Anaerobic degradation of malonate via malonyl-CoA by Sporomusa malonica, Klebsiella oxytoca, and Rhodobacter capsulatus.

Anaerobic decarboxylation of malonate to acetate was studied with Sporomusa malonica, Klebsiella oxytoca, and Rhodobacter capsulatus. Whereas S. malonica could grow with malonate as sole substrate (Y = 2.0 g.mol-1), malonate decarboxylation by K. oxytoca was coupled with anaerobic growth only in the presence of a cosubstrate, e.g. sucrose or yeast extract (Ys = 1.1-1.8 g.mol malonate-1). R. capsulatus used malonate anaerobically only in the light, and growth yields with acetate and malonate were identical. Malonate decarboxylation in cell-free extracts of all three bacteria was stimulated by catalytic amounts of malonyl-CoA, acetyl-CoA, or Coenzyme A plus ATP, indicating that actually malonyl-CoA was the substrate of decarboxylation. Less than 5% of malonyl-CoA decarboxylase activity was found associated with the cytoplasmic membrane. Avidin (except for K. oxytoca) and hydroxylamine inhibited the enzyme completely, EDTA inhibited partially. In S. malonica and K. oxytoca, malonyl-CoA decarboxylase was active only after growth with malonate; malonyl-CoA: acetate CoA transferase was found as well. These results indicate that malonate fermentation by these bacteria proceeds via malonyl-CoA mediated by a CoA transferase and that subsequent decarboxylation to acetyl-CoA is catalyzed, at least with S. malonica and R. capsulatus, by a biotin enzyme.