Sulfate reducing bacteria
Sulfate-reducing bacteria are those bacteria and archaea that can obtain energy by oxidizing organic compounds or molecular hydrogen (H2) while reducing sulfate (SO2−
4) 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).
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