Anoxygenic photosynthesis

Anoxygenic photosynthesis is a special form of photosynthesis used by some bacteria and archaea, which differs from the better known oxygenic photosynthesis in plants and cyanobacteria in the reductant used (e.g. hydrogen sulfide instead of water) and the byproduct generated (e.g. elemental sulfur instead of molecular oxygen).^[1][2][3][4]

Unlike oxygenic phototrophs that only use the Calvin cycle to fix carbon dioxide, anoxygenic phototrophs can use both the Calvin cycle and the reverse TCA cycle to fix carbon dioxide.^[2][5] Additionally, unlike its oxygenic counterpart that predominantly uses chlorophyll, this type of photosynthesis uses the bacteriochlorophyll (BChl) to utilize light as an energy source.^[6] A precursor to oxygenic photosynthesis but having been developed after chemolithoautotrophy, anoxygenic photosynthesis uses one of two reaction centers while oxygenic photosynthesis uses both type I and type II reaction centers.^[1]