Synthesis of α-ketoglutarate by reductive carboxylation of succinate in Veillonella, Selenomonas, and Bacteroides species

Abstract

Evidence for reductive carboxylation of succinate to synthesize α-ketoglutarate was sought in anaerobic heterotrophs from the rumen and from other anaerobic habitats. Cultures were grown in media containing unlabeled energy substrates plus [14C]succinate, and synthesis of cellular glutamate with a much higher specific activity than that of cellular aspartate was taken as evidence for α-ketoglutarate synthase activity. The results indicate α-ketoglutarate synthase functions in Selenomonas ruminantium, Veillonella alcalescens, Bacteroides fragilis, Bacteroides vulgatus, Bacteroides uniformis, Bacteroides distasonis, and Bacteroides multiacidus. Evidence for this carboxylation was not found in strains representative of 10 other species.