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Sulfate-reducing bacteria are those bacteria and archaea〔 that can obtain energy by oxidizing organic compounds or molecular hydrogen (H2) while reducing sulfate () to hydrogen sulfide (H2S). In a sense, these organisms "breathe" sulfate rather than oxygen in a form of anaerobic respiration. Sulfate-reducing bacteria can be traced back to 3.5 billion years ago and are considered to be among the oldest forms of microorganisms, having contributed to the sulfur cycle soon after life emerged on Earth.〔 Many bacteria reduce small amounts of sulfates in order to synthesize sulfur-containing cell components; this is known as ''assimilatory sulfate reduction''. By contrast, the sulfate-reducing bacteria considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory sulfate reduction. They use sulfate as the terminal electron acceptor of their electron transport chain. Most of them are anaerobes; however there are examples of sulfate-reducing bacteria that are tolerant of oxygen. 〔 〕 Under oxygenated conditions these bacteria switch to aerobic respiration before reducing sulfate 〔 Most sulfate-reducing bacteria can also reduce other oxidized inorganic sulfur compounds, such as sulfite, thiosulfate, or elemental sulfur (which is reduced to hydrogen sulfide). In addition, there are sulfate-reducing bacteria that can reduce fumarate, nitrate and nitrite, iron (Fe(III)) and some other metals, dimethyl sulfoxide and even oxygen.〔 ==Ecological importance and markers== Sulfate occurs widely in seawater, sediment, or water rich in decaying organic material. Sulfate-reducing bacteria are common in anaerobic environments where they aid in the degradation of organic materials.〔 In these anaerobic environments, fermenting bacteria extract energy from large organic molecules; the resulting smaller compounds such as organic acids and alcohols are further oxidized by acetogens and methanogens and the competing sulfate-reducing bacteria.〔 The toxic hydrogen sulfide is a waste product of sulfate-reducing bacteria; its rotten egg odor is often a marker for the presence of sulfate-reducing bacteria in nature.〔 〕 Sulfate-reducing bacteria are responsible for the sulfurous odors of salt marshes and mud flats. Much of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides. These metal sulfides, such as ferrous sulfide (FeS), are insoluble and often black or brown, leading to the dark color of sludge.〔 During the Permian–Triassic extinction event (250 million years ago) a severe anoxic event seems to have occurred where these forms of bacteria became the dominant force in oceanic ecosystems, producing copious amounts of hydrogen sulfide. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sulfate-reducing bacteria」の詳細全文を読む スポンサード リンク
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