Obligate anaerobe


Obligate anaerobe
Aerobic and anaerobic bacteria can be identified by growing them in liquid culture:
1. Obligate aerobe
2. Obligate anaerobe
3. Facultative anaerobic organism (continuum with "Facultative aerobic organism")
4. Microaerophile
5. Aerotolerant organism

Obligate anaerobes are microorganisms that live and grow in the absence of molecular oxygen; some of these are killed by oxygen. (adj., anaero´bic., adj.)[1]

Contents

Metabolism

Historically, it was widely accepted[citation needed] that obligate (strict) anaerobes die in presence of oxygen due to the absence of the enzymes superoxide dismutase and catalase, which would convert the lethal superoxide formed in their cells due to the presence of oxygen. While this is true in some cases, these enzyme activities have been identified in some obligate anaerobes, and genes for these enzymes and related proteins have been found in their genomes, such as Clostridium butyricum and Methanosarcina barkeri, among others. However, these organisms are still incapable of growing in the presence of oxygen. There are several hypotheses addressing why strict anaerobes are sensitive to oxygen:

  1. Dissolved oxygen increases the redox potential of a solution, and high redox potential inhibits the growth of some strict anaerobes. For example, methanogens grow at a redox potential lower than -0.3 V.
  2. Sulfide is an essential component of some enzymes, and molecular oxygen oxidizes this to form disulfide, thus inactivating certain enzymes. Organisms may not be able to grow without these deactivated enzymes.
  3. Growth may be inhibited due to a lack of reducing equivalents for biosynthesis, because electrons are exhausted in reducing oxygen.

It is most likely a combination of these mechanisms that accounts for oxygen sensitivity in obligate anaerobes.[2]

Instead of oxygen, obligate anaerobes use alternate electron acceptors for cellular respiration such as sulfate, nitrate, iron, manganese, mercury, and carbon monoxide. The energy yield of these respiratory processes is less than oxygen respiration, and not all of these electron acceptors are created equal.

  • In marine sediments large amounts of sulfate-reducing bacteria causes the rotten egg smell and black material that can be found just a few centimeters below the sediment surface.

Examples

Bacteroides and Clostridium species are examples of non-spore forming and spore-forming strict anaerobes, respectively.

Other obligate anaerobes include Peptostreptococcus, Veillonella,[3] and Actinomyces.

See also

References

  1. ^ "anaerobe" at Dorland's Medical Dictionary
  2. ^ Kim, Byung Hong and Geoffrey Michael Gadd. Bacterial Physiology and Metabolism. Cambridge University Press, Cambridge, UK. 2008.
  3. ^ "ANAEROBIC BACILLI". http://www1.indstate.edu/thcme/micro/lectures/anaerlec.html. Retrieved 2009-03-10. [dead link]

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Look at other dictionaries:

  • obligate anaerobe — noun an organism that cannot grow in the presence of oxygen • Hypernyms: ↑anaerobe …   Useful english dictionary

  • obligate anaerobe — a microorganism that can grow only in the complete absence of molecular oxygen; some are killed by oxygen …   Medical dictionary

  • Obligate — means by necessity (antonym facultative) and is used mainly in biology in phrases such as: Obligate aerobe, an organism that cannot survive without oxygen Obligate anaerobe, an organism that cannot survive in the presence of oxygen Obligate air… …   Wikipedia

  • anaerobe — A microorganism that can live and grow in the absence of oxygen. [G. an priv. + aer, air, + bios, life] facultative a. an a. that either grows in the presence of air or under conditions of reduced oxygen tension. obligate a. an a. that will grow… …   Medical dictionary

  • Obligate aerobe — Aerobic and anaerobic bacteria can be identified by growing them in liquid culture: 1. Obligate aerobe 2. Obligate anaerobe 3. Facultative anaerobic organism (continuum with Facultative aerobic organism ) 4. Microaerophile 5. Aerotolerant An… …   Wikipedia

  • anaerobe — n. any organism, especially a microbe, that is able to live and grow in the absence of free oxygen. A facultative anaerobe is a microorganism that grows best in the presence of oxygen but is capable of some growth in its absence. An obligate… …   The new mediacal dictionary

  • obligate — obligable /ob li geuh beuhl/, adj. obligator, n. v. /ob li gayt /; adj. /ob li git, gayt /, v. obligated, obligating, adj. v.t. 1. to bind or oblige morally or legally: to obligate oneself to purchase a building. 2. to pledge, commit, or bind… …   Universalium

  • obligate — 1. verb /ˈɑblɪɡeɪt,ˈɑblɪɡət,ˈɒblɪɡeɪt,ˈɒblɪɡət/ a) To bind, compel, or constrain by a social, legal, or moral tie. See Synonyms at force. b) To cause to be grateful or indebted; to …   Wiktionary

  • Anaerobe Atmung — Anaerobie (aus dem altgriechischen Präfix an „ohne, nicht“ und ἀήρ „Luft“) ist das Gegenteil von Aerobie. Als anaerob werden Atemprozesse bezeichnet, die keinen elementaren, molekularen Sauerstoff (O2) benötigen. Solche Lebewesen, die für ihren… …   Deutsch Wikipedia

  • Анаэроб (Anaerobe) — любой микроорганизм, особенно микроб, который способен жить, расти и развиваться при отсутствии свободного кислорода. Факультативный анаэроб (facultative anaerobe) представляет собой микроорганизм, который лучше растет при наличии в окружающей… …   Медицинские термины


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