Wood–Ljungdahl pathway

For example, sulfate-reducing bacteria (SRB) transform acetate completely into CO2 and H2 coupled with the reduction of sulfate to sulfide.

[6] In these anaerobic archaea, the Wolfe Cycle functions as a methanogenesis pathway to reduce CO2 into methane (CH4) with electron donors such as hydrogen (H2) and formate (HCOO–).

[10] Joseph Moran and colleagues state that "it has been proposed that either the complete or “horseshoe” forms of the rTCA cycle may have once been united with the acetyl CoA pathway in an ancestral, possibly prebiotic, carbon fixation network".

[9] A 2016 study of the genomes of a set of bacteria and archaea suggested that the last universal common ancestor (LUCA) of all cells was using an ancient Wood–Ljungdahl pathway in a hydrothermal setting,[11] but more recent work challenges this conclusion as they argued that the previous study had "undersampled protein families, resulting in incomplete phylogenetic trees which do not reflect protein family evolution".

[12] However geological evidence and phylogenomic reconstructions of the metabolic network of the common ancestors of archaea and bacteria support that LUCA fixed CO2 and relied on H2.