Sulfate-reducing bacteria (SRB) are those bacteria and archaea that can obtain energy by oxidizing organic compounds while reducing sulfate (SO42-) to hydrogen sulfide (H2S).In a sense, these organisms "breathe" sulfate rather than oxygen by 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 on Earth. Species of SRB’s can tolerate temperatures exceeding 90°C and more than 100 bar pressure.
The main nutrients for SRB are simple organic acids and molecular hydrogen (H2) from decomposing natural organic matter. The nutrients are oxidized, with sulfate being reduced to sulfide (hydrogen sulfide, H2S). The formed H2S is the principal agent in the disastrous effects caused by SRB. It contaminates gas and stored oil, precipitates ferrous sulfide that plugs injection wells, and promotes precipitates ferrous sulfide that plugs injection wells, and promotes corrosion of iron and steel in the absence of oxygen (anaerobic corrosion).