General Microbiology - Schlegel, H. 1987

Electron transport under anaerobic conditions
Acetate formation during carbonate reduction

In various methane-producing environments, acetic acid is also formed. The acidification of the medium in wastewater Treatment sludge tanks is likely associated with The activity of Bacteria that convert СO₂ and molecular hydrogen into acetic acid According to the equation

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By accumulation in a medium containing only essential inorganic salts and Vitamins, sparged with Н₂ and СO₂, researchers successfully isolated bacteria capable of autotrophic growth in the presence of Н₂ and СO₂ from hydrogen sulfide sludge, freshwater sediments, and marine muds. These are Gram-positive rod-shaped bacteria, such as Clostridium aceticum, C. thermoaceticum, and Acetobacterium woodii (Section 8.6). Acetogenic bacteria should be classified as anaerobic chemolithoautotrophic, hydrogen-oxidizing microorganisms that derive energy via a specific type of Anaerobic Respiration, namely carbonate respiration. Their cellular carbon assimilation pathway proceeds via acetyl-CoA and Pyruvate. In this pathway of acetate synthesis, СO₂ is reduced via a formate intermediate, utilizing tetrahydrofolic acid as a coenzyme, to methyl-РН₄. Subsequent transformations are presumably similar to the steps of acetate synthesis in Methanobacterium thermoautotrophicum. The reductive carboxylation of acetyl-CoA leads to The formation of pyruvate, from which cellular components are subsequently synthesized through standard metabolic pathways.

Bacteria capable of carbonate respiration secrete large amounts of acetic acid when grown on media supplemented with Н₂ and СО₂. It can be hypothesized that this formation proceeds via the assimilatory acetate synthesis pathway and that the high-energy bond in acetyl-CoA is utilized for ATP regeneration. However, the precise mechanism of these transformations remains incompletely understood and has not been elucidated for all species.