Carbon metabolism in Eubacterium limosum: A C-13 NMR study

Carbon metabolism was studied in Eubacterium limosum, an anaerobic acetogenic bacterium. Stationary cells fermented glucose C-13(1) to acetate-2-C-13 and butyrate-2-C-13 or butyrate-4-C-13. Reductive acetogenesis was demonstrated by feeding cells with (NaHCO3)-C-13. Acetate alone was synthesized, and the doubly labelled isotopomer was the dominant product. The biosynthesis pathways for amino acids were examined, using the incorporation of C-13. With glucose-1-C-13 as substrate, the label was found mainly on the methyl groups whereas C-13 from carbonate is incorporated mainly on carbonyl groups. The pathways operating in Eubacterium limosum were delineated with reference to the biochemistry of other microbes. It was found that Eubacterium limosum incorporates carbon through acetyl-CoA and pyruvate and the reductive TCA cycle. (C) 1996 Academic Press