Anaerobic degradation of 3-aminobenzoate by a newly isolated sulfate reducer and a methanogenic enrichment culture

Abstract

A new rod-shaped, gram-negative, non-sporing sulfate reducer, strain mAB1, was enriched and isolated from marine sediment samples with 3-aminobenzoate as sole electron and carbon source. Strain mAB1 degraded 3-aminobenzoate completely to CO 2 and NH 3 with stoichiometric reduction of sulfate to sulfide. Ceils contained carbon monoxide dehydrogenase, cytochromes, and sulfite reductase P582. Strain mAB1 degraded also benzoate, 4-aminobenzoate, hydroxybenzoates, and some aliphatic compounds. Besides sulfates, also sulfite was reduced with 3-aminobenzoate as electron donor, but not thiosulfate, sulfur, nitrate, or fumarate. The strain grew in sulfide-reduced mineral medium supplemented with 7 vitamins. Strain mAB1 was tentatively affiliated with the genus esulfobacterium. Experiments with dense cell supsensions showed benzoate accumulation during 3-aminobenzoate degradation under conditions of sulfate limitation or cyanide inhibition. 3-Aminobenzoate was activated to 3-aminobenzoyl-CoA by cell extracts in the presence of ATP, coenzyme A, and Mg 2+. Acitivity of 3-aminobenzoyl-CoA synthetase was 16 nmol per rain and mg protein, with a K M for 3-aminobenzoate lower than 50 gM. Cell extract of 3-aminobenzoate-grown cells activated also 3-hydroxybenzoate (31.7 nmol per rain and mg protein) and benzoate (2.3 nmol per min and mg protein), but not 2-aminobenzoate or 4-aminobenzoate. In the presence of NADH of NADPH, 3-aminobenzoyl-CoA was further metabolized to a not yet identified reduced product.<br />Freshwater enrichments with 3-aminobenzoate in the absence of an external electron acceptor led to a stable methanogenic enrichment culture consisting of three types of bacteria. 3-Aminobenzoate was degraded completely to COz and stoichiometric amounts of CH4, with intermediary acetate accumulation.