How formate dehydrogenase-lacking acetogenClostridium bovifaecisutilize formate as the sole carbon source for its acetogenic growth?

Abstract

ABSTRACTLittle is known about the growth of formate dehydrogenase-lacking acetogen on formate as sole carbon source. Here, we analyzed formate metabolism inClostridium bovifaecisstrain BXX using different concentrations of formate. The results show thatC. bovifaecisconverted formate (11.5-96 mM) into acetate with molar ratio of 2.0:1∼2.6:1 by using L-cysteine in the anaerobic medium as electron source according to the stoichiometry of acetogenesis. Genome analysis ofC. bovifaecisrevealed genes encoding anaerobic ribonucleoside triphosphate reductase (nrdDandnrdG) catalyzing the oxidation of formate to CO2while ATP is being reduced to the desoxy form. The existence ofnrdDwas verified by PCR, reverse transcription-PCR analysis and acetogenesis from formate. The process mode of acetogenesis from formate inC. bovifaecisprovides insight into the unique metabolic feature of an FDH-lacking acetogen.IMPORTANCEWood-Ljungdahl pathway (WLP) lacking formate dehydrogenase (FDH) which catalyzes CO2reduction to formate has been reported to occur acetogenesis only in the presence of formate and exogenous CO2, which seems to result from the formate-rich habitats adaptation of gastrointestinal acetogens. Here, we found FDH-lackingClostridium bovifaecisstrain BXX converted formate (11.5-96 mM) into acetate with molar ratio of 2.0:1∼2.6:1 fitting the stoichiometry of acetogenesis when using formate as the sole carbon source. CO2needed in the carbonyl branch of WLP was from the oxidation of formate to CO2catalyzed by anaerobic ribonucleoside triphosphate reductase while ATP is being reduced to the desoxy form. L-cysteine in the anaerobic medium was the electron source of WLP. The process mode of acetogenesis from formate inC. bovifaecisprovides insight into how an FDH-lacking acetogen can make a living from the simplest resources as carbon source, which has both ecological and biotechnological significance.