World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0000020377
Reproduction Date:

Title: Microorganism  
Author: World Heritage Encyclopedia
Language: English
Publisher: World Heritage Encyclopedia


A cluster of Escherichia coli bacteria magnified 10,000 times

A microorganism (from the Antonie van Leeuwenhoek, using a microscope of his own design.

Microorganisms are very diverse and include all the

  • Our Microbial Planet A free poster from the National Academy of Sciences about the positive roles of micro-organisms.
  • "Uncharted Microbial World: Microbes and Their Activities in the Environment" Report from the American Academy of Microbiology
  • Understanding Our Microbial Planet: The New Science of Metagenomics A 20-page educational booklet providing a basic overview of metagenomics and our microbial planet.
  • Tree of Life Eukaryotes
  • Microbe News from Genome News Network
  • Medical Microbiology On-line textbook
  • Through the microscope: A look at all things small On-line microbiology textbook by Timothy Paustian and Gary Roberts, University of Wisconsin-Madison
  • Microorganisms in the pond water on YouTube
  • Methane-spewing microbe blamed in worst mass extinction. CBCNews

External links

  1. ^ Madigan M, Martinko J (editors) (2006). Brock Biology of Microorganisms (13th ed.). Pearson Education. p. 1096.  
  2. ^ Rybicki EP (1990). "The classification of organisms at the edge of life, or problems with virus systematics". S Aft J Sci 86: 182–6.  
  3. ^ LWOFF A (1956). "The concept of virus". J. Gen. Microbiol. 17 (2): 239–53.  
  4. ^ a b University of Georgia (25 August 1998). "First-Ever Scientific Estimate Of Total Bacteria On Earth Shows Far Greater Numbers Than Ever Known Before".  
  5. ^ Zhang, K. Dose; A. Bieger-Dose, R. Dillmann, M. Gill, O. Kerz, A. Klein, H. Meinert, T. Nawroth, S. Risi, C. Stride (1995). "ERA-experiment "space biochemistry"". Advances in Space Research 16 (8): 119–129.  
  6. ^ Vaisberg, Horneck G; Eschweiler U, Reitz G, Wehner J, Willimek R, Strauch K. (1995). "Biological responses to space: results of the experiment "Exobiological Unit" of ERA on EURECA I". Adv Space Res. 16 (8): 105–18.  
  7. ^ Staff (2014). "The Biosphere".  
  8. ^ a b c Choi, Charles Q. (17 March 2013). "Microbes Thrive in Deepest Spot on Earth".  
  9. ^ Glud, Ronnie; Wenzhöfer, Frank; Middelboe, Mathias; Oguri, Kazumasa; Turnewitsch, Robert; Canfield, Donald E.; Kitazato, Hiroshi (17 March 2013). "High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth".  
  10. ^ Oskin, Becky (14 March 2013). "Intraterrestrials: Life Thrives in Ocean Floor".  
  11. ^ Fox, Douglas (20 August 2014). "Lakes under the ice: Antarctica’s secret garden".  
  12. ^ Mack, Eric (20 August 2014). "Life Confirmed Under Antarctic Ice; Is Space Next?".  
  13. ^ Christner BC, Morris CE, Foreman CM, Cai R, Sands DC (2008). "Ubiquity of biological ice nucleators in snowfall". Science 319 (5867): 1214.  
  14. ^ 2002 WHO mortality data Accessed 20 January 2007
  15. ^ Schopf J (2006). "Fossil evidence of Archaean life". Philos Trans R Soc Lond B Biol Sci 361 (1470): 869–85.  
  16. ^ Altermann W, Kazmierczak J (2003). "Archean microfossils: a reappraisal of early life on Earth". Res Microbiol 154 (9): 611–7.  
  17. ^ Cavalier-Smith T (2006). "Cell evolution and Earth history: stasis and revolution". Philos Trans R Soc Lond B Biol Sci 361 (1470): 969–1006.  
  18. ^ 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.  
  19. ^ 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.  
  20. ^ DeLong E, Pace N (2001). "Environmental diversity of bacteria and archaea". Syst Biol 50 (4): 470–8.  
  21. ^ Schmidt A, Ragazzi E, Coppellotti O, Roghi G (2006). "A microworld in Triassic amber". Nature 444 (7121): 835.  
  22. ^ 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. 
  23. ^ Wolska K (2003). "Horizontal DNA transfer between bacteria in the environment". Acta Microbiol Pol 52 (3): 233–43.  
  24. ^ 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.  
  25. ^ Mahavira is dated 599 BCE - 527 BCE. See. Dundas, Paul; John Hinnels ed. (2002). The Jains. London: Routledge.   p. 24
  26. ^ Dundas, Paul (2002) p. 88
  27. ^ Jaini, Padmanabh (1998). The Jaina Path of Purification. New Delhi: Motilal Banarsidass.   p. 109
  28. ^ Varro On Agriculture 1,xii Loeb
  29. ^ Tschanz, David W. "Arab Roots of European Medicine". Heart Views 4 (2). 
  30. ^ Colgan, Richard (2009). Advice to the Young Physician: On the Art of Medicine. Springer. p. 33.  
  31. ^ Payne, A.S. The Cleere Observer: A Biography of Antoni Van Leeuwenhoek, p. 13, Macmillan, 1970
  32. ^ 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.  
  33. ^ 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.  
  34. ^ The Nobel Prize in Physiology or Medicine 1905 Accessed 22 November 2006.
  35. ^ O'Brien S, Goedert J (1996). "HIV causes AIDS: Koch's postulates fulfilled". Curr Opin Immunol 8 (5): 613–18.  
  36. ^ Borenstein, Seth (13 November 2013). "Oldest fossil found: Meet your microbial mom".  
  37. ^ Noffke, Nora; Christian, Christian; Wacey, David; Hazen, Robert M. (8 November 2013). "Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia".  
  38. ^ 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.  
  39. ^ a b Gold T (1992). "The deep, hot biosphere". Proc. Natl. Acad. Sci. U.S.A. 89 (13): 6045–9.  
  40. ^ Whitman W, Coleman D, Wiebe W (1998). "Prokaryotes: The unseen majority". Proc Natl Acad Sci USA 95 (12): 6578–83.  
  41. ^ Schulz H, Jorgensen B (2001). "Big bacteria". Annu Rev Microbiol 55: 105–37.  
  42. ^  
  43. ^ Johnsborg O, Eldholm V, Håvarstein LS (December 2007). "Natural genetic transformation: prevalence, mechanisms and function". Res. Microbiol. 158 (10): 767–78.  
  44. ^ See also Transformation (genetics)
  45. ^ a b Bernstein H, Bernstein C, Michod RE (2012). DNA repair as the primary adaptive function of sex in bacteria and eukaryotes. Chapter 1: pp.1-49 in: DNA Repair: New Research, Sakura Kimura and Sora Shimizu editors. Nova Sci. Publ., Hauppauge, N.Y. ISBN 978-1-62100-808-8
  46. ^ See also Natural competence
  48. ^ 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.  
  49. ^ De Rosa M, Gambacorta A, Gliozzi A (1 March 1986). "Structure, biosynthesis, and physicochemical properties of archaebacterial lipids". Microbiol. Rev. 50 (1): 70–80.  
  50. ^ Robertson C, Harris J, Spear J, Pace N (2005). "Phylogenetic diversity and ecology of environmental Archaea". Curr Opin Microbiol 8 (6): 638–42.  
  51. ^
  52. ^ 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.  
  53. ^ Leininger S, Urich T, Schloter M, et al. (2006). "Archaea predominate among ammonia-oxidizing prokaryotes in soils". Nature 442 (7104): 806–9.  
  54. ^ Eukaryota: More on Morphology. (Retrieved 10 October 2006)
  55. ^ a b Dyall S, Brown M, Johnson P (2004). "Ancient invasions: from endosymbionts to organelles". Science 304 (5668): 253–7.  
  56. ^ See coenocyte.
  57. ^ Also see Meiosis.
  58. ^ Cavalier-Smith T (1 December 1993). "Kingdom protozoa and its 18 phyla". Microbiol. Rev. 57 (4): 953–94.  
  59. ^ 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. 
  60. ^ Devreotes P (1989). "Dictyostelium discoideum: a model system for cell-cell interactions in development". Science 245 (4922): 1054–8.  
  61. ^ 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.  
  62. ^ Moreira D, López-García P (2002). "The molecular ecology of microbial eukaryotes unveils a hidden world". Trends Microbiol. 10 (1): 31–8.  
  63. ^ Lapinski J, Tunnacliffe A (2003). "Anhydrobiosis without trehalose in bdelloid rotifers". FEBS Lett. 553 (3): 387–90.  
  64. ^ Kumamoto CA, Vinces MD (2005). "Contributions of hyphae and hypha-co-regulated genes to Candida albicans virulence". Cell. Microbiol. 7 (11): 1546–54.  
  65. ^
  66. ^ 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.  
  67. ^ Horneck G (1981). "Survival of microorganisms in space: a review". Adv Space Res 1 (14): 39–48.  
  68. ^ Strain 121, a hyperthermophilic archaea, has been shown to reproduce at 121 °C (250 °F), and survive at 130 °C (266 °F).[1]
  69. ^ Some Psychrophilic bacteria can grow at −17 °C (1 °F),[2] and can survive near absolute zero.[3]
  70. ^ Picrophilus can grow at pH -0.06.[4]
  71. ^ The alkaliphilic bacteria Bacillus alcalophilus can grow at up to pH 11.5.[5]
  72. ^ Dyall-Smith, Mike, HALOARCHAEA, University of Melbourne. See also Haloarchaea.
  73. ^ The See Deinococcus radiodurans ^
  74. ^ Cavicchioli R (2002). "Extremophiles and the search for extraterrestrial life". Astrobiology 2 (3): 281–92.  
  75. ^ Barea J, Pozo M, Azcón R, Azcón-Aguilar C (2005). "Microbial co-operation in the rhizosphere". J Exp Bot 56 (417): 1761–78.  
  76. ^ Gillen, Alan L. (2007). The Genesis of Germs: The Origin of Diseases and the Coming Plagues. New Leaf Publishing Group. p. 10.  
  77. ^ "Dairy Microbiology". University of Guelph. Retrieved 9 October 2006. 
  78. ^ Gray, N.F. (2004). Biology of Wastewater Treatment. Imperial College Press. p. 1164.  
  79. ^ Kitani, Osumu and Carl W. Hall (1989). Biomass Handbook. Taylor & Francis US. p. 256.  
  80. ^ Pimental, David (2007). Food, Energy, and Society. CRC Press. p. 289.  
  81. ^ 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.  
  82. ^ Inslee, Jay et al. (2008). Apollo's Fire: Igniting America's Clean Energy Economy. Island Press. p. 157.  
  83. ^ Biology textbook for class XII. National council of educational research and training. p. 183.  
  84. ^ 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.  
  85. ^ 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.  
  86. ^ Sunnerhagen P (2002). "Prospects for functional genomics in Schizosaccharomyces pombe". Curr. Genet. 42 (2): 73–84.  
  87. ^ Soni, S.K. (2007). Microbes: A Source of Energy for 21st Century. New India Publishing.  
  88. ^ Moses, Vivian et al. (1999). Biotechnology: The Science and the Business. CRC Press. p. 563.  
  89. ^ Langford, Roland E. (2004). Introduction to Weapons of Mass Destruction: Radiological, Chemical, and Biological. Wiley-IEEE. p. 140.  
  90. ^ O'Hara A, Shanahan F (2006). "The gut flora as a forgotten organ". EMBO Rep 7 (7): 688–93.  
  91. ^ Eckburg P, Lepp P, Relman D (2003). "Archaea and Their Potential Role in Human Disease". Infect Immun 71 (2): 591–6.  
  92. ^ 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.  


See also

There are no conditions where all microorganisms would grow, and therefore often several methods are needed. For example, a food sample might be analyzed on three different nutrient mediums designed to indicate the presence of "total" bacteria (conditions where many, but not all, bacteria grow), molds (conditions where the growth of bacteria is prevented by, e.g., antibiotics) and coliform bacteria (these indicate a sewage contamination).

There are several methods for investigating the level of hygiene in a sample of food, drinking water, equipment, etc. Water samples can be filtrated through an extremely fine filter. This filter is then placed in a selective media or polymerase chain reaction, can then be used for detection. The hygiene of hard surfaces, such as cooking pots, can be tested by touching them with a solid piece of nutrient medium and then allowing the microorganisms to grow on it.

In food preparation microorganisms are reduced by preservation methods (such as the addition of vinegar), clean utensils used in preparation, short storage periods, or by cool temperatures. If complete sterility is needed, the two most common methods are irradiation and the use of an autoclave, which resembles a pressure cooker.

Hygiene is the avoidance of viruses. A good example of this is a hypodermic needle.


Microorganisms are critical to the processes of decomposition required to cycle nitrogen and other elements in the natural environment.

Importance in ecology

[93].periodontal disease although a relationship has been proposed between the presence of some archaean methanogens and human [92] Microorganisms are the cause of many infectious diseases. The organisms involved include

Diseases caused by microbes

Microorganisms can form an vitamins such as folic acid and biotin, and ferment complex indigestible carbohydrates.[91]

Human digestion

Importance in human health

In the Middle Ages, 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.[90]

Use in warfare

Microorganisms are essential tools in fuel cells,[88] and as a solution for pollution.[89]

Use in science

Microorganisms are used for preparation of bioactive molecules and enzymes.

Microorganisms are used for many commercial and industrial production of chemicals, enzymes and other bioactive molecules.
Examples of organic acid produced include

Use in production of chemicals, enzymes etc.

Microorganisms are used in fermentation to produce ethanol,[80] and in biogas reactors to produce methane.[81] Scientists are researching the use of algae to produce liquid fuels,[82] and bacteria to convert various forms of agricultural and urban waste into usable fuels.[83]

Use in energy

[79] 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

Use in water treatment

[78] They are also used to control the

Microorganisms are used in brewing, wine making, baking, pickling and other food-making processes.

Use in food production

The morphology of the intestine of germ-free animals differs considerably from normal animals - villi of the small intestine are remarkably regular, the rate of epithelial cell renew is reduced and, as one would expect, the number and size of Peyer's patches is reduced. The cecum of germ-free rats is roughly 10 times the size of that in a conventional rat. Bacteria in the intestinal lumen metabolize a variety of sterols and steroids. For example, bacteria convert the bile salt cholic acid to deoxycholic acid. Small intestinal bacteria also have an important role in sex steroid metabolism. Finally, bacterial populations in the large intestine digest carbohydrates, proteins and lipids that escape digestion and absorption in small intestine. This fermentation, particularly of cellulose, is of critical importance to herbivores like cattle and horses which make a living by consuming plants. However, it seems that even species like humans and rodents derive significant benefit from the nutrients liberated by intestinal microorganisms.

It is also clear that microbial populations exert a profound effect on structure and function of the digestive tract. For example:

The gastrointestinal tract is sterile at birth, but colonization typically begins within a few hours of birth, starting in the small intestine and progressing caudally over a period of several days. In most circumstances, a "mature" microbial flora is established by 3 to 4 weeks of age.

In sharp contrast to the stomach and small intestine, the contents of the colon literally teem with bacteria, predominantly strict anaerobes (bacteria that survive only in environments virtually devoid of oxygen). Between these two extremes is a transitional zone, usually in the ileum, where moderate numbers of both aerobic and anaerobic bacteria are found.

The number and type of bacteria in the gastrointestinal tract vary dramatically by region. In healthy individuals the stomach and proximal small intestine contain few microorganisms, largely a result of the bacteriocidal activity of gastric acid; those that are present are aerobes and facultative anaerobes. One interesting testimony to the ability of gastric acid to suppress bacterial populations is seen in patients with achlorhydria, a genetic condition which prevents secretion of gastric acid. Such patients, which are otherwise healthy, may have as many as 10,000 to 100,000,000 microorganisms per ml of stomach contents.

The gastrointestinal tract contains an immensely complex ecology of microorganisms. A typical person harbors more than 500 distinct species of bacteria, representing dozens of different lifestyles and capabilities. The composition and distribution of this menagerie varies with age, state of health and diet.

Some forms of bacteria that live in animals' stomachs help in their digestion. For example, cows have a variety of different microorganisms in their stomachs that are essential in their digestion of grass and hay.

Use in digestion

[77] Microorganisms are vital to humans and the environment, as they participate in the


lichen. Certain fungi form mycorrhizal symbioses with trees that increase the supply of nutrients to the tree.

Symbiotic microorganisms

The nitrogen cycle in soils depends on the fixation of atmospheric nitrogen. 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.[76]

Soil microorganisms

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 bio-technology, and their very existence under such extreme conditions increases the potential for extraterrestrial life.[75]

Extremophiles are microorganisms that have adapted so that they can survive and even thrive in conditions that are normally fatal to most life-forms. For example, some species have been found in the following extreme environments:


Microorganisms are found in almost every disease in a host they are known as pathogens and then they are sometimes referred to as microbes.

Habitats and ecology

[65] The


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.[64] 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.


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.[63]


A microscopic mite Lorryia formosa.

[62][61] The number of species of protists is unknown since we may have identified only a small portion. 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.[60] have unique life cycles that involve switching between unicellular, colonial, and multicellular forms.slime molds protists, and multicellular are species algae Several [59][58] Of


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.[45][57]

Unicellular eukaryotes consist of a single cell nuclei.[56]

Most living things that are visible to the naked eye in their adult form are light by photosynthesis, and were also originally symbiotic bacteria.[55]


Archaea were originally described in extreme environments, such as ammonia oxidation.[53]

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.[48] 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.[49]


[47], 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.spores Some species form extraordinarily resilient [46][45] In nature, the development of competence for transformation is usually associated with stressful environmental conditions, and seems to be an adaptation for facilitating repair of DNA damage in recipient cells.[44][43]. However, many bacterial species can transfer DNA between individual cells by a process referred to as natural transformation.sexual reproduction meiotic, but do not undergo budding or sometimes by binary fission, which provides strength and rigidity to their cells. They reproduce by cell wall. Bacteria are surrounded by a bacterial conjugation. These plasmids can be transferred between cells through plasmids, although they can also harbor small pieces of DNA called DNA Their genome is usually a single loop of [42] Almost all bacteria are invisible to the naked eye, with a few extremely rare exceptions, such as

Staphylococcus aureus bacteria magnified about 10,000x


Consisting of two Earth and inhabit practically all environments where the temperature is below +140 °C. They are found in water, soil, air, animals' gastrointestinal tracts, hot springs and even deep beneath the Earth's crust in rocks.[39] Practically all surfaces that have not been specially sterilized are covered by prokaryotes. The number of prokaryotes on Earth is estimated to be around five million trillion trillion, or 5 × 1030, accounting for at least half the biomass on Earth.[40]

Prokaryotes are organisms that lack a myxobacteria can aggregate into complex structures as part of their life cycle.


Microorganisms can be found almost anywhere in the microbiology also encompasses the study of viruses.

Evolutionary tree showing the common ancestry of all three domains of life.[38] Bacteria are colored blue, eukaryotes red, and archaea green. Relative positions of some phyla are shown around the tree.

Classification and structure

On 8 November 2013, scientists reported the discovery of what may be the earliest signs of life on Earth—the oldest complete fossils of a microbial mat (associated with sandstone in Western Australia) estimated to be 3.48 billion years old.[36][37]

In 1876, Koch's postulates.[34] 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.[35]

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.

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.

from non-living substances during the process of spoilage. spontaneously appeared Leeuwenhoek's discovery, along with subsequent observations by Spallanzani and Pasteur, ended the long-held belief that life [33][32] Before Leeuwenhoek's discovery of microorganisms in 1675, it had been a mystery why

. cell describes these observations and coined the term Micrographia, a contemporary of Leeuwenhoek, also used microscopes to observe microbial life; his 1665 book Robert Hooke [31]

Louis Pasteur showed that Spallanzani's findings held even if air could enter through a filter that kept particles out
Lazzaro Spallanzani showed that boiling a broth stopped it from decaying

History of microorganisms' discovery

All these early claims about the existence of microorganisms were speculative and were not based on any data or science. Microorganisms were neither proven, observed, nor correctly and accurately described until the 17th century. The reason for this was that all these early studies lacked the microscope.

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.

In The Canon of Medicine (1020), Abū Alī ibn Sīnā (Avicenna) hypothesized that tuberculosis and other diseases might be contagious[29][30]

… 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.[28]

The possibility that microorganisms exist was discussed for many centuries before their discovery in the 17th century. The existence of unseen microbiological life was postulated by Roman scholar Marcus Terentius Varro in a 1st-century BC book titled On Agriculture in which he warns against locating a homestead near swamps:


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 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 recent development of "super-bugs", pathogenic bacteria that are resistant to modern antibiotics.[24]

Single-celled microorganisms were the Triassic period.[21] The newly discovered biological role played by nickel, however — especially that engendered by volcanic eruptions from the Siberian Traps (site of the modern city of Norilsk) — is thought to have accelerated the evolution of methanogens towards the end of the Permian–Triassic extinction event.[22]



  • Evolution 1
  • Pre-microbiology 2
  • History of microorganisms' discovery 3
  • Classification and structure 4
    • Prokaryotes 4.1
      • Bacteria 4.1.1
      • Archaea 4.1.2
    • Eukaryotes 4.2
      • Protists 4.2.1
      • Animals 4.2.2
      • Fungi 4.2.3
      • Plants 4.2.4
  • Habitats and ecology 5
    • Extremophiles 5.1
    • Soil microorganisms 5.2
    • Symbiotic microorganisms 5.3
  • Importance 6
    • Use in digestion 6.1
    • Use in food production 6.2
    • Use in water treatment 6.3
    • Use in energy 6.4
    • Use in production of chemicals, enzymes etc. 6.5
    • Use in science 6.6
    • Use in warfare 6.7
  • Importance in human health 7
    • Human digestion 7.1
    • Diseases caused by microbes 7.2
  • Importance in ecology 8
  • Hygiene 9
  • See also 10
  • References 11
  • External links 12

Microorganisms are crucial to nutrient recycling in pathogenic and cause disease and even death in plants and animals.[14] Microorganisms are often referred to as microbes, but this is usually used in reference to pathogens.

Microorganisms live in every part of the Antarctica.[11][12] According to one researcher,"You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are."[8]


This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.