Atypical one-carbon metabolism of an acetogenic and hydrogenogenic Moorella thermoacetica strain

A thermophilic spore-forming bacterium (strain AMP) was isolated from a thermophilic methanogenic bioreactor that was fed with cobalt-deprived synthetic medium containing methanol as substrate. 16S rRNA gene analysis revealed that strain AMP was closely related to the acetogenic bacterium Moorella thermoacetica DSM 521T (98.3% sequence similarity). DNA–DNA hybridization showed 75.2 ± 4.7% similarity to M. thermoacetica DSM 521T, suggesting that strain AMP is a M. thermoacetica strain. Strain AMP has a unique one-carbon metabolism compared to other Moorella species. In media without cobalt growth of strain AMP on methanol was only sustained in coculture with a hydrogen-consuming methanogen, while in media with cobalt it grew acetogenically in the absence of the methanogen. Addition of thiosulfate led to sulfide formation and less acetate formation. Growth of strain AMP with CO resulted in the formation of hydrogen as the main product, while other CO-utilizing Moorella strains produce acetate as product. Formate supported growth only in the presence of thiosulfate or in coculture with the methanogen. Strain AMP did not grow with H2/CO2, unlike M. thermoacetica (DSM 521T). The lack of growth with H2/CO2 likely is due to the absence of cytochrome b in strain AMP.