What is Food Microbiology?

The focus of Food Microbiology is on the detection and analysis of foodborne spoilage microorganisms.

Food microbiology is the study of food micro-organisms; how we can identify and culture them, how they live, how some infect and cause disease and how we can make use of their activities.

Microbes are single-cell organisms so tiny that millions can fit into the eye of a needle.

They are the oldest form of life on earth. Microbe fossils date back more than 3.5 billion years to a time when the Earth was covered with oceans that regularly reached the boiling point, hundreds of millions of years before dinosaurs roamed the earth.

The field of food microbiology is a very broad one, encompassing the study of microorganisms which have both beneficial and deleterious effects on the quality and safety of raw and processed foods.

Food science is a discipline concerned with all aspects of food - beginning after harvesting, and ending with consumption by the consumer. It is considered one of the agricultural sciences, and it is a field which is entirely distinct from the field of nutrition. In the U.S., food science is typically studied at land-grant universities.

Examples of the activities of food scientists include the development of new food products, design of processes to produce these foods, choice of packaging materials, shelf-life studies, sensory evaluation of the product with potential consumers, microbiological and chemical testing. Food scientists in universities may study more fundamental phenomena that are directly linked to the production of a particular food product.

Food scientists are generally not directly involved with the creation of genetically modified (bio-engineered) foods.

Some of the subdisciplines of food science: Food safety, Food engineering, Product development, Sensory analysis, Food chemistry.

The primary tool of microbiologists is the ability to identify and quantitate food-borne microorganisms; however, the inherent inaccuracies in enumeration processess, and the natural variation found in all bacterial populations complicate the microbiologists job.

Without microbes, we couldn’t eat or breathe.

Without us, they’d probably be just fine.

Understanding microbes is vital to understanding the past and the future of ourselves and our planet.

Archaea look and act a lot like bacteria. So much so that until the late 1970s, scientists assumed they were a kind of “weird” bacteria.

Then microbiologist Carl Woese devised an ingenious method of comparing genetic information showing that they could not rightly be called bacteria at all. Their genetic recipe is too different.

So different Woese decided they deserved their own special branch on the great family tree of life, a branch he dubbed the Archaea.

Archaea comes from the Greek word meaning “ancient.” An appropriate name, because many archaea thrive in conditions mimicking those found more than 3.5 billion years ago. Back then, the earth was still covered by oceans that regularly reached the boiling point — an extreme condition not unlike the hydrothermal vents and sulfuric waters where archaea are found today.

Some scientists consider archaea living fossils that may provide hints about what the earliest life forms on Earth were like, and how life evolved on our planet.

In addition to superheated waters, archaea have been found in acid-laden streams around old mines, in frigid Antarctic ice and in the super-salty waters of the Dead Sea. A number of other extreme-living bacterial species also enjoy these conditions, too, such as the community of cyanobacteria and bacteria shown top right.

Foodborne illness or food poisoning is caused by consuming food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites. Such contamination usually arises from improper handling, preparation or storage of food. Foodborne illness can also be caused by adding pesticides or medicines to food, or by accidentally consuming naturally poisonous substances like poisonous mushrooms or reef fish. Contact between food and pests, especially flies, rodents and cockroaches, is a further cause of contamination of food.

Some common diseases are occasionally foodborne mainly through the water vector, even though they are usually transmitted by other routes. These include infections caused by Shigella, Hepatitis A, and the parasites Giardia lamblia and Cryptosporidium parvum.

• Thermophiles like unusually hot temperatures. A few species have been found to survive even above 110 degrees Celsius (water boils at 100 degrees Celsius). • Psychrophiles like extremely cold temperatures (even down to -10 degrees Celsius). • Halophiles thrive in unusually salty habitats. Some can thrive in water that’s 9% salt; sea water contains only 0.9% salt. • Acidophiles prefer acidic conditions; Alkaliphiles prefer very alkaline environs.

Accumulating sufficient data on the behaviour of microorganisms in foods requires an extensive amount of work, and is costly. In addition, while data alone can describe the response of a microorganisms in food, they provides little insight into the relationship between physiological processes and growth or survival.

Scientists also use molecular tools to extract and compare bits of a particular kind of RNA from samples in order to determine if previously known or new microbes are present in a particular environment. This technique is widely used as a biomarker and for microbial ecology studies. It uses a particular kind of RNA known as 16S ribosomal RNA, or 16S rRNA.

Ribosomes are the gene-translating machines in all living things. When a gene on a piece of DNA is copied into a strand of messenger RNA and ferried out of the cell nucleus into the cell fluid, ribosomes there latch onto this mRNA. The ribosomes move along the mRNA strand, reading the code contained in its sequence of nucleotide bases (the As, Gs, Cs and Us, since U replaces T in RNA) and stringing the right amino acids together based on the code to build protein chains.

Pasteurization is typically associated with milk. There are two widely used methods to pasteurize milk: high temperature/short time (HTST), and ultra-high temperature (UHT). HTST is by far the most common method. Milk simply labelled "pasteurized" is usually treated with the HTST method, whereas milk labelled "ultra-pasteurized" must be treated with the UHT method. HTST involves holding the milk at a temperature of 161.5 degrees F (or 72 C) for at least 15 seconds. UHT involves holding the milk at a temperature of 280 degrees F (or 138 C) for at least two seconds.

Pasteurization methods are usually standardized and controlled by national food safety agencies (such as the USDA in the United States and the Food Standards Agency in the U.K.). These agencies require milk to be HTST pasteurized in order to qualify for the "pasteurized" label. There are different standards for different dairy products, depending on the fat content and the intended usage. For example, the pasteurization standards for cream differ from the standards for fluid milk, and the standards for pasteurizing cheese are designed to preserve the phosphatase enzyme, which aids in curing the cheese.

The HTST pasteurization standard was designed to achieve a 5-log (approximately one million-fold) reduction in the number of viable microorganisms in milk. This is considered adequate for destroying almost all yeasts, mold, and common spoilage bacteria and also to ensure adequate destruction of common pathogenic heat-resistant organisms (including particularly Mycobacterium tuberculosis, which causes tuberculosis and Coxiella burnetii, which causes Q fever). HTST pasteurization processes must be designed so that the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.

HTST pasteurized milk typically has a refrigerated shelf life of two to three weeks, whereas ultra pasteurized milk can last much longer when refrigerated, sometimes two to three months. When UHT pasteurization is combined with sterile handling and container technology, it can even be stored unrefrigerated for long periods of time.

The genes for ribosomal RNA have changed little over millions of years as organisms evolved. The slight changes that have occurred provide clues as to how closely or distantly various organisms are related.

Because the 16S rRNA gene is very short, just 1,542 nucleotide bases, it can be quickly and cheaply copied and sequenced. So when a scientist has a test tube full of pond water or dirt from an arid mountainside, she must first pull out the rRNA that’s mixed up with all the other RNA, DNA and other stuff in that tube. To do this, she cleans and purifies the sample first, getting rid of unwanted debris.

She then uses one or several techniques designed to break open cells like a kid cracking open a piggybank. Now she has to find the 16S rRNA genes in and amongst all the other genes. Although 16S rRNA genes from different microbes will have a few different nucleotides scattered throughout the sequences, those nucleotides at the very beginning or end of the gene are the same from organism to organism.

The scientist uses several copies of another bit of RNA called a primer. A primer is like a mirror image of a short bit of RNA or single strand of DNA; that is, its sequence of nucleotides is the direct complement to the sequence of nucleotides in a known part of the target RNA or DNA.

In this instance, the primer would be the mirror image of the beginning or end of the 16S rRNA sequence. Because complementary nucleotides pair up like the two halves of Velcro, the primer enables the scientist to pick out the 16S rRNA in the sample. The scientist then uses PCR to make millions of copies of these genes. She then has enough 16S rRNA to compare the sequences of the genes from her sample to libraries of stored 16S rRNA genes from numerous known bacteria.

If some of her gene sequences match up perfectly, she knows that these are microbes that have been previously identified. But if others among her sampled sequences show differences, she knows she has found previously unknown microbes.

Bacteria can be found virtually everywhere. They are in the air, the soil, and water, and in and on plants and animals, including us. A single teaspoon of topsoil contains about a billion bacterial cells (and about 120,000 fungal cells and some 25,000 algal cells). The human mouth is home to more than 500 species of bacteria.

Some bacteria (along with archaea) thrive in the most forbidding, uninviting places on Earth, from nearly-boiling hot springs to super-chilled Antarctic lakes buried under sheets of ice. Microbes that dwell in these extreme habitats are aptly called extremophiles.

Like dinosaurs, bacteria left behind fossils. The big difference is that it takes a microscope to see them. And they are older.

Bacteria and their microbial cousins the archaea were the earliest forms of life on Earth. And may have played a role in shaping our planet into one that could support the larger life forms we know today by developing photosynthesis.

Cyanobacteria fossils date back more than 3 billion years. These photosynthetic bacteria paved the way for today's algae and plants. Cyanobacteria grow in the water, where they produce much of the oxygen that we breathe. Once considered a form of algae, they are also known as blue-green algae.

The human body consists of millions of different cells. A bacterium consists of a single cell.

A bacterium’s genetic information is contained in a single DNA molecule suspended in a jelly-like substance called cytoplasm. In most cases, this and other cell parts are surrounded by a flexible membrane that is itself surrounded by a tough, rigid cell wall. A few species, such as the mycoplasmas, don’t have cell walls.

Even though bacteria have only one cell each, they come in a wide range of shapes, sizes, and colors.

Does a bacterium’s cell wall, shape, way of moving, and environment really matter?

Yes! The more we know about bacteria, the more we are able to figure out how to make microbes work for us or stop dangerous ones from causing serious harm. And, for those of us who like to ponder more philosophical questions like the origins of the Earth, there may be some clues there as well.

Whether a bacteria has a thin or a thick cell wall determines what antibiotic will work against it. If you’ve ever been sick and waited for the results of a culture and sensitivity test, you may have heard the terms “Gram-positive” or “Gram-negative.”

Bacteria with thick cell walls retain dye from a cell-staining method developed by Christian Gram; bacteria with thin walls do not. Knowing the difference can and does save lives, time and money, and ensures that you or your loved one is getting the best and most effective treatment.

Some bacteria look like little balls (Micrococcus) while others appear like tangled strings or corkscrews (Leptospira) under a microscope. Others look like medicine capsules (Salmonella) or segmented ribbons (Cyanobacteria) or sticks. Still others look like fat commas (Vibrios).

Some bacteria are stalked (Caulobacter) while others have buds (Rhodomicrobium). Some have sheaths (Sphaerotilus) while others don’t.

Bacteria like mycoplasmas that lack a hard cell wall don’t have any particular shape at all.

Just like in animals, where size ranges from the giant blue whale to the tiny gnat, bacteria vary from 1 millimeter in diameter at the largest end of the scale to 20 nanometers in length at the smallest.

The largest bacteria found so far can actually be seen without the use of a microscope (Thiomargarita namibiensis and Epulopiscium fischelsoni). The smallest known bacteria are so tiny that they were once thought to be viruses (Mycoplasmas).

Some bacteria have hair- or whip-like appendages called flagella used to ‘swim’ around. Others produce thick coats of slime and ‘glide’ about. Some stick out thin, rigid spikes called fimbriae to help hold them to surfaces. Some contain little particles of minerals that orient with the planet’s magnetic fields to help the bacteria figure out whether they’re swimming up or down.

Fungi are eukaryotic organisms. This means that their DNA-containing chromosomes are enclosed within a nucleus inside their cells. (The chromosomes of bacteria and archaea are not walled off inside nuclei, making them prokaryotic organisms.)

Many decades ago, scientists thought that fungi were primitive kinds of plants. New studies looking at the DNA of fungi have confirmed that these organisms are not plants.

Unlike plants, fungi do not make their own food energy via photosynthesis, but dine on organic matter like rotting leaves, wood, and other debris, or upon the tissues of living plants and animals.

Fungi, along with bacteria, are the planet’s major composters and recyclers.

In addition to the standard HTST and UHT pasteurization standards, there are other lesser-known pasteurization techniques. The first technique, called "batch pasteurization", involves heating large batches of milk to a lower temperature, typically 155 degrees fahrenheit (or 68 C). The other technique is called higher-heat/shorter time (HHST), and it lies somewhere between HTST and UHT in terms of time and temperature.

The batch pasteurization step, which is cheap at a large scale, is often performed prior to standard pasteurization. Batch pasteurized milk is often called "raw milk" or, confusingly, "unpasteurized milk". It cannot be called "pasteurized", even though a significant number of pathogens are destroyed during the process.

In recent years, there has been some consumer interest in raw milk products, due to perceived health benefits. Advocates of raw milk maintain, correctly, that vitamins and nutrients survive much better in milk that has not been pasteurized. They also maintain that organic raw milk (most retail raw milk is also organic) is less likely to contain harmful pathogens due to better husbandry in organic dairy herds. This may be true, but it has not been proven.

However, doctors (and even most raw milk advocates) acknowledge that certain people (e.g. pregnant or breast-feeding mothers, those undergoing immunosuppression treatment for cancer, organ transplant or autoimmune diseases, and those who are immunocompromised due to diseases like AIDS) should not risk consumption of raw milk.

In fact, some doctors suggest that babies and breast-feeding mothers avoid all but UHT pasteurized dairy products.

In Africa, it is common to boil milk whenever it is harvested. This intense heating greatly changes the flavor of milk, which the people in Africa are accustomed to.

Although fungi may seem like a nuisance when they dine in your fruit bowl or refrigerator, their ability to degrade some of the toughest organic materials, including tree wood and insect exoskeletons, means that our planet is not cluttered with a mass of debris.

Fungi dine at home, eating whatever they’re growing on. Fungi secrete digestive enzymes in order to break down complex food sources, such as animal corpses and tree stumps, into smaller components they can absorb.

Algae are plant-like microorganisms that preceded plants in developing photosynthesis, the ability to turn sunlight into energy. Algae cells contain light-absorbing chloroplasts and produce oxygen through photosynthesis.

Although plants generally get the credit for producing the oxygen we breathe, some 75% or more of the oxygen in the planet’s atmosphere is actually produced by photosynthetic algae and cyanobacteria.

Algae also play an important role as the foundation for the aquatic food chain. All higher aquatic life forms depend either directly or indirectly on microscopic gardens of algae.

Most unicellular algae live in water, some dwell in moist soil, and others join with fungi to form lichens.

Green algae The most clearly plant-like algae, this species gets its namesake hue from high levels of chlorophyll.

Their cell walls are made up of cellulose, the same material that makes up the cell walls in larger, multicellular plants. Like plants, they store the food they make through photosynthesis as starches. Growing in large masses, these algae can form visible layers of slick, green scum on the surfaces and sides of ponds, puddles or damp soil.

Fossil records suggest that the first green algae originated 500 to 600 million years ago. Early algae probably gave rise to multicellular plants.

Dinoflagellates have long whip-like structures called flagella that let them turn, maneuver and spin about through the water. About 90% of these algae dwell in the ocean.

Some species glow in the dark in a process called bioluminescence. These species contain a compound called luciferin (the same compound found in fireflies). The glow increases markedly if the algae cells are agitated, as when a ship churns through the water.

About half the species of dinoflagellates are photosynthetic; the other half are predators that attack bacteria, algae, and even fish.

Dinoflagellate neurotoxins can concentrate in the bodies of shellfish and fish that eat the algal cells, in turn causing people who eat these seafoods to come down with illnesses such as paralytic shellfish poisoning and ciguatera (a combination of gastrointestinal, neurological, and cardiovascular disorders.)

So-called “red tides” occur when enormous blooms of trillions of dinoflagellates are triggered by an upwelling of nutrients from the water’s depths during warmer seasons. The population of dinoflagellates can jump to more than 20 million cells per liter of sea water along some coasts during these blooms, turning the water a reddish hue.

The name protozoa means “first animals.” As the principal hunters and grazers of the microbial world, protozoa play a key role in maintaining the balance of bacterial, algal, and other microbial life. They also are themselves an important food source for larger creatures and the basis of many food chains.

Protozoa have been found in almost every kind of soil environment from peat bogs to arid desert sands. They teem in the deep sea as well as near the surface of waters, and can be found even in frigid Arctic and Antarctic waters.

Some species of protozoa are part of the normal microbial flora of animals, and live in the guts of insects and mammals, helping to break down complex food particles into simpler molecules. A very small number of species cause disease in people, including Plasmodium vivax, which causes malaria.

Bacterial infection is the most common cause of food poisoning. In the United Kingdom during 2000 the individual bacteria involved were as follows: Campylobacter jejuni 77.3%, Salmonella 20.9%, Escherichia coli O157:H7 1.4%, and all others less than 0.1% [4] (http://www.food.gov.uk/science/sciencetopics/microbiology/58736).

Symptoms for bacterial infections are delayed because the bacteria need time to multiply. They are usually not seen until 12-36 hours after eating contaminated food.

Common bacterial foodborne pathogens are:

Aeromonas hydrophila, Aeromonas caviae, Aeromonas sobria Bacillus cereus Brucella spp. Campylobacter jejuni which causes Guillain-Barré syndrome Corynebacterium ulcerans Coxiella burnetii or Q fever Crohn's disease Escherichia coli O157:H7 enterohemorrhagic (EHEC) which causes hemolytic-uremic syndrome Escherichia coli - enteroinvasive (EIEC) Escherichia coli - enteropathogenic (EPEC) Escherichia coli - enterotoxigenic (ETEC) Listeria monocytogenes Plesiomonas shigelloides Salmonella spp. Shigella spp. Streptococcus Vibrio cholerae, including O1 and non-O1 Vibrio parahaemolyticus Vibrio vulnificus Yersinia enterocolitica and Yersinia pseudotuberculosis

The four main subgroups of protozoa are the ciliates, the flagellates, the sarcodina, and the apicomplexans.

A few ciliates can grow up to 2 millimeters in length, big enough to be seen without a microscope.

Flagellates Similarly complex single-celled organisms, flagellates have whip-like appendages called flagella sticking out of their cells.

The flagella are used for locomotion and to direct food particles or cells into the organism’s mouth-like opening. Flagellates dine on bacteria, algae, and other protozoa.

Several well-known flagellates cause parasitic diseases, such as trypanosomes that cause sleeping sickness, and Giardia lamblia, a parasite found in mountain streams and rivers that causes severe gastrointestinal distress.

Heliozoa, radiozoa, and forams tend to be passive grazers and predators, relying on suitable food swimming or drifting past to come into contact with their pseudopods.

Several species in the sarcodina group, including some species of amoebas, cover themselves with protective shell-like coverings called tests. These tests are stippled with many small and large openings through which water can flow in and out and through which the pseudopods protrude.

The tests of radiozoa are made up of silica (the same substance in diatom cell walls) and can form very intricate, lacy designs that may be studded with long spines that increase buoyancy and ward off predators.

The tests of forams are made up of sand grains or organic compounds. These can become quite large, the biggest reaching a little over 2 inches in diameter, making them some of the largest single-celled organisms known.

When forams die, their tests sink and accumulate in large batches; the Great Pyramids of Egypt are built from sandstone composed largely of fossilized giant Nummulites, an ancient kind of foram. The famous White Cliffs of Dover are limestone cliffs formed from the skeletal remains of forams.

Apicomplexans These protozoa are obligatory intracellular parasites: they must spend at least part if not all of their life cycle in a host animal.

Apicomplexans are characterized by the presence of special organelles (tiny organ-like structures) located at the tips (apices) of the cells. These organelles contain enzymes that punch through, slice open and otherwise penetrate host tissues.

The best known apicomplexan is Plasmodium, the agent that causes malaria. Plasmodium spends part of its life cycle in mosquitoes and the other part in human hosts where it ultimately infects and ruptures blood cells in large numbers.

Another familiar apicomplexan is Cryptosporidium parvum. This water-borne parasite forms extremely durable cyst-like structures that enable it to survive UV radiation and sometimes chlorine in swimming pools and treated water. An outbreak of Cryptosporidium in Milwaukee’s drinking water supply in 1993 killed 50 people and sickened more than 400,000.

Probably the best known and most deadly case of contamination in the U.S. in recent years happened in Milwaukee in 1993, when the municipal water supply was contaminated by Cryptosporidium, an intestinal protozoan. At least 50 people died, and some 400,000 people became ill, 4,000 badly enough to be hospitalized.

In 1973, a Dallas resident went out to the backyard only to stumble upon a reddish, jelly-like mass pulsating in the grass. News reports on the discovery claimed that a “new life form” had been found, and many people couldn’t help recalling the cult classic sci-fi thriller The Blob.

Scientists called to the scene, however, put any fears of menacing goo or alien creatures to rest by identifying the mass as an unusually large (46 centimeters or more than 14 inches in diameter) plasmodial slime mold.

Slime molds were once considered fungi, but unlike fungi, they can move, and their cell membranes are made of different stuff.

Slime molds are made up of individual cells that form an aggregate mass. In their visible, aggregate states, they look like blobs, gooey or foamy masses, spilled jelly, or even dog vomit. They may be bright orange, red, yellow, brown, black, blue, or white.

These large masses act like giant amoebas, creeping slowly along and engulfing food particles along the way. If a slime mold aggregate is diced up, the pieces will pull themselves back together. The blobs can navigate and avoid obstacles and if a food source is placed nearby, they seem to sense it and head unerringly for it. j, a. There are two kinds of slime molds. Plasmodial slime molds (the most common kind) share one big cell wall that surrounds thousands or millions of nuclei. Proteins called microfilaments act like tiny muscles that enable the mass to crawl at rates of about 1/25th of an inch per hour.

As long as there is enough food and moisture, the mass thrives. But when food and water are scarce, the mass separates into smaller blobs. The Plasmodium forms stalks topped by sphere-like fruiting bodies that contain spores that are carried by the rain or wind to new locations.

Cellular slime molds also produce spores, but these germinate into amoeba-like cells. The cells happily go their individual ways, as long as food and water are available.

When nutrients and moisture are scarce, individual cells send out a chemical beacon to attract other cells of the same species. The cells join up to form a mass that looks and acts like a slug to take them to a more favorable location.

Cells in cellular slime molds retain their individual cell walls when they form a mass, so the visible slug is actually a collection of hundreds of thousands of individual cells joined together.

Slime molds eat decaying vegetation, bacteria, fungi, and even other slime molds. They are most commonly found in forests.

Milk pasteurization standards have been subject to increasing scrutiny in recent years, due to the discovery of pathogens that are both widespread and heat resistant (able to survive pasteurization in significant numbers). Researchers have developed more sensitive diagnostics, such as real-time PCR and improved culture methods, that have enabled them to identify pathogens in pasteurized milk.

Note: The following paragraphs in this section discuss controversial, ongoing research.

One bacterium in particular, the organism Mycobacterium avium subspecies paratuberculosis (MAP), which causes Johne's disease in cattle and is suspected of causing at least some Crohn's disease in humans, has been found to survive pasteurization in retail milk in the U.S., the U.K., Greece, and the Czech Republic. The food safety authorities in the U.K. have decide to re-evaluate pasteurization standards in light of the MAP results and other evidence of harmful, pasteurization-resistant pathogens.

The USDA (which is responsible for setting pasteurization stardards in the U.S.) has not re-evaluated their position on pasteurization adequacy. They do not dispute the studies, which are at this point accepted by the scientific community, but maintain that the presence of MAP in retail pasteurized milk must be due to post-pasteurization contamination. However, some researchers within the FDA, which is responsible for food safety in the U.S., have begun pushing for a re-evaluation of these results. There is a small but growing body of criticism directed at these agencies by Crohn's disease sufferers, scientists, and doctors. Some have suggested that the U.S. dairy industry has been successful in suppressing the agencies' response to a potential health crisis, for fear of consumer panic which would lead to a decrease in milk consumption. It is worth noting that while MAP has not been definitely proven to be harmful in humans, all other mycobacteria are pathogenic, and it has been definitively shown to cause disease in cattle and other ruminants.

The term cold pasteurization is used sometimes for the use of radioactivity or other means (e.g. chemical) to kill bacteria in food.

Water molds are always found in wet environments, especially in fresh water sources and near the upper layers of moist soil.

Officially named Oomycota, they are also known as downy mildews and white rusts.

Water molds were long considered fungi because they produce fungi-like filamentous hyphae and feed on decaying tissue like rotting logs and mulch.

The Oomycota species Phytophthora infestans caused the Great Potato Famine that killed nearly a million people in Ireland in 1846–1847. The water mold virtually wiped out the country’s potato crops, which were an essential staple in the Irish diet (sometimes the only food on the table.)

Microbes break down food molecules our body’s enzymes and acids can’t dissolve, helping us squeeze all the nutrients out of our food. Some make valuable vitamins that our body needs. Many microbial species have proved to be consummate evolutionary wheelers and dealers, arranging collaborations, mergers, and acquisitions that usually serve both partners well. If you could peer deep into one of the many cells in your body, you’d see little blobs, squiggles, and coils. e, k. These are the cell’s organelles, structures that perform specialized functions in cells the same way that the lungs, heart, and other organs do in a body.

Mitochondria are the energy factories found in each cell of fungi, protozoa, insects, and animals. Once nutrients are absorbed or digested, they move in the form of minuscule molecules into the mitochondria, which convert the molecules into chemical energy to power the cell.

Chloroplasts undertake a similar function in the cells of plants, algae, and some protozoa. They capture sunlight and, through a series of chemical reactions called photosynthesis, use the light to make energy.

These organelles are absolutely essential to the existence of all higher life forms on Earth. If all of the mitochondria in our bodies were to suddenly shut down, we would die. The same is true for plants were they to lose their chloroplasts.

So where did they come from?

As microscopes improved over the years, scientists began noticing striking similarities in the appearances of mitochondria, chloroplasts, and bacterial cells. They discovered that these two organelles contain their own DNA, or gene set, organized very much like the DNA in bacterial cells.

Mitochondria and chloroplasts also reproduce independently from the cells in which they reside, in a manner very like bacterial fission.

Many microbiologists think it is likely that mitochondria and chloroplasts were once free-living prokaryotes (cells that lack a nucleus and organelles)