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A cluster of Escherichia coli bacteria magnified 10,000 times

A microorganism or microbe[a] is a microscopic organism, which may be single-celled or a cluster of cells.

The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from 6th century BC India, and the first century BC book On Agriculture by Marcus Terentius Varro. Microbiology, the scientific study of microorganisms, began with their observation under the microscope in the 1670s by Antonie van Leeuwenhoek. In the 19th century, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation, while Robert Koch discovered that microorganisms caused the diseases tuberculosis, cholera, and anthrax.

Microorganisms are extremely diverse, including all unicellular organisms. There are many microscopic multicellular organisms, namely micro-animals, some fungi and some algae, but these are not discussed here. Of the three domains of life identified by Carl Woese, all of the Archaea and Bacteria are microorganisms, while among the Eukarya, which contains all multicellular life forms, there are many single-celled groups formerly lumped together as "Protista", some related to animals and some to green plants.

They live in almost every habitat from the poles to the equator, deserts, geysers, rocks, and the deep sea. Some are adapted to extremes such as very hot or very cold conditions, others to high pressure and a few such as Deinococcus radiodurans to high radiation environments.

Microbes are important in human culture in many ways, serving to ferment foods, treat sewage, produce fuel, enzymes and other bioactive molecules. They are essential tools in biology as model organisms, and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. They are the pathogens responsible for many infectious diseases, and as such are the target of hygiene measures.


History of discoveryEdit

Antonie van Leeuwenhoek was the first to study microorganisms, using simple microscopes of his own design.
Lazzaro Spallanzani showed that boiling a broth stopped it from decaying.

Ancient precursorsEdit

The possible existence of microorganisms was discussed for many centuries before their discovery in the 17th century. The existence of unseen microbial life was postulated by Jainism. In the 6th century BC, Mahavira asserted the existence of unseen microbiological creatures living in earth, water, air and fire.[1] The Jain scriptures also describe nigodas, which are sub-microscopic creatures living in large clusters and having a very short life, which are said to pervade every part of the universe, even the tissues of plants and animals.[2] The earliest known idea to indicate the possibility of diseases spreading by yet unseen organisms was that of the Roman scholar Marcus Terentius Varro in a first century BC book titled On Agriculture in which he warns against locating a homestead near swamps:

… and because there are bred certain minute creatures that cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and they cause serious diseases.[3]

In The Canon of Medicine (1020), Abū Alī ibn Sīnā (Avicenna) suggested that tuberculosis and other diseases might be contagious.[4][5]

Early modernEdit

In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or even without contact over long distances.[6]

Antonie Van Leeuwenhoek (1632–1723) is considered to be the father of microbiology as he was the first to undisputedly discover, observe, describe, study and conduct scientific experiments with microoorganisms, using simple single-lensed microscopes of his own design.[7][8] Robert Hooke, a contemporary of Leeuwenhoek, also used microscopes to observe microbial life; his 1665 book Micrographia described these observations and coined the term cell.

Before Leeuwenhoek's discovery of microorganisms in 1675, it had been a mystery why grapes could be turned into wine, milk into cheese, or why food would spoil. Leeuwenhoek did not make the connection between these processes and microorganisms, but using a microscope, he did establish that there were signs of life that were not visible to the naked eye.[9][10] Leeuwenhoek's discovery, along with subsequent observations by Spallanzani and Pasteur, ended the long-held belief that life spontaneously appeared from non-living substances during the process of spoilage.[citation needed]

Lazzaro Spallanzani (1729–1799) found that boiling broth would sterilise it, killing any microorganisms in it. He also found that new microorganisms could only settle in a broth if the broth was exposed to air.

19th centuryEdit

Louis Pasteur showed that Spallanzani's findings held even if air could enter through a filter that kept particles out.
Robert Koch showed that microorganisms caused disease.

Louis Pasteur (1822–1895) expanded upon Spallanzani's findings by exposing boiled broths to the air, in vessels that contained a filter to prevent all particles from passing through to the growth medium, and also in vessels with no filter at all, with air being admitted via a curved tube that would not allow dust particles to come in contact with the broth. By boiling the broth beforehand, Pasteur ensured that no microorganisms survived within the broths at the beginning of his experiment. Nothing grew in the broths in the course of Pasteur's experiment. This meant that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory.[citation needed]

In 1876, Robert Koch (1843–1910) established that microorganisms can cause disease. He found that the blood of cattle which were infected with anthrax always had large numbers of Bacillus anthracis. Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, and this caused the healthy animal to become sick. He also found that he could grow the bacteria in a nutrient broth, then inject it into a healthy animal, and cause illness. Based on these experiments, he devised criteria for establishing a causal link between a microorganism and a disease and these are now known as Koch's postulates.[11] Although these postulates cannot be applied in all cases, they do retain historical importance to the development of scientific thought and are still being used today.[12]

Classification and structureEdit

Evolutionary tree showing all three domains of life.[13] Bacteria are in blue, Eukarya red, and Archaea green. All the groups are microorganisms except most of those in the region between Plantae and Animalia.

Microorganisms can be found almost anywhere on Earth. Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some micro-animals and plants. Viruses are generally regarded as not living and therefore not considered as microorganisms, although the field of microbiology includes virology, the study of viruses.[14][15][16]


Single-celled microorganisms were the first forms of life to develop on Earth, approximately 3–4 billion years ago.[17][18][19] Further evolution was slow,[20] and for about 3 billion years in the Precambrian eon, all organisms were microscopic.[21] So, for most of the history of life on Earth, the only forms of life were microorganisms.[22] Bacteria, algae and fungi have been identified in amber that is 220 million years old, which shows that the morphology of microorganisms has changed little since the Triassic period.[23] The newly discovered biological role played by nickel, however — especially that brought about by volcanic eruptions from the Siberian Traps — may have accelerated the evolution of methanogens towards the end of the Permian–Triassic extinction event.[24]

Microorganisms tend to have a relatively fast rate of evolution. Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation, transformation and transduction, even between widely divergent species.[25] This horizontal gene transfer, coupled with a high mutation rate and other means of transformation, allows microorganisms to swiftly evolve (via natural selection) to survive in new environments and respond to environmental stresses. This rapid evolution is important in medicine, as it has led to the development of multidrug resistant pathogenic bacteria, superbugs, that are resistant to antibiotics.[26]


Prokaryotes are organisms that lack a cell nucleus and other membrane-bound organelles. They are almost always unicellular, although some species such as myxobacteria can aggregate into complex structures as part of their life cycle.

Consisting of two domains, bacteria and archaea, the prokaryotes are the most diverse and abundant group of organisms on Earth and inhabit practically all environments where the temperature is below +140 °C. They are found in water, soil, air, as the microbiome of an organism, hot springs and even deep beneath the Earth's crust in rocks.[27] Practically all surfaces that have not been specially sterilized are covered by prokaryotes. The number of prokaryotes is estimated to be around five million trillion trillion, or 5 × 1030, accounting for at least half the biomass on Earth.[28]

The biodiversity of the prokaryotes is unknown, but may be very large. A May 2016 estimate, based on laws of scaling from known numbers of species against the size of organism, gives an estimate of perhaps 1 trillion species on the planet, of which most would be microorganisms. Currently, only one-thousandth of one percent of that total have been described.[29]


Staphylococcus aureus bacteria magnified about 10,000x

Almost all bacteria are invisible to the naked eye, with a few extremely rare exceptions, such as Thiomargarita namibiensis.[30] They lack a nucleus and other membrane-bound organelles, and can function and reproduce as individual cells, but often aggregate in multicellular colonies.[31] Their genome is usually a single loop of DNA, although they can also harbor small pieces of DNA called plasmids. These plasmids can be transferred between cells through bacterial conjugation. Bacteria are surrounded by a cell wall, which provides strength and rigidity to their cells. They reproduce by binary fission or sometimes by budding, but do not undergo meiotic sexual reproduction. However, many bacterial species can transfer DNA between individual cells by a process referred to as natural transformation.[32][33] Some species form extraordinarily resilient spores, but for bacteria this is a mechanism for survival, not reproduction. Under optimal conditions bacteria can grow extremely rapidly and can double as quickly as every 20 minutes.[34]


Archaea are also single-celled organisms that lack nuclei. In the past, the differences between bacteria and archaea were not recognised and archaea were classified with bacteria as part of the kingdom Monera. However, in 1990 the microbiologist Carl Woese proposed the three-domain system that divided living things into bacteria, archaea and eukaryotes.[35] Archaea differ from bacteria in both their genetics and biochemistry. For example, while bacterial cell membranes are made from phosphoglycerides with ester bonds, archaean membranes are made of ether lipids.[36]

Archaea were originally described in extreme environments, such as hot springs, but have since been found in all types of habitats.[37] Only now are scientists beginning to realize how common archaea are in the environment, with Crenarchaeota being the most common form of life in the ocean, dominating ecosystems below 150 m in depth.[38][39] These organisms are also common in soil and play a vital role in ammonia oxidation.[40]


Most living things that are visible to the naked eye in their adult form are eukaryotes, including humans. However, a large number of eukaryotes are also microorganisms. Unlike bacteria and archaea, eukaryotes contain organelles such as the cell nucleus, the Golgi apparatus and mitochondria in their cells. The nucleus is an organelle that houses the DNA that makes up a cell's genome. DNA (Deoxyribonuclaic acid) itself is arranged in complex chromosomes.[41] Mitochondria are organelles vital in metabolism as they are the site of the citric acid cycle and oxidative phosphorylation. They evolved from symbiotic bacteria and retain a remnant genome.[42] Like bacteria, plant cells have cell walls, and contain organelles such as chloroplasts in addition to the organelles in other eukaryotes. Chloroplasts produce energy from light by photosynthesis, and were also originally symbiotic bacteria.[42]

Unicellular eukaryotes consist of a single cell throughout their life cycle. This qualification is significant since most multicellular eukaryotes consist of a single cell called a zygote only at the beginning of their life cycles. Microbial eukaryotes can be either haploid or diploid, and some organisms have multiple cell nuclei.[43]

Unicellular eukaryotes usually reproduce asexually by mitosis under favorable conditions. However, under stressful conditions such as nutrient limitations and other conditions associated with DNA damage, they tend to reproduce sexually by meiosis and syngamy.[44]


Of eukaryotic groups, the protists are most commonly unicellular and microscopic. This is a highly diverse group of organisms that are not easy to classify.[45][46] Several algae species are multicellular protists, and slime molds have unique life cycles that involve switching between unicellular, colonial, and multicellular forms.[47] The number of species of protists is unknown since only a small proportion has been identified. Studies from 2001-2004 have shown that a high degree of protist diversity exists in oceans, deep sea-vents, river sediment and an acidic river which suggests that a large number of eukaryotic microbial communities have yet to be discovered.[48][49]

A microscopic mite Lorryia formosa


Some micro-animals are multicellular but at least one animal group, Myxozoa, is unicellular in its adult form. Microscopic arthropods include dust mites and spider mites. Microscopic crustaceans include copepods, some cladocera and water bears. Many nematodes are also too small to be seen with the naked eye. A common group of microscopic animals are the rotifers, which are filter feeders that are usually found in fresh water. Some micro-animals reproduce both sexually and asexually and may reach new habitats by producing eggs which can survive harsh environments that would kill the adult animal. However, some simple animals, such as rotifers, tardigrades and nematodes, can dry out completely and remain dormant for long periods of time.[50]


The fungi have several unicellular species, such as baker's yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe). Some fungi, such as the pathogenic yeast Candida albicans, can undergo phenotypic switching and grow as single cells in some environments, and filamentous hyphae in others.[51] Fungi reproduce both asexually, by budding or binary fission, as well by producing spores, which are called conidia when produced asexually, or basidiospores when produced sexually.[citation needed]


The green algae are a large group of photosynthetic eukaryotes that include many microscopic organisms. Although some green algae are classified as protists, others such as charophyta are classified with embryophyte plants, which are the most familiar group of land plants. Algae can grow as single cells, or in long chains of cells. The green algae include unicellular and colonial flagellates, usually but not always with two flagella per cell, as well as various colonial, coccoid, and filamentous forms. In the Charales, which are the algae most closely related to higher plants, cells differentiate into several distinct tissues within the organism. There are about 6000 species of green algae.[52]


Microorganisms are found in almost every habitat present in nature, including hostile environments such as the North and South Poles, deserts, geysers, rocks, and the deep sea. Some types of microorganisms have adapted to the extreme conditions and sustained colonies; these organisms are known as extremophiles. Extremophiles have been isolated from rocks as much as 7 kilometres below the Earth's surface,[53] and it has been suggested that the amount of organisms living below the Earth's surface is comparable with the amount of life on or above the surface.[27] Extremophiles have been known to survive for a prolonged time in a vacuum, and can be highly resistant to radiation, which may even allow them to survive in space.[54] Many types of microorganisms have intimate symbiotic relationships with other larger organisms; some of which are mutually beneficial (mutualism), while others can be damaging to the host organism (parasitism). If microorganisms can cause disease in a host they are known as pathogens and then they are sometimes referred to as microbes. Microorganisms play critical roles in Earth's biogeochemical cycles as they are responsible for decomposition and nitrogen fixation.[citation needed]


Extremophiles are microorganisms that have adapted so that they can survive and even thrive in extreme environments that are normally fatal to most life-forms.

Thermophiles and hyperthermophiles thrive in high temperatures. Psychrophiles thrive in extremely low temperatures. – Temperatures as high as 130 °C (266 °F),[55] as low as −17 °C (1 °F)[56] Halophiles thrive in high salt conditions, up to saturation.[57] Alkaliphiles thrive in an alkaline pH of about 8.5–11.[58] Acidophiles can thrive in a pH of 2.0 or less.[59]

Piezophiles thrive at very high pressures: up to 1,000-2,000 atm, down to 0 atm as in a vacuum of space.[60]

A few extremophiles such as Deinococcus radiodurans are radioresistant,[61] resisting radiation exposure of up to 5k Gy.

Extremophiles are significant in different ways. They extend terrestrial life into much of the Earth's hydrosphere, crust and atmosphere, their specific evolutionary adaptation mechanisms to their extreme environment can be exploited in biotechnology, and their very existence under such extreme conditions increases the potential for extraterrestrial life.[62]

In soilEdit

The nitrogen cycle in soils depends on the fixation of atmospheric nitrogen. This is achieved by a number of diazotrophs. One way this can occur is in the nodules in the roots of legumes that contain symbiotic bacteria of the genera Rhizobium, Mesorhizobium, Sinorhizobium, Bradyrhizobium, and Azorhizobium.[63]


A lichen is a symbiosis of a fungus with microbial algae. The algal partner is photosynthetic, enabling the fungus to live in habitats such as bare rocks where other sources of nutrition are not available.

Other fungi, including some edible mushrooms such as the cep, form mycorrhizal symbioses with trees. The fungi increase the supply of nutrients to the tree in return for a supply of energy.


Microorganisms are vital to humans and the environment, as they participate in the carbon and nitrogen cycles, as well as fulfilling other vital roles in virtually all ecosystems, such as recycling other organisms' dead remains and waste products through decomposition. Microorganisms also have an important place in most higher-order multicellular organisms as symbionts. Many blame the failure of Biosphere 2 on an improper balance of microorganisms.[64]

Food productionEdit

Microorganisms are used to make yoghurt, cheese, curd, kefir, ayran, xynogala, and other types of food. They are used to leaven bread, and to convert sugars to alcohol in wine and beer. Microorganisms are used in brewing, wine making, baking, pickling and other food-making processes.[65]

They are also used to control the fermentation process in the production of cultured dairy products such as yogurt and cheese. The cultures provide flavor and aroma, and inhibit undesirable organisms.[66]

Water treatmentEdit

The majority of all oxidative sewage treatment processes rely on a large range of microorganisms to oxidise organic constituents which are not amenable to sedimentation or flotation. Anaerobic microorganisms are also used to reduce sludge solids producing methane gas (amongst other gases) and a sterile mineralised residue. In potable water treatment, one method, the slow sand filter, employs a complex gelatinous layer composed of a wide range of microorganisms to remove both dissolved and particulate material from raw water.[67]


Microorganisms are used in fermentation to produce ethanol,[68] and in biogas reactors to produce methane.[69] Scientists are researching the use of algae to produce liquid fuels,[70] and bacteria to convert various forms of agricultural and urban waste into usable fuels.[71]

Chemicals, enzymesEdit

Microorganisms are used for many commercial and industrial production of chemicals, enzymes and other bioactive molecules.

Organic acids produced by microbial fermentation include[citation needed]

Microorganisms are used for preparation of bioactive molecules and enzymes, including:


Microorganisms are essential tools in biotechnology, biochemistry, genetics, and molecular biology. The yeasts (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe) are important model organisms in science, since they are simple eukaryotes that can be grown rapidly in large numbers and are easily manipulated.[73] They are particularly valuable in genetics, genomics and proteomics.[74][75] Microorganisms can be harnessed for uses such as creating steroids and treating skin diseases. Scientists are also considering using microorganisms for living fuel cells,[76] and as a solution for pollution.[77]


In the Middle Ages, as an early example of biological warfare, diseased corpses were thrown into castles during sieges using catapults or other siege engines. Individuals near the corpses were exposed to the pathogen and were likely to spread that pathogen to others.[78]

In modern times, bioterrorism has included the 1984 Rajneeshee bioterror attack[79] and the 1993 release of anthrax by Aum Shinrikyo in Tokyo.[80]


Microbes can make nutrients and minerals in the soil available to plants, produce hormones that spur growth, stimulate the plant immune system and trigger or dampen stress responses. In general a more diverse soil microbiome results in fewer plant diseases and higher yield.[81]

Human healthEdit

Human bacterial floraEdit

Microorganisms can form an endosymbiotic relationship with other, larger organisms. For example, microbial symbiosis plays a crucial role in the immune system. The bacteria that live within the human digestive system contribute to gut immunity, synthesize vitamins such as folic acid and biotin, and ferment complex indigestible carbohydrates.[82]


Microorganisms are the causative agents (pathogens) in many infectious diseases. The organisms involved include pathogenic bacteria, causing diseases such as plague, tuberculosis and anthrax; protozoa, causing diseases such as malaria, sleeping sickness, dysentery and toxoplasmosis; and also fungi causing diseases such as ringworm, candidiasis or histoplasmosis. However, other diseases such as influenza, yellow fever or AIDS are caused by pathogenic viruses, which are not usually classified as living organisms and are not, therefore, microorganisms by the strict definition. No clear examples of archaean pathogens are known,[83] although a relationship has been proposed between the presence of some archaean methanogens and human periodontal disease.[84]


Hygiene is a set of practices to avoid infection or food spoilage by eliminating microorganisms from the surroundings. As microorganisms, in particular bacteria, are found virtually everywhere, harmful microorganisms may be reduced to acceptable levels rather than actually eliminated. In food preparation, microorganisms are reduced by preservation methods such as cooking, cleanliness of utensils, short storage periods, or by low temperatures. If complete sterility is needed, as with surgical equipment, an autoclave is used to kill microorganisms with heat and pressure.[85][86]

See alsoEdit


  1. ^ The word microorganism (/ˌmkrˈɔːrɡənɪzəm/) uses combining forms of micro- (from the Greek: μικρός, mikros, "small") and organism from the Greek: ὀργανισμός, organismós, "organism"). It is usually styled solid but is sometimes hyphenated (micro-organism), especially in older texts. The informal synonym microbe (/ˈmkrb/) comes from μικρός, mikrós, "small" and βίος, bíos, "life".


  1. ^ Dundas, Paul; John Hinnels, eds. (2002). The Jains. London: Routledge. pp. 24, 88. ISBN 0-415-26606-8. 
  2. ^ Jaini, Padmanabh (1998). The Jaina Path of Purification. New Delhi: Motilal Banarsidass. p. 109. ISBN 81-208-1578-5. 
  3. ^ Varro On Agriculture 1, xii Loeb
  4. ^ Tschanz, David W. "Arab Roots of European Medicine". Heart Views. 4 (2). Archived from the original on 3 May 2011. 
  5. ^ Colgan, Richard (2009). Advice to the Young Physician: On the Art of Medicine. Springer. p. 33. ISBN 978-1-4419-1033-2. 
  6. ^ Nutton, Vivian (1990). "The Reception of Fracastoro's Theory of Contagion: The Seed That Fell among Thorns?". Osiris. University of Chicago Press. 2nd Series, Vol. 6, Renaissance Medical Learning: Evolution of a Tradition: 196–234. JSTOR 301787. doi:10.1086/368701. 
  7. ^ Lane, Nick (6 Mar 2015). "The Unseen World: Reflections on Leeuwenhoek (1677) 'Concerning Little Animal'". Philos Trans R Soc Lond B Biol Sci. 2015 Apr 19; 370(1666). Retrieved 16 Jan 2017. 
  8. ^ Payne, A.S. The Cleere Observer: A Biography of Antoni Van Leeuwenhoek, p. 13, Macmillan, 1970
  9. ^ Leeuwenhoek A (1753). "Part of a Letter from Mr Antony van Leeuwenhoek, concerning the Worms in Sheeps Livers, Gnats, and Animalcula in the Excrements of Frogs". Philosophical Transactions (1683–1775). 22 (260–276): 509–18. doi:10.1098/rstl.1700.0013. 
  10. ^ Leeuwenhoek A (1753). "Part of a Letter from Mr Antony van Leeuwenhoek, F. R. S. concerning Green Weeds Growing in Water, and Some Animalcula Found about Them". Philosophical Transactions (1683–1775). 23 (277–288): 1304–11. doi:10.1098/rstl.1702.0042. 
  11. ^ The Nobel Prize in Physiology or Medicine 1905 Accessed 22 November 2006.
  12. ^ O'Brien S, Goedert J (1996). "HIV causes AIDS: Koch's postulates fulfilled". Curr Opin Immunol. 8 (5): 613–18. PMID 8902385. doi:10.1016/S0952-7915(96)80075-6. 
  13. ^ Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P (2006). "Toward automatic reconstruction of a highly resolved tree of life". Science. 311 (5765): 1283–7. Bibcode:2006Sci...311.1283C. PMID 16513982. doi:10.1126/science.1123061. 
  14. ^ Lim, Daniel V (2001). eLS. John Wiley & Sons, Ltd. ISBN 9780470015902. doi:10.1038/npg.els.0000459. 
  15. ^ "What is Microbiology?". Retrieved 2017-06-02. 
  16. ^ Cann, Alan (2011). Principles of Molecular Virology (5 ed.). London: Academic Press. ISBN 978-0123849397. 
  17. ^ Schopf J (2006). "Fossil evidence of Archaean life". Philos Trans R Soc Lond B Biol Sci. 361 (1470): 869–85. PMC 1578735 . PMID 16754604. doi:10.1098/rstb.2006.1834. 
  18. ^ Altermann W, Kazmierczak J (2003). "Archean microfossils: a reappraisal of early life on Earth". Res Microbiol. 154 (9): 611–7. PMID 14596897. doi:10.1016/j.resmic.2003.08.006. 
  19. ^ Cavalier-Smith T (2006). "Cell evolution and Earth history: stasis and revolution". Philos Trans R Soc Lond B Biol Sci. 361 (1470): 969–1006. PMC 1578732 . PMID 16754610. doi:10.1098/rstb.2006.1842. 
  20. ^ Schopf J (1994). "Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic". Proc Natl Acad Sci USA. 91 (15): 6735–42. Bibcode:1994PNAS...91.6735S. PMC 44277 . PMID 8041691. doi:10.1073/pnas.91.15.6735. 
  21. ^ Stanley S (May 1973). "An Ecological Theory for the Sudden Origin of Multicellular Life in the Late Precambrian". Proc Natl Acad Sci USA. 70 (5): 1486–9. Bibcode:1973PNAS...70.1486S. PMC 433525 . PMID 16592084. doi:10.1073/pnas.70.5.1486. 
  22. ^ DeLong E, Pace N (2001). "Environmental diversity of bacteria and archaea". Syst Biol. 50 (4): 470–8. PMID 12116647. doi:10.1080/106351501750435040. 
  23. ^ Schmidt A, Ragazzi E, Coppellotti O, Roghi G (2006). "A microworld in Triassic amber". Nature. 444 (7121): 835. Bibcode:2006Natur.444..835S. PMID 17167469. doi:10.1038/444835a. 
  24. ^ Schirber, Michael (July 27, 2014). "Microbe's Innovation May Have Started Largest Extinction Event on Earth". Astrobiology Magazine. That spike in nickel allowed methanogens to take off. 
  25. ^ Wolska K (2003). "Horizontal DNA transfer between bacteria in the environment". Acta Microbiol Pol. 52 (3): 233–43. PMID 14743976. 
  26. ^ Enright M, Robinson D, Randle G, Feil E, Grundmann H, Spratt B (May 2002). "The evolutionary history of methicillin-resistant Staphylococcus aureus (MRSA)". Proc Natl Acad Sci USA. 99 (11): 7687–92. Bibcode:2002PNAS...99.7687E. PMC 124322 . PMID 12032344. doi:10.1073/pnas.122108599. 
  27. ^ a b Gold T (1992). "The deep, hot biosphere". Proc. Natl. Acad. Sci. U.S.A. 89 (13): 6045–9. Bibcode:1992PNAS...89.6045G. PMC 49434 . PMID 1631089. doi:10.1073/pnas.89.13.6045. 
  28. ^ Whitman W, Coleman D, Wiebe W (1998). "Prokaryotes: The unseen majority". Proc Natl Acad Sci USA. 95 (12): 6578–83. Bibcode:1998PNAS...95.6578W. PMC 33863 . PMID 9618454. doi:10.1073/pnas.95.12.6578. 
  29. ^ Staff (2 May 2016). "Researchers find that Earth may be home to 1 trillion species". National Science Foundation. Retrieved 6 May 2016. 
  30. ^ Schulz H, Jorgensen B (2001). "Big bacteria". Annu Rev Microbiol. 55: 105–37. PMID 11544351. doi:10.1146/annurev.micro.55.1.105. 
  31. ^ Shapiro JA (1998). "Thinking about bacterial populations as multicellular organisms" (PDF). Annu. Rev. Microbiol. 52: 81–104. PMID 9891794. doi:10.1146/annurev.micro.52.1.81. Archived from the original (PDF) on 17 July 2011. 
  32. ^ Johnsborg O, Eldholm V, Håvarstein LS (December 2007). "Natural genetic transformation: prevalence, mechanisms and function". Res. Microbiol. 158 (10): 767–78. PMID 17997281. doi:10.1016/j.resmic.2007.09.004. 
  33. ^ See also Transformation (genetics)
  34. ^ Eagon R (1962). "PSEUDOMONAS NATRIEGENS, A MARINE BACTERIUM WITH A GENERATION TIME OF LESS THAN 10 MINUTES". J Bacteriol. 83 (4): 736–7. PMC 279347 . PMID 13888946. 
  35. ^ Woese C, Kandler O, Wheelis M (1990). "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya". Proc Natl Acad Sci USA. 87 (12): 4576–9. Bibcode:1990PNAS...87.4576W. PMC 54159 . PMID 2112744. doi:10.1073/pnas.87.12.4576. 
  36. ^ De Rosa M, Gambacorta A, Gliozzi A (1 March 1986). "Structure, biosynthesis, and physicochemical properties of archaebacterial lipids". Microbiol. Rev. 50 (1): 70–80. PMC 373054 . PMID 3083222. 
  37. ^ Robertson C, Harris J, Spear J, Pace N (2005). "Phylogenetic diversity and ecology of environmental Archaea". Curr Opin Microbiol. 8 (6): 638–42. PMID 16236543. doi:10.1016/j.mib.2005.10.003. 
  38. ^ Karner MB, DeLong EF, Karl DM (2001). "Archaeal dominance in the mesopelagic zone of the Pacific Ocean". Nature. 409 (6819): 507–10. PMID 11206545. doi:10.1038/35054051. 
  39. ^ Sinninghe Damsté JS, Rijpstra WI, Hopmans EC, Prahl FG, Wakeham SG, Schouten S (June 2002). "Distribution of Membrane Lipids of Planktonic Crenarchaeota in the Arabian Sea". Appl. Environ. Microbiol. 68 (6): 2997–3002. PMC 123986 . PMID 12039760. doi:10.1128/AEM.68.6.2997-3002.2002. 
  40. ^ Leininger, S.; Urich, T.; Schloter, M.; Schwark, L.; Qi, J.; Nicol, G. W.; Prosser, J. I.; Schuster, S. C.; Schleper, C. (2006). "Archaea predominate among ammonia-oxidizing prokaryotes in soils". Nature. 442 (7104): 806–809. Bibcode:2006Natur.442..806L. PMID 16915287. doi:10.1038/nature04983. 
  41. ^ Eukaryota: More on Morphology. (Retrieved 10 October 2006)
  42. ^ a b Dyall S, Brown M, Johnson P (2004). "Ancient invasions: from endosymbionts to organelles". Science. 304 (5668): 253–7. Bibcode:2004Sci...304..253D. PMID 15073369. doi:10.1126/science.1094884. 
  43. ^ See coenocyte.
  44. ^ Bernstein, H; Bernstein, C; Michod, RE (2012). "Chapter 1". In Kimura, Sakura; Shimizu, Sora. DNA repair as the primary adaptive function of sex in bacteria and eukaryotes. DNA Repair: New Research. Hauppauge, N.Y.: Nova Sci. Publ. pp. 1–49. ISBN 978-1-62100-808-8. 
  45. ^ Cavalier-Smith T (1 December 1993). "Kingdom protozoa and its 18 phyla". Microbiol. Rev. 57 (4): 953–94. PMC 372943 . PMID 8302218. 
  46. ^ Corliss JO (1992). "Should there be a separate code of nomenclature for the protists?". BioSystems. 28 (1–3): 1–14. PMID 1292654. doi:10.1016/0303-2647(92)90003-H. 
  47. ^ Devreotes P (1989). "Dictyostelium discoideum: a model system for cell-cell interactions in development". Science. 245 (4922): 1054–8. Bibcode:1989Sci...245.1054D. PMID 2672337. doi:10.1126/science.2672337. 
  48. ^ Slapeta J, Moreira D, López-García P (2005). "The extent of protist diversity: insights from molecular ecology of freshwater eukaryotes". Proc. Biol. Sci. 272 (1576): 2073–81. PMC 1559898 . PMID 16191619. doi:10.1098/rspb.2005.3195. 
  49. ^ Moreira D, López-García P (2002). "The molecular ecology of microbial eukaryotes unveils a hidden world" (PDF). Trends Microbiol. 10 (1): 31–8. PMID 11755083. doi:10.1016/S0966-842X(01)02257-0. 
  50. ^ Lapinski J, Tunnacliffe A (2003). "Anhydrobiosis without trehalose in bdelloid rotifers". FEBS Lett. 553 (3): 387–90. PMID 14572656. doi:10.1016/S0014-5793(03)01062-7. 
  51. ^ Kumamoto CA, Vinces MD (2005). "Contributions of hyphae and hypha-co-regulated genes to Candida albicans virulence". Cell. Microbiol. 7 (11): 1546–54. PMID 16207242. doi:10.1111/j.1462-5822.2005.00616.x. 
  52. ^ Thomas, David C. (2002). Seaweeds. London: Natural History Museum. ISBN 0-565-09175-1. 
  53. ^ Szewzyk U, Szewzyk R, Stenström T (1994). "Thermophilic, anaerobic bacteria isolated from a deep borehole in granite in Sweden". Proc Natl Acad Sci USA. 91 (5): 1810–3. Bibcode:1994PNAS...91.1810S. PMC 43253 . PMID 11607462. doi:10.1073/pnas.91.5.1810. 
  54. ^ Horneck G (1981). "Survival of microorganisms in space: a review". Adv Space Res. 1 (14): 39–48. PMID 11541716. doi:10.1016/0273-1177(81)90241-6. 
  55. ^ Strain 121, a hyperthermophilic archaea, has been shown to reproduce at 121 °C (250 °F), and survive at 130 °C (266 °F).[1]
  56. ^ Some Psychrophilic bacteria can grow at −17 °C (1 °F)),[2] and can survive near absolute zero).[3]
  57. ^ Dyall-Smith, Mike, HALOARCHAEA, University of Melbourne. See also Haloarchaea.
  58. ^ Bacillus alcalophilus can grow at up to pH 11.5.[4]
  59. ^ Picrophilus can grow at pH -0.06.[5]
  60. ^ The piezophilic bacteria Halomonas salaria requires a pressure of 1,000 atm; nanobes, a speculative organism, have been reportedly found in the earth's crust at 2,000 atm.[6]
  61. ^ Anderson, A. W.; Nordan, H. C.; Cain, R. F.; Parrish, G.; Duggan, D. (1956). "Studies on a radio-resistant micrococcus. I. Isolation, morphology, cultural characteristics, and resistance to gamma radiation". Food Technol. 10 (1): 575–577. 
  62. ^ Cavicchioli, R. (2002). "Extremophiles and the search for extraterrestrial life". Astrobiology. 2 (3): 281–292. Bibcode:2002AsBio...2..281C. PMID 12530238. doi:10.1089/153110702762027862. 
  63. ^ Barea J, Pozo M, Azcón R, Azcón-Aguilar C (2005). "Microbial co-operation in the rhizosphere". J Exp Bot. 56 (417): 1761–78. PMID 15911555. doi:10.1093/jxb/eri197. 
  64. ^ Gillen, Alan L. (2007). The Genesis of Germs: The Origin of Diseases and the Coming Plagues. New Leaf Publishing Group. p. 10. ISBN 0-89051-493-3. 
  65. ^ Hui YH, Meunier-Goddik L, Josephsen J, Nip WK, Stanfield PS (2004). Handbook of Food and Beverage Fermentation Technology. CRC Press. pp. 27 and passim. ISBN 978-0-8247-5122-7. 
  66. ^ "Dairy Microbiology". University of Guelph. Retrieved 9 October 2006. 
  67. ^ Gray, N.F. (2004). Biology of Wastewater Treatment. Imperial College Press. p. 1164. ISBN 1-86094-332-2. 
  68. ^ Kitani, Osumu; Carl W. Hall (1989). Biomass Handbook. Taylor & Francis US. p. 256. ISBN 2-88124-269-3. 
  69. ^ Pimental, David (2007). Food, Energy, and Society. CRC Press. p. 289. ISBN 1-4200-4667-5. 
  70. ^ Tickell, Joshua; et al. (2000). From the Fryer to the Fuel Tank: The Complete Guide to Using Vegetable Oil as an Alternative Fuel. Biodiesel America. p. 53. ISBN 0-9707227-0-2. 
  71. ^ Inslee, Jay; et al. (2008). Apollo's Fire: Igniting America's Clean Energy Economy. Island Press. p. 157. ISBN 1-59726-175-0. 
  72. ^ Biology textbook for class XII. National council of educational research and training. p. 183. ISBN 81-7450-639-X. 
  73. ^ Castrillo JI, Oliver SG (2004). "Yeast as a touchstone in post-genomic research: strategies for integrative analysis in functional genomics". J. Biochem. Mol. Biol. 37 (1): 93–106. PMID 14761307. doi:10.5483/BMBRep.2004.37.1.093. Archived from the original on 2008-06-15. 
  74. ^ Suter B, Auerbach D, Stagljar I (2006). "Yeast-based functional genomics and proteomics technologies: the first 15 years and beyond". BioTechniques. 40 (5): 625–44. PMID 16708762. doi:10.2144/000112151. 
  75. ^ Sunnerhagen P (2002). "Prospects for functional genomics in Schizosaccharomyces pombe". Curr. Genet. 42 (2): 73–84. PMID 12478386. doi:10.1007/s00294-002-0335-6. 
  76. ^ Soni, S.K. (2007). Microbes: A Source of Energy for 21st Century. New India Publishing. ISBN 81-89422-14-6. 
  77. ^ Moses, Vivian; et al. (1999). Biotechnology: The Science and the Business. CRC Press. p. 563. ISBN 90-5702-407-1. 
  78. ^ Langford, Roland E. (2004). Introduction to Weapons of Mass Destruction: Radiological, Chemical, and Biological. Wiley-IEEE. p. 140. ISBN 0-471-46560-7. 
  79. ^ Novak, Matt (2016-11-03). "The Largest Bioterrorism Attack In US History Was An Attempt To Swing An Election". Gizmodo. 
  80. ^ CDC-Bacillus anthracis Incident, Kameido, Tokyo, 1993
  81. ^ Vrieze, Jop de (2015-08-14). "The littlest farmhands". Science. 349 (6249): 680–683. PMID 26273035. doi:10.1126/science.349.6249.680. 
  82. ^ O'Hara A, Shanahan F (2006). "The gut flora as a forgotten organ". EMBO Rep. 7 (7): 688–93. PMC 1500832 . PMID 16819463. doi:10.1038/sj.embor.7400731. 
  83. ^ Eckburg P, Lepp P, Relman D (2003). "Archaea and Their Potential Role in Human Disease". Infect Immun. 71 (2): 591–6. PMC 145348 . PMID 12540534. doi:10.1128/IAI.71.2.591-596.2003. 
  84. ^ Lepp P, Brinig M, Ouverney C, Palm K, Armitage G, Relman D (2004). "Methanogenic Archaea and human periodontal disease". Proc Natl Acad Sci USA. 101 (16): 6176–81. Bibcode:2004PNAS..101.6176L. PMC 395942 . PMID 15067114. doi:10.1073/pnas.0308766101. 
  85. ^ "Hygiene". World Health Organization (WHO). Retrieved 18 May 2017. 
  86. ^ "The Five Keys to Safer Food Programme". World Health Organization. Retrieved 18 May 2017. 

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