--which is something between a fungus and a mold and is often seen as white filaments in decomposing organic matter. At a macroscopic level, earthworms, ants, snails, slugs, millipedes, sow bugs, springtails, and others work on consuming and breaking down the organic matter. Centipedes and other predators feed upon these decomposers.

Compost ingredients The goal in a compost pile is to provide a healthy environment--and nutrition--for the rapid decomposers, the bacteria.

The most rapid composting occurs with the ideal ratio--by dry chemical weight--of carbon to nitrogen, from 25-to-1 to 30-to-1. In other words, the ingredients placed in the pile should contain 30 times as much carbon as nitrogen. For example, grass clippings average about 19-to-1 and dry autumn leaves average about 55-to-1. Mixing equal parts by volume approximates the ideal range. Commercial-grade composting operations pay strict attention to this ratio. For backyard composters, however, the charts of carbon and nitrogen ratios in various ingredients and the calculations required to get the ideal mixture can be intimidating, so many rules of thumb exist to guide composters in approximating this mixture.

High-carbon sources provide the cellulose needed by the composting bacteria for conversion to sugars and heat.

High-nitrogen sources provide the most concentrated protein, which allow the compost bacteria to thrive.

Some ingredients with higher carbon content:

Dry, straw-type material, such as cereal straws Autumn leaves Sawdust and wood chips Some paper and cardboard (such as corrugated cardboard or newsprint with soy-based inks) Some ingredients with higher nitrogen content:

Wilted green material (usually crop residues, or plants mowed for the purpose) Animal manures (vegetarians, not meat-eaters) Grass clippings Fruit and vegetable trimmings, skins, and waste Poultry manure provides lots of nitrogen but little carbon. Horse manure provides both. Sheep and cattle manure don't drive the compost heap to as high a temperature as poultry or horse manure, so the heap takes longer to produce the finished product.

In an attempt to judge the proper mix of materials, different rules of thumb are available. Some prefer to add one basket full of nitrogen source followed by one basket of carbon source. Mixing the materials as they are added increases the rate of decomposition, but some people prefer to place the materials in alternating layers, approximately 15 cm (6 inches) thick, to help estimate the quantities. Keeping carbon and nitrogen sources separated in the pile can slow down the process but decomposition will occur in any event.

Composting techniques There are two primary methods of aerobic composting:

Active (or hot) composting, which allows the most effective decomposing bacteria to thrive, kills most pathogens and seeds, and rapidly produces usable compost Passive (or cold) composting, which lets nature take its course in a more leisurely manner and leaves many pathogens and seeds dormant in the pile Most commercial and industrial composting operations use active composting techniques. This ensures a higher quality product and produces results in the shortest time (SEE compost windrow turner).

Home composters use a range of techniques varying from extremely passive composting (throw everything in a pile in a corner and leave it alone for a year or two) to extremely active (monitoring the temperature, turning the pile regularly, and adjusting the ingredients over time) and combinations of both.

Some composters use mineral powders to absorb smells, although a well-maintained pile seldom has bad odors.

Microbes and heating the pile An effective compost pile is kept about as damp as a well wrung-out sponge. This provides the moisture that all life needs to survive; in a compost pile, it provides an environment in which microbes can begin to do their work. Bacteria and other microorganisms fall into a variety of groups in terms of what their ideal temperature is and how much heat they generate as they do their work. Mesophilic bacteria enjoy midrange temperatures, from about 20 to 40 °C (70 to 110 °F). As they decompose the organic matter, they generate heat, and the inner part of a compost pile heats up the most.

The heap should be about 1 m (3 ft) wide, 1 m (3 ft) tall, and as long as is practicable – the advantage to making the heap at least 1 m³ (1 yd³) is that it provides suitable insulating mass to allow a good heat build-up as the material decays. The ideal temperature range hovers around 60 °C (140 °F), which kills most pathogens and weed seeds and also provides a suitable environment for thermophilic (heat-loving) bacteria, which are the fastest acting decomposers. The centre of the heap should get quite warm, possibly hot enough to burn a bare hand. If this fails to happen, common reasons include the following:

The heap is too wet, thus excluding the oxygen required by the compost bacteria The heap is too dry, so that the bacteria do not have the moisture needed to survive and reproduce There is insufficient protein (nitrogen rich material) The solution is to add material, if necessary, and/or to turn the pile to aerate it.

Depending on how quickly the compost is required, the heap can be turned one or more times to bring the outer layers to the inside of the heap and vice versa, as well as to aerate the mixture. Adding water at this time keeps the pile as damp as a wrung-out sponge. One guideline is to turn the pile when the high temperature has begun to drop, indicating that the food source for the fastest-acting bacteria (in the center of the pile) has been largely consumed. After the temperature stops rising after the pile has been turned, there is no further advantage in turning the pile. When all the material has become barely recognisable from the original ingredients, turning into dark brown or nearly black crumbly matter, it's ready to use. Some practitioners like to leave the compost to mature further for up to a year as this seems to make the benefits of compost last longer.

Other ingredients Some like to put special materials and activators into their compost. A light dusting of agricultural lime (not on the animal manure layers) can curb excessive acidity that can slow down the fermentation. Seaweed meal can provide a ready source of trace elements. Finely pulverised rock dust can also provide needed minerals, but watch out for rock dust that consists mostly of clay.

The animal manure part of compost source materials can be collected by composting toilets (in this case, human feces). However, such compost is usually not used as a fertilizer for plants that are directly edible (e.g., salad crops) but should instead be used on trees, bush fruits or else on the ornamental garden.

Bioaugmentation refers to the introduction of a group of natural microbial strain or a genetically engineered variant so as to achive bioremediation.

Usually the step involves studying the indigenous varieties present in the location. If the indigenous variety do not have the metabolic machinery that can do the remediation process, exogenous varieties with such sophisticated pathways are introduced.

Remediation is the removal of pollution or contaminants from land (including sediments in waterways) for the general protection of the environment or, quite commonly, from a brownfield site so that it can be reused. The reuse of brownfield sites is part of the urban consolidation movement and allows the regeneration of decaying former industrial areas, sometimes for industry, but often for high density housing, particulalry in areas of scenic beauty (along Harbours and rivers) and close to the CBD of a city or major transport infrastructure such as railway stations.

Remediation is generally subject to an array of legislation, and is based on assessments of health and ecological risks where there are no legislated standards or where standards are advisory (often called preliminary remediation goals (PRG)s).

Remediation in terms of new media, is the representation of one medium in another. (Jay David Bolter and Richard Grusin 1999).

Remediation standards In the USA the most comprehensive set of PRG's is from the EPA Region 9, although the Canadian EPA also has a comprehensive spreadsheet of PRG's. There is also a set of standard used in Europe commonly called the Dutch standards. The EU is rapidly moving towards European wide standards, although most of the industrialised nations in Europe have their own standards at present

Site assessment Once a site is suspected of being seriously contaminated there is a need to assess it. The historical use of the site and the materials used and produced on site will guide the assessment strategy and nature of sampling and chemical testing to be done. Often nearby sites owned by the same company or which are nearby and have been reclaimed, levelled or filled are also contaminated even where the current land use seems innocuous. For example, the car park may have been levelled by using contaminated waste in the fill. It is also important to consider off site contamination or nearby sites often through decades of emissions to soil, water, and air. Ceiling dust, topsoil, surface and groundwater of nearby properties should be tested both before and after the remediation. This is a controversial step as:

No one wants to have to pay for the clean up of the site; If nearby properties are found to be contaminated it may have to be noted on their property title, potentially affecting saleability or value; No one wants to pay for the cost of assessment. Often corporations which do voluntary testing of their sites are protected from the reports to environmental agencies becoming public under Freedom of Information Acts, however a Freedom Of Information inquiry will often produce other documents that are not protected or will produce references to the reports.

Funding remediation In the US there has been a mechanism for taxing polluting industries to form a Superfund to remediate abandoned sites, or to litigate to force corporations to remediate their contaminated sites. Other countries have other mechanisms and commonly sites are rezoned to "higher" uses such as high density housing, to give the land a higher value so that after deducting clean up costs there is still an incentive for a developer to purchase the land, clean it up, redevelop it and sell it on, often as apartments (home units).

Remediation technologies Remediation technologies are many and varied. The best source of information is probably http://www.clu-in.org/

Some technologies are controversial, particularly anything involving relative low temperature incineration because of the risks of dioxins released in the atmosphere through the exhaust gases. For this reason remediation proponents often use terminolgy like thermal oxidiser and direct thermal desorption to minimise the risk of the community thinking about incineration risks. However, controlled, high temperature incineration with filtering of exhaust gases should not pose any risks.

The treatment of environmental problems through biological means is known as bioremediation and the specific use of plants is known as phytoremediation.

Community consultation and information In preparation for any significant remediation there should be extensive community consultation. The proponent should both present information to and seek information from the community. The proponent needs to know about "sensitive" (future) uses like childcare, schools, hospitals, and playgrounds as well as community concerns and interests information. Consultation should be open, on a group basis so that each member of the community is informed about issues they may not have individually thought about. An independent chairperson acceptable to both the proponent and the community should be engaged (at proponent expense if a fee is required). Minutes of meetings including questions asked and the answers to them and copies of presentations by the proponent should be available both on the internet and at a local library (even a school library) or community centre.

Incremental health risk Incremental Health Risk is the increased risk that a receptor (normally a human being living nearby) will face from (the lack of) a remediation project. The use of incremental health risk is based on cancer and non-cancer effects such as reproductive abnormalities and often involves value judgements about the acceptable projected rate of increase in cancer. In some jursdictions this is 1 in a million, but in other jurisdictions it is 1 in 100,000. A relatively small incremental health risk from a single project is not of much comfort if the area already has a relatively high health risk from other operations like incinerators or other emissions, or if there are other projects at the same time causing a greater cumulative risk or an unacceptably high total risk. An analogy often used by remediators is to compare the risk of the remediation on nearby residents to the risks of death through car accidents or tobacco smoking.

Emissions standards Standards are set for the levels of dust, noise, odour, emissions to air and groundwater, and discharge to sewer or waterways of all chemicals of concern or chemicals likely to be produced during the remediation by processing of the contaminants. These are compared against both natural background levels in the area and standards for areas zoned as nearby areas are zoned and against standards used in other recent remediations. Just because the emission is emanating from an area zoned industrial doesn't mean that in a nearby residential area there should be permitted any exceedences of the appropriate residential standards.

Monitoring for compliance against each standards is critical to ensure that exceedences are detected and reported both to authorities and the local community.

Enforcement is necessary to ensure that continued or significant breeches result in fines or even a jail sentence for the remediator.

Penalties must be significant as otherwise fines are treated as a normal expense of doing business. It must be cheaper to comply than have continuous breeeches.

Transport and emergency safety assessment Assessment should be made of the risks of operations, transporting contaminated material, disposal of waste which may be contaminated including workers clothes, and a formal emergency response plan should be developed. Every worker and visitor entering the site should have a safety induction tailored to their involvement with the site.

Impacts of funding remediation The rezoning is often resisted by local communities and local government because of the adverse impacts on the local amenity of the remediation and the new development. The main impacts during remediation are noise, dust, odour and incremental health risk. Then there is the noise dust and traffic of developments. Then there is the impact on local traffic, schools, playing fields, and other public facilities of the often vastly increased local population.

Example of a major remediation project For an example of a complete rezoning by a state government over the opposition of local government and local communities of former chemical plants to fund remediation to allow for redevelopment for high density residential, retail and office development in Australia see http://rhodesnsw.org

In this case the proposed rezoning, remediation and redevelopment has a wealth of material available through the internet from:

list of sources of publicly available material, most accessible through the internet and from http://rhodesnsw.org: Numerous investigations and reports by Australian and International consultants For the former Union Carbide site, a previous remediation by excavation and containment in a clay capped sarcophagus, separated from the Bay by a bentonite wall. A Parliamentary Inquiry by the Upper House of the Parliament of New South Wales, a state of Australia; Two Commissions of Inquiry, one for each of the major dioxin contaminated sites, both contaminated by the operations of Union Carbide; Resolutions by the relevant local government bodies (originally Concord council and after the Municipality of Concord was merged with Drummoyne Council to form the City of Canada Bay, by that Council); Campaigns by local residents' groups, Greenpeace Australia, Nature Conservation Council of NSW, and Inner West (of Sydney branch of the) Greens published submissions by Planning NSW and Environmental Protection Agency of NSW; Comprehensive Environmental Impact studies published in digital format and available on CD from Planning NSW. This rezoning, remediation and redevelopment of land contaminated by Union Carbide, ICI and others also involves the remediation of a strip of dioxin contaminated sediments in Homebush Bay, New South Wales. The Homebush Bay area was home to the main events of the Sydney 2000 Summer Olympics. The sediments were dealt with in the Commission of Inquiry into the Lednez site formerly owned by Union Carbide, but not to the satisfaction of local community activists.

The remediation of Homebush Bay is important because of its impact on the food chain which extends through benthos not only to local protected and threatened species of birds, but also to JAMBA and CAMBA protected species and species which use other RAMSAR protected wetlands. Ultimately human health is impacted through the food chain. Homebush Bay has a complete fishing ban, there is a commercial fin fishing ban west of the Gladesville Bridge, and based on submissions of the remediator and NSW Waterways and EPA the complete fishing ban ought be extended to the whole of the Parramatta River west of Homebush Bay and at least as far East as the Ryde Traffic Bridge.

Phytoremediation is the technical term used to describe the treatment of environmental problems through the use of plants.

Certain plants are able to extract hazardous substances such as arsenic, lead and uranium from soil and water. One example is alpine pennycress, a plant which naturally accumulates high levels of cadmium and zinc from the environment. Alpine pennycress is therefore known as a hyperaccumulator of these metals, which in unnaturally high levels would be poisionous to many plants. Another example of a hyperaccumulator is the brake fern. This fern extracts arsenic from the soil at a much greater rate than other plants.

This has been done successfully in clinical trials, particularly in the case of Ashanti DeSilva, a girl who had a defective gene that was responsible for the immune system enzyme ADA. Thus she was prone to infections. Scientists took out her white blood cells and used a delivery system to inject a functional ADA gene into the cells. These were injected back into Ashanti's arm. a, f. Now she takes only a small "backup" dose of what would have been a battery of preventive medicines for maintaining her healthy state.

This arsenic is stored in the fern's leaves at as much as 200 times that present in the soil, thus enabling effective and practical clean-up programs. Sunflowers were also used to clean up uranium near Chernobyl.

Breeding programs and genetic engineering are powerful methods for enhancing natural tendencies of plant, or for introducing these tendencies into alternative types of plant which might be more suitable for the environmental conditions.

The range of biological treatments for environmental problems, as described by the term phytoremediation, actually consists of several specific processes:

Phytoextraction - Uptake of substances from the environment, with storage in the plant (phytoaccumulation). Phytostabilisation - Reducing the movement or transfer of substances in the environment. For example, limiting the leaching of substances contaminating soil. Phytostimulation - Enhancement of microbial activity for the degradation of contaminants, typically around plant roots. Phytotransformation - Uptake of substances from the environment, with degradation occurring within the plant (phytodegradation). Phytovolatilization - Removal of substances from the soil or water with release into the air, possibly after degradation. Rhizofiltration - The removal of toxic metals from ground water.

Bioleaching is the extraction of specific metals from their ores through the use of bacteria.

Bioleaching is a new technique used by the mining industry to extract minerals such as gold and copper from their ores. Traditional extractions involve many expensive steps such as roasting and smelting, which requires sufficient concentrations of elements in ores. Low concentrations are not a problem for bacteria because they simply ignore the waste which surrounds the metals, attaining extraction yields of over 90% in some cases. These microorganisms actually gain energy by breaking down minerals into their constituent elements. The company simply collects the ions out of solution after the bacteria have finished.

Some advantages associated with bioleaching are:

economical: bioleaching is generally simpler and therefore cheaper to operate and maintain than traditional processes, since fewer specialists are needed to operate complex chemical plants. environmental: The process is more environmentally friendly than traditional extraction methods. For the company this can translate into profit, since the necessary limiting of sulfur dioxide emissions during smelting is expensive. Less landscape damage occurs, since the bacteria involved grow naturally, and the mine and surrounding area can be left relatively untouched. As the bacteria breed in the conditions of the mine, they are easily cultivated and recycled. Some disadvantages associated with bioleaching are:

not economical: the bacterial leaching process is very slow compared to smelting. This brings in less profit as well as introducing a significant delay in cash flow for new plants. not environmental: Toxic chemicals are sometimes produced in the process. Sulfuric acid and H+ ions formed can leak into the ground and surface water turning it acidic, causing environmental damage. Heavy ions such as iron, zinc, and arsenic leak during acid mine drainage. When the pH of this solution rises, as a result of dilution by fresh water, these ions precipitate, forming "Yellow Boy" pollution. For these reasons, setup of bioleaching must be carefully planned, since the process can lead to biosafety failure. f, i, a. Currently it is more economical to smelt copper ore rather than to use bioleaching, since the concentration of copper in its ore is generally quite high. The profit obtained from the speed and yield of smelting justifies its cost. However, the concentration of gold in its ore is generally very low. The cheaper cost of bacterial leaching in this case outweighs the time it takes to extract the metal.

Bacteria (singular, bacterium) are a major group of living organisms. They are microscopic and mostly unicellular, with a relatively simple cell structure lacking a cell nucleus, cytoskeleton, and organelles such as mitochondria and chloroplasts. Such organisms are called prokaryotes, in contrast to organisms with more complex cells, called eukaryotes. The term bacteria has variously applied to all prokaryotes or to a major group of them, depending on ideas about their relationships.

abundant of all organisms. They are ubiquitous in soil, water, and as symbionts of other organisms. Many pathogens, including those responsible for many if not most non-hereditary diseases, are bacteria. Most are minute, usually only 0.5-5.0 μm in size, though one type may reach 0.3 mm in diameter (Thiomargarita). They generally have cell walls, like plant and fungal cells, but with a very different composition (peptidoglycans). Many move around using flagella, which are different in structure from the flagella of other groups.

The first bacteria were observed by Antony van Leeuwenhoek in 1683 using a single-lens microscope of his own design. The name bacterium was introduced much later, by Ehrenberg in 1828, derived from the Greek word βακτηριον meaning "small stick". Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described the role of bacteria as conveyors and causes of disease or pathogens.

Originally the bacteria were considered microscopic fungi (called Schizomycetes), except for the photosynthetic cyanobacteria, which were considered a group of algae (called Cyanophyta or blue-green algae). It was only with the study of detailed cell structure that it was realized they formed a fundamental group, separate from the other organisms. In 1956 Copeland gave them their own kingdom Mychota, later renamed Monera, Prokaryota, or Bacteria. During the 1960s the concept was refined and bacteria (now including cyanobacteria) were recognized as one of two major divisions of the living world, together with the eukaryotes. Eukaryotes were generally believed to have evolved from bacteria, later from assemblies of bacteria.

The advent of molecular systematics challenged this view. In 1977, Woese divided the prokaryotes into two groups based on 16S rRNA sequences, called the kingdoms Eubacteria and Archaebacteria. He argued that each of these and the eukaryotes all evolved separately and in 1990 emphasized this by promoting them to domains, which were renamed the Bacteria, Archaea, and Eucarya. This redefinition has generally been accepted by molecular biologists but criticized by some others, who maintain that he over-emphasized a few genetic differences and that both archaebacteria and eukaryotes probably developed from within the eubacteria.

Reproduction Bacteria reproduce only asexually, not sexually. Specifically they reproduce by binary fission, or simple cell division. During this process, one cell divides into two daughter cells with the development of a transverse cell wall.

However, independent of sexual reproduction, genetic variations can occur within individual cells through recombinant events such as mutation (random genetic change within a cell's own genetic code). Similar to more complex organisms, bacteria also have mechanisms for exchanging genetic material. Although not equivalent to sexual reproduction, the end result is that a bacterium contains a combination of traits from two different parental cells. Three different modes of exchange have thus far been identified in bacteria:

transformation (the transfer of naked DNA from one bacterial cell to another in solution, this can include dead bacteria), transduction (the transfer of viral, bacterial, or both bacterial and viral DNA from one cell to another via bacteriophage) and; bacterial conjugation (the transfer of DNA from one bacterial cell to another via a special protein structure called a conjugation pilus). Bacteria, having acquired DNA from any of these events, can then undergo fission and pass the recombined genome to new progeny cells. Many bacteria harbor plasmids that contain extrac