ANAEROBIC DEGRADATION OF MALONATE VIA MALONYL-COA BY SPOROMUSA-MALONICA, KLEBSIELLA-OXYTOCA, AND RHODOBACTER-CAPSULATUS

Anaerobic decarboxylation of malonate to acetate was studied with Spor omusa malonica, Klebsiella oxytoca, and Rhodobacter capsulatus. Wherea s S. malonica could grow with malonate as sole substrate (Y = 2.0 g.mo l(-1)), malonate decarboxylation by K. oxytoca was coupled with anaero bic growth only in the presence of a cosubstrate, e.g. sucrose or yeas t extract (Y-s = 1.1-1.8 g.mol malonate(-1)). R. capsulatus used malon ate anaerobically only in the light, and growth yields with acetate an d malonate were identical. Malonate decarboxylation in cell-free extra cts of all three bacteria was stimulated by catalytic by catalytic amo unts of malonyl-CoA, acetyl-CoA, or Coenzyme A plus ATP, indicating th at actually malonyl-CoA was the substrate of decarboxylation. Less tha n 5% of malonyl-CoA decarboxylase activity was found associated with t he cytoplasmic membrane. Avidin (except for K. oxytoca) and hydroxylam ine inhibited the enzyme completely, EDTA inhibited partially. In S. m alonica and K. oxytoca, malonyl-CoA decarboxylase was active only afte r growth with malonate; malonyl-CoA: acetate CoA transferase was found as well. These results indicate that malonate fermentation by these b acteria proceeds via malonyl-CoA mediated by a CoA transferase and the subsequent decarboxylation to acetyl-CoA is catalyzed, at least with S. malonica and R. capsulatus, By a biotin enzyme.