Transient production of formate during chemolithotrophic growth of anaerobic microorganisms on hydrogen

The homoacetogenic bacteria Acetobacterium woodii, A. carbinolicum, Sporomu sa ovata, and Eubacterium limosum, the methanogenic archaeon Methanobacteri um formicicum, and the sulfate-reducing bacterium Desulfotomaculum orientis all produced formate as an intermediate when they were growing: chemolitho autotrophically with H-2 and CO2 as sources of energy, electrons, and carbo n. The sulfate-reducing bacterium Desulfovibrio vulgaris grew chemolithohet erotrophically with H-2 and CO2 using acetate as carbon source, but also pr oduced formate when growth was limited by sulfate. All these bacteria were also able to grow on formate as energy source. Formate accumulated transien tly while H-2 was consumed. The maximum formate concentrations measured in cultures of A. woodii and A. carbinolicum were proportional to the initial H-2 partial pressure, giving a ratio of about 0.5 mM formate per 10 kPa H-2 . The methanogen Methanobacterium bryantii, on the other hand, was unable t o grow on formate and did not produce formate during chemolithoautotrophic growth on HZ The results indicate that the ability to utilize formate, that is, to possess a formate dehydrogenase, was the precondition for the produ ction of formate during chemolithotrophic growth on Hz.