Anaerobic degradation of cresols and monohydroxybenzoates

All aromatic compounds are potential substrates for microorganisms. Hence, microorganisms play an eminent role in the global carbon cycle. The present work describes the anaerobic degradation of cresols and toluene, both bulk chemicals of the petroleum industry, and the anaerobic degradation of 3-hydroxybenzoate, a model compound for degradation of lignin-monomers. Degradation pathways for these aromatic substrates are postulated on the basis of in vitro measurements of key enzymes in various, metabolically distinct bacteria. The sulfate-reducing bacterium Desulfobacterium cetonicum channels cresols and toluene into its central metabolism via a novel addition reaction; fumarate is added to the methyl group of these compounds to form benzylsuccinate or a derivative thereof. 3-Hydroxybenzoate can be degraded by a fermenting bacterium, Sporotomaculum hydroxybenzoicum, most likely via the benzoyl-CoA pathway after CoA-esterification and subsequent reductive dehydroxylation of 3-hydroxybenzoyl-CoA, or by a denitrifying bacterium, strain BoNHB via novel oxidative hydroxylation reactions. Work presented here suggests that under anaerobic conditions the prevailing redox regime constitutes the degradation pathway of a given aromatic substrates