Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O 2 ). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environments with an oxygen concentration greater than 0.5%.
17-667: The plasmodiophores (also known as plasmophorids or plasmodiophorids ) are a group of obligate endoparasitic protists belonging to the subphylum Endomyxa in Cercozoa . Taxonomically, they are united under a single family Plasmodiophoridae , order Plasmodiophorida , sister to the phagomyxids . Plasmodiophores are pathogenic for a wide range of organisms, but mainly green plants . The more commonly recognized are agents of plant diseases such as clubroot , powdery scab and crook root of watercress , or vectors for viruses that infect beets , peanut , monocots and potatoes , such as
34-454: A polyphyletic phylum called Opalozoa, which at the time contained a diverse assemblage of unrelated zooflagellates, opalines and proteomyxids . Eventually this phylum was discarded, and the name Opalozoa was modified to label a group inside the phylum Bigyra containing the opalines , bicosoecids and related organisms. Finally, after phylogenetic analyses, in 2002 Cavalier-Smith placed all Phytomyxea , including plasmodiophores, in
51-541: A symbiosis See also [ edit ] Opportunism (biological) Retrieved from " https://en.wikipedia.org/w/index.php?title=Obligate&oldid=1151101421 " Category : Biology terminology Obligate anaerobe The oxygen sensitivity of obligate anaerobes has been attributed to a combination of factors including oxidative stress and enzyme production. Oxygen can also damage obligate anaerobes in ways not involving oxidative stress. Because molecular oxygen contains two unpaired electrons in
68-400: A parasitic microorganism that cannot reproduce without entering a suitable host cell Obligate parasite , a parasite that cannot reproduce without exploiting a suitable host Obligate photoperiodic plant , a plant that requires sufficiently long or short nights before it initiates flowering, germination or similarly functions Obligate symbionts , organisms that can only live together in
85-546: A redox potential lower than -0.3 V. Sulfide is an essential component of some enzymes, and molecular oxygen oxidizes this to form disulfide , thus inactivating certain enzymes (e.g. nitrogenase ). Organisms may not be able to grow with these essential enzymes deactivated. Growth may also be inhibited due to a lack of reducing equivalents for biosynthesis because electrons are exhausted in reducing oxygen. Obligate anaerobes convert nutrients into energy through anaerobic respiration or fermentation . In aerobic respiration,
102-491: A term used in fish physiology to describe those that respire entirely from the atmosphere Obligate biped, Bipedalism designed to walk on two legs Obligate carnivore , an organism dependent for survival on a diet of animal flesh. Obligate chimerism , a kind of organism with two distinct sets of DNA, always Obligate hibernation , a state of inactivity in which some organisms survive conditions of insufficiently available resources. Obligate intracellular parasite ,
119-490: Is thought to reflect the quantity of superoxide dismutase and catalase being produced. In 1986, Carlioz and Touati performed experiments which support the idea that reactive oxygen species may be toxic to anaerobes. E. coli , a facultative anaerobe, was mutated by a deletion of superoxide dismutase genes. In the presence of oxygen, this mutation resulted in the inability to properly synthesize certain amino acids or use common carbon sources as substrates during metabolism. In
136-730: The highest occupied molecular orbital , it is readily reduced to superoxide ( O 2 ) and hydrogen peroxide ( H 2 O 2 ) within cells. A reaction between these two products results in the formation of a free hydroxyl radical (OH ). Superoxide, hydrogen peroxide, and hydroxyl radicals are a class of compounds known as reactive oxygen species (ROS), highly reactant products that are damaging to microbes, including obligate anaerobes. Aerobic organisms produce superoxide dismutase and catalase to detoxify these products, but obligate anaerobes produce these enzymes in very small quantities, or not at all. The variability in oxygen tolerance of obligate anaerobes (<0.5 to 8% O 2 )
153-476: The potato mop-top virus or the beet necrotic yellow vein virus . The plasmodiophores have historically been regarded as Fungi . The first description of plasmodiophores as a taxonomic group was in 1885 by Zopf , who united two genera Plasmodiophora and Tetramyxa in a common family “Plasmodiophoreæ”, inside the group “Monadineæ”, as part of the division Myxomycetes . The family was renamed “Plasmodiophoraceae” in 1888 by Berlese . In 1892, Engler placed
170-524: The absence of oxygen, the mutated samples grew normally. In 2018, Lu et al. found that in Bacteroides thetaiotaomicron , an obligate anaerobe found in the mammalian digestive tract, exposure to oxygen results in increased levels of superoxide which inactivated important metabolic enzymes. Dissolved oxygen increases the redox potential of a solution, and high redox potential inhibits the growth of some obligate anaerobes. For example, methanogens grow at
187-513: The deep ocean, still waters, landfills, in deep sediments of soil. Examples of obligately anaerobic bacterial genera include Actinomyces , Bacteroides , Clostridium , Fusobacterium , Peptostreptococcus , Porphyromonas , Prevotella , Propionibacterium , and Veillonella . Clostridium species are endospore -forming bacteria, and can survive in atmospheric concentrations of oxygen in this dormant form. The remaining bacteria listed do not form endospores. Several species of
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#1733085796249204-429: The family in its own class “Plasmodiophorales”, later renamed “Plasmodiophoromycetes” to fit nomenclature standards . In 1969 Whittaker , in his five-kingdom system , elevated the group to a separate phylum “Plasmodiophoromycota”, acknowledging them as protists instead of fungi. In 1993 Cavalier-Smith included the plasmodiophores and their sister group Phagomyxida in their current class, Phytomyxea , as part of
221-459: The 💕 [REDACTED] Look up obligate in Wiktionary, the free dictionary. As an adjective, 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-breather,
238-412: The number of ATP molecules generated) is less than in aerobic respiration. This is why facultative anaerobes , which can metabolise energy both aerobically and anaerobically, preferentially metabolise energy aerobically. This is observable when facultative anaerobes are cultured in thioglycolate broth . Obligate anaerobes are found in oxygen-free environments such as the intestinal tracts of animals,
255-423: The pyruvate generated from glycolysis is broken down without the involvement of an electron transport chain (i.e. there is no oxidative phosphorylation ). Numerous fermentation pathways exist such as lactic acid fermentation , mixed acid fermentation , 2-3 butanediol fermentation where organic compounds are reduced to organic acids and alcohol. The energy yield of anaerobic respiration and fermentation (i.e.
272-526: The pyruvate generated from glycolysis is converted to acetyl-CoA . This is then broken down via the TCA cycle and electron transport chain . Anaerobic respiration differs from aerobic respiration in that it uses an electron acceptor other than oxygen in the electron transport chain. Examples of alternative electron acceptors include sulfate , nitrate , iron , manganese , mercury , and carbon monoxide . Fermentation differs from anaerobic respiration in that
289-517: The subphylum Endomyxa , inside the rhizarian phylum Cercozoa . The number of genera varies between sources. There are three accepted genera in the group according to the WoRMS register: Plasmodiophora , Spongospora and Tetramyxa . Below is a complete list with genera that are not included in the register but appear in relevant sources: These genera were once considered plasmodiophores until they were excluded: Obligate From Misplaced Pages,
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