Reverse Krebs cycle

⭐ Core Definition: Reverse Krebs cycle

The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle, or the reductive tricarboxylic acid cycle, or the reductive TCA cycle) is a sequence of chemical reactions that are used by some bacteria and archaea to produce carbon compounds from carbon dioxide and water by the use of energy-rich reducing agents as electron donors.

The reaction is the citric acid cycle run in reverse. Where the Krebs cycle takes carbohydrates and oxidizes them to CO₂ and water, the reverse cycle takes CO₂ and H₂O to make carbon compounds.This process is used by some bacteria (such as Aquificota) to synthesize carbon compounds, sometimes using hydrogen, sulfide, or thiosulfate as electron donors. This process can be seen as an alternative to the fixation of inorganic carbon in the Calvin cycle which occurs in a wide variety of microbes and higher organisms.

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Reverse Krebs cycle in the context of 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).

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. Additionally, unlike its oxygenic counterpart that predominantly uses chlorophyll, this type of photosynthesis uses the bacteriochlorophyll (BChl) to utilize light as an energy source. 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.

View the full Wikipedia page for Anoxygenic photosynthesis

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⭐ Core Definition: Reverse Krebs cycle

Reverse Krebs cycle in the context of Anoxygenic photosynthesis