ANAEROBIC DEGRADATION OF CATECHOL BY DESULFOBACTERIUM SP STRAIN CAT2 PROCEEDS VIA CARBOXYLATION TO PROTOCATECHUATE

Under anoxic conditions, most methoxylated mononuclear aromatic compou nds are degraded by bacteria, with catechol being formed as an importa nt intermediate. On the basis of our experiments with the sulfate-redu cing bacterium Desulfobacterium sp. strain Cat2, we describe for the f irst time the enzymatic activities involved in the complete anaerobic oxidation of catechol and protocatechuate. Results obtained from exper iments with dense cell suspensions of strain Cat2 demonstrated that al l enzymes necessary for protocatechuate and benzoate degradation were induced during growth with catechol. In addition, anaerobic oxidation of catechol was found to be a CO2-dependent process. Phenol was not de graded in suspensions of cells grown vith catechol. In cell extracts o f Desulfobacterium sp. strain Cat2, protocatechuyl-coenzyme A (CoA) wa s formed from catechol, bicarbonate, and uncombined CoA. This oxygen-s ensitive reaction requires high concentrations of both bicarbonate and protein, and only very low levels of enzyme were detected. In a secon d oxygen-sensitive step, protocatechuyl-CoA was reduced to 3-hydroxybe nzoyl-CoA by reductive elimination of the p-hydroxyl group. Further de hydroxylation to benzoyl-CoA was not detectable. Key reactions describ ed for anaerobic degradation of benzoate were catalyzed by cell extrac ts of strain Cat2, too.