Anaerobic biodegradation ofPara-cresol under three reducing conditions

Abstract

The anaerobic degradation ofp-cresol was studied with one sediment source under three reducing conditions—denitrifying, sulfidogenic, and methanogenic. Loss ofp-cresol (1 mM) in all the anaerobic systems took initially 3 to 4 weeks. In acclimated culturesp-cresol was degraded in less than a week.p-Cresol was completely metabolized under denitrifying, sulfidogenic, and methanogenic conditions, with formation of nitrogen gas, loss of sulfate, and formation of methane and carbon dioxide, respectively.p-Cresol metabolism proceeded throughp-hydroxybenzal-dehyde andp-hydroxybenzoate under denitrifying and methanogenic conditions. These compounds were rapidly degraded in cultures acclimated top-cresol under all three reducing conditions. These results suggest that the initial pathway ofp-cresol degradation is the same under denitryfying, sulfidogenic, and methanogenic conditions and proceeds via oxidation of the methyl substituent top-hydroxybenzaldehyde andp-hydroxybenzoate. The initial rate ofp-hydroxybenzaldehyde degradation was high in both the unacclimated cultures and in the cultures acclimated top-cresol, suggesting that this step is nonspecific. Benzoate was additionally detected as a metabolite followingp-hydroxybenzoate in the methanogenic cultures, but not in the denitrifying or sulfidogenic cultures. The degradation pathway therefore may diverge afterp-hydroxybenzoate formation depending on which electron acceptor is available.