from Wikipedia, the free encyclopedia

A microorganism or a microbe is a microscopically small creatures (organism), which does not as an individual with the naked eye can be seen, therefore, in at least two dimensions less than about 30 microns (0.03 mm). Most microorganisms are single-celled organisms , but they also include small-cell organisms ( fungi , algae ) of the appropriate size. Such tiny living beings, which are contrasted (separated from) the rest of the animal and plant kingdom only because of their small size , are the subject of microbiology . But they do not form a uniform group in the system of living beings .

The microorganisms include bacteria (eg. As lactic acid bacteria ), many fungi (eg. As baker's yeast ), microscopic algae (z. B. chlorella ) and protozoa (eg. As paramecium and malaria germs can Plasmodium ). It is controversial whether viruses should also be counted among the microorganisms. For the most part, they are not viewed as living beings and therefore not as microorganisms. Nevertheless, virus research ( virology ) is regarded as a branch of microbiology.

Microorganisms are generally materials cycle important one hand, they form a producer (eg. Micro-algae , cyanobacteria ), the basis of many food chains , on the other hand build a decomposer ( decomposers ) organic matter to inorganic substances from. Some microorganisms are of particular importance to humans: for nutrition , for the desired metabolism (e.g. antibiotic producers ), as parasites and as pathogens for infectious diseases .

Microorganisms far outnumber all other living beings in terms of number and mass, with 70 percent they represent the largest proportion of living matter ( biomass ).

Other names

Microorganisms are also known as microbes (formerly also microbes ) or micro-organisms (including microorganisms hereinafter). The word microbe as a general term for small organisms (such as vibrios , bacteria, "bacteridia", "monads", "mycoderms" and infusoria ) was coined in 1878 by the French doctor Charles Emmanuel Sédillot.

Groups of microorganisms


The bacteria (Bacteria) ( ancient Greek βακτηρἱα bakteria , German , Pole ' ) form in addition to the eukaryotes and archaea one of three fundamental domains , all now in the living things are divided.

Individuals of the bacterial species Escherichia coli . Secondary electron micrograph. The diameter of a bacterium is 0.6 µm.

Traditionally, the term “bacteria” is sometimes still used in microbiology today for almost all microscopic, mostly unicellular organisms that do not have a real cell nucleus and therefore belong to the prokaryotes . However, this also includes the archaea . It is correct to assign the archaea and the bacteria to a separate domain (archaea, bacteria). To differentiate the bacteria from the archaea one sometimes speaks of "real bacteria" or "real bacteria". In the past, they were also called Eubacteria with a scientific name to distinguish them from the Archaea, then called Archaebacteria. This was an unfortunate name because there is also a bacterial genus Eubacterium .

Bacteria are prokaryotes , which means that their DNA is not contained in a cell nucleus that is separated from the cytoplasm by a double membrane , as in eukaryotes, but with them, as in all prokaryotes, the DNA lies freely in the cytoplasm, compressed into a narrow space, also nucleoid ( nuclear equivalent ) called.

Bacteria were first observed in water and in human saliva by Antoni van Leeuwenhoek using self-made microscopes and described by him in reports to the Royal Society of London in 1676 .

More than three hundred years after the description of the first bacteria and despite countless already described and cataloged species, it can be assumed, based on current knowledge, that the vast majority of 95 to 99% of all bacterial species existing on our planet are not yet known and have not been described (status: 2006 ). It is therefore not surprising that new and exciting discoveries are made again and again. In 1999, the largest known bacterium was discovered: the so-called sulfur pearl of Namibia, Thiomargarita namibiensis , is a bacterium that is visible to the naked eye with a diameter of up to three quarters of a millimeter.

The scientific discipline that deals with the study of bacteria is bacteriology .


The archaea form one of the three domains of living things. In the past, they were counted among the bacteria and called archaebacteria, but differ from them in several ways (e.g. stability of membrane and cell wall structures, components of the transcription and translation systems ).

The archaea include:

  • extremely halophilic archaea. They live in environments with a very high concentration of salt.
  • hyperthermophilic archaea. With a temperature optimum> 80 ° C, they have a pronounced heat stability. They can still grow at the boiling point of water, but not below 60 ° C. They occur, for example, in hydrothermal springs and in hot water chimneys in the deep sea.
  • methanogenic archaea. These strictly anaerobic organisms produce methane . You come z. B. in swamps , in cattle rumen and in rice fields , but also in the digesters of sewage treatment plants . As methane producers, they are jointly responsible for the greenhouse effect .


Fungi (Fungi) are eukaryotes and, like baker's yeast, occur as single-celled cells or, like mycelial fungi, as multicellular cells. Their reproduction and spread occurs sexually and asexually through spores or vegetatively through the spread (possibly with fragmentation) of the mycelia, which in various cases are very long-lived. Fungi are heterotrophic and mostly feed by excreting enzymes in the immediate vicinity and thus breaking down polymeric , water-insoluble nutrients and absorbing them into the cells.

Fungi differ from plants in their heterotrophic way of life without photosynthesis , and most also in the presence of chitin in the cell wall . They differ from animals, among other things, in the presence of a cell wall.

The groups formerly referred to as “lower fungi”, ie slime molds , fungi-like protists such as egg fungi (Oomycota) or Hypochytriomycota are no longer counted among the fungi (Fungi).

The scientific discipline that deals with the study of fungi is mycology .


The term alga in a broader sense includes eukaryotic organisms that live in the water and carry out photosynthesis , but do not belong to plants . In the narrower sense, it refers to numerous groups of protists . Algae include both microscopic, single-celled and multicellular, sometimes huge, plant-like creatures. By definition, only one- to few-cell algae are regarded as microorganisms; they are referred to as microalgae . Like all algae, microalgae perform photosynthesis, use light as an energy source and are carbon autotrophic . Algae do not represent a real family group in the sense of phylogeny and systematics , but are a paraphyletic group. Nevertheless, the term is also often used as a general term in biology.

The scientific discipline that deals with the study of algae is phycology.


Thecamoeba . Thecamoeben are among the frequent residents of forest floors
Colpoda inflata is a protozoon that occurs in many soils

Protozoa (singular protozoon ), also primal animals, is a name for single-cell organisms that were formerly regarded as animal due to their heterotrophic way of life and their mobility . They do not have a cell wall but, unlike bacteria, have a nucleus , i.e. are eukaryotes . The term was introduced to science by the German Georg August Goldfuß in 1818. First, the protozoa were placed together with other eukaryotic (nucleated) unicellular organisms in their own realm, namely the realm of the protista . Today we know, however, that the terms “protozoa” and “protista” are just as little systematic taxa as the terms “ algae ”, “ amoeba ”, “ ciliates ” or “ flagellates ”, as this classification is mainly based on visible features, such named habitus was taken, but not due to natural relationship. Of the approximately 40,000 "protozoan species" described, around 8,000 are parasites , of which around 70 parasitize humans . Only about 40 infections by protozoa can also cause disease .

Some parasitic protozoa actually do not belong to the protozoa, but to the algae, because they contain a leukoplast, e.g. B. the Apicomplexa , to which Plasmodium , the causative agent of malaria , belongs or Helicosporidium , a colorless green alga that parasitizes in invertebrates ( invertebrates ).

The scientific discipline that deals with the study of protozoa is protozoology.


Since viruses do not have an independent metabolism and cannot reproduce on their own, most biologists do not regard them as living beings, but rather as organic structures that interact with living beings, or as "borderline cases of life". The affiliation to the microorganisms is therefore controversial. However, microbiologists also research viruses, and virology is considered a branch of microbiology.

Importance of microorganisms

Evolution, genetics, number of species

Microorganisms appeared as the first organisms on earth about 3.8 billion years ago, multicellular cells only developed about 600 million years ago in the Neoproterozoic and the first "modern" humans ( Homo sapiens ) only appeared about 130,000 years ago.

The genomes of microorganisms usually consist of no more than 10 million DNA bases and are therefore not very complex compared to the approximately 3 billion bases in the genome of humans or mice . The simple construction plan enables the microorganisms, among other things, to reproduce quickly - the intestinal bacterium Escherichia coli doubles every 20 minutes under optimal conditions. It is also the prerequisite for the adaptability of the microorganisms to different environmental conditions or host organisms and for the great diversity of species.

The number of species can only be estimated; it could be several billion. Only a very small proportion of these species have been discovered and classified so far . More than 20,000 different types of microorganisms can live in one liter of seawater, and up to ten million species in the oceans .


Microorganisms drive the geochemical conversions that are important for life on our planet and also influence the global climate . The microbial metabolism of critical chemical elements such as carbon or nitrogen helps to keep the earth habitable for all other living things. Microorganisms produce at least half of the planet's elemental oxygen (O 2 ).

Microorganisms thrive in an astonishing variety of very different habitats : in acidic as well as in alkaline or salty environments , at extremely high or low temperatures ( extremophiles ), under high pressure , in the dark or with strong radiation . They often live where no other living beings can exist and get their nutrients exclusively from inorganic material. Some microorganisms are even able to settle in biotopes that are massively contaminated with numerous poisons such as heavy metals , nitrates and radionuclides such as uranium and technetium . The extremophilic bacterium Deinococcus radiodurans was found in the cooling water circuit of nuclear power plants and in arsenic-contaminated waste.

The composition of the biocenosis with regard to its species ( English diversity pattern ) in a biotope and its changes can be used to monitor the biotope or to predict changes in an ecosystem .

Beneficial microorganisms

Many microorganisms are believed to be useful for a variety of reasons. Many play a role in the geochemical material cycles (examples: nitrogen cycle , N 2 fixation , wastewater treatment ). In the food industry , microorganisms are used to produce certain foods . In biotechnology , they serve as producers of pharmaceuticals (e.g. antibiotics and insulin ) or technically usable substances. Microorganisms are also used in pest control as an alternative to toxic chemical agents.

In the future, biotechnological use could play an even greater role in various areas, such as energy generation or the biological degradation of waste and pollutants . A well-known example is oil spills on the sea: If crude oil or petroleum products leak from tankers in the event of an accident, special microbes "eat" the pollutants floating in the sea as a "carpet".

Microorganisms in the human body

The number of microorganisms (mainly bacteria ) that exist on and in the human body is about 10 to 100 times higher than the number of cells that make up a human being: About 1 quadrillion (10 15 ) microorganisms are 10– 100 trillion (10 13 -10 14 ) human cells. This corresponds to a total mass of 0.5 to 1 kg of microorganisms. The individual history of settlement already begins during birth. Gradually, this microflora is individually transformed under the influence of the environment and genes.

Numerous strains of microorganisms live, for example, on the skin , in the mouth , in the nose and in the intestines . The trunks in the crook of the arm differ considerably from those on the forearm skin. However, healthy people in the same region have almost the same population of microorganisms.

  • On one square centimeter of skin - assuming bacteria 1 µm long and 0.5 µm wide - there is theoretically room for 200 million bacteria. In fact, only about 100 to 10,000 bacteria live per cm² of skin area; the skin is therefore relatively low in germs.
  • In the gastrointestinal tract they form the intestinal flora and produce vitamins (biotin, folic acid and vitamin K), strengthen the immune system and prevent the settlement and spread of pathogenic bacteria and fungi. Human feces contain around 100 billion microorganisms per gram. The lining of the intestine prevents the bacteria from entering the body. Soon after death , the body is broken down by its own intestinal microorganisms.
  • Lactic acid bacteria ensure an acidic environment ( pH 3.8–4.5) in the vagina and thus prevent bacterial infections (see Döderlein bacteria ).

Microorganisms as pathogens

Most microorganisms do not cause disease . Only a small proportion of the microorganisms are pathogenic , i. H. these organisms cause diseases in humans or animals (see medical microbiology ) or in plants (see phytopathology ).

The infectious diseases can also be grouped according to the type of pathogen, e.g. B. bacterial infection , fungal infection or protozoal infection .

See also

Wiktionary: microbe  - explanations of meanings, word origins, synonyms, translations
Wiktionary: microorganism  - explanations of meanings, word origins, synonyms, translations


  • Moselio Schaechter, John Ingraham, Frederick C. Neidhardt: Microbe: The original with translation aids . Spectrum Academic Publishing House, Heidelberg 2006. ISBN 3-8274-1798-8 .
  • Michael T. Madigan, John M. Martinko, Paul V. Dunlap, David P. Clark: Brock - Biology of Microorganisms , 12th Edition. Pearson, San Francisco et al. a. O. 2009, ISBN 0-321-53615-0 .
  • Georg Fuchs (ed.): General microbiology . 9th edition. Thieme, Stuttgart 2014, 9th edition 2014, ISBN 978-3-13-444609-8 .
  • Heribert Cypionka : Fundamentals of Microbiology . 4th edition. Springer, Heidelberg a. a. O. 2010, ISBN 978-3-642-05095-4 (print), ISBN 978-3-642-05096-1 (electronic).

Popular science

  • Gerhard Gottschalk : World of Bacteria. The invisible rulers of our planet. Wiley-VCH Verlag, Weinheim 2009, ISBN 978-3-527-32520-7 .
  • Jörg Blech : Life on Humans: The History of our Settlers. Rowohlt Taschenbuch Verlag, Reinbek near Hamburg 2000, ISBN 3-499-60880-4 .
  • Idan Ben-Barak: Small miracles: the invisible power of microbes. Translated from English by Sebastian Vogel. Spektrum Akademischer Verlag, Heidelberg 2010, ISBN 978-3-8274-2465-5 . (Original English: Small Wonders - How Microbes Rule Our World. 2008).
  • Paul de Kruif : Microbe hunter. (Original edition: Microbe Hunters. Harcourt, Brace & Co., New York 1926) Orell Füssli Verlag, Zurich / Leipzig 1927; 8th edition in 1940.
  • Paul de Kruif: The Fight for Life. 1938.
    • German: men who conquer death. Translated by Karl Eugen Brunner. Orell Füssli Verlag, Zurich / Leipzig 1938.

Web links

Individual evidence

  1. a b c d Schülerduden Biologie, Dudenverlag, Mannheim, 7th edition 2009, p. 367 f. (Keywords: microbiology , microorganisms )
  2. Michael T. Madigan et al .: Brock Biology of Microorganisms. 13th edition, Benjamin Cummings, 2010, ISBN 978-0-321-64963-8 , p. 2: “Microorganisms […] include the viruses”, that is, viruses are microorganisms.
  3. Harald Gärtner: Biology. Basic knowledge and laws. Compact Verlag, 2009, p. 132: "Virology also falls into the field of microbiology, although viruses are not living beings and therefore not microorganisms."
  4. Wolf-Dieter Deckwer et al. (Ed.): Römpp Lexikon Biotechnologie und Gentechnik , 2nd edition 1999, p. 524, keyword microorganisms : "Viruses [...] occupy a special position. As non-cellular particles [...] they face all organisms, but are nevertheless sometimes assigned to microorganisms. "
  5. ^ Otto Dornblüth: Clinical Dictionary. Entry: microbes, microbes (1927).
  6. Duden online: Microbe and microbes
  7. Werner Köhler : Microbe (microbe). In: Werner E. Gerabek , Bernhard D. Haage, Gundolf Keil , Wolfgang Wegner (eds.): Enzyklopädie Medizingeschichte. De Gruyter, Berlin / New York 2005, ISBN 3-11-015714-4 , p. 987 f.
  8. See Paul de Kruif : Antoni van Leewuwenhoeck. The first microbe hunter. In: Paul de Kruif: Microbe hunters. (Original edition: Microbe Hunters. Harcourt, Brace & Co., New York 1926). Orell Füssli Verlag, Zurich / Leipzig 1927; 8th edition ibid. 1940, pp. 9-29.
  9. ^ T. Gold: The deep, hot biosphere. In: Proceedings of the National Academy of Sciences . Volume 89, Number 13, July 1992, pp. 6045-6049, PMID 1631089 , PMC 49434 (free full text).
  10. CL Hemme, Y. Deng, TJ Gentry, MW Fields, L. Wu, S. Barua, K. Barry, SG Tringe, DB Watson, Z. He, TC Hazen, JM Tiedje, EM Rubin, J. Zhou J. : Metagenomic insights into evolution of a heavy metal-contaminated groundwater microbial community . In: ISME J . 4, No. 5, 2010, pp. 660-672. PMID 20182523 .
  11. Bik, EM et al .: Molecular analysis of the bacterial microbiota in the human stomach . In: PNAS . 103, No. 3, 2006, pp. 732-737. PMID 16407106 .
  12. R. Froböse: When frogs fall from the sky: the craziest natural phenomena Wiley-VCH Verlags-GmbH & Co. KGaA Weinheim 2007, ISBN 978-3-527-31659-5 , p. 19 ff.