ANAEROBIC BIODEGRADATION OF PARA-CRESOL UNDER 3 REDUCING CONDITIONS

The anaerobic degradation of p-cresol was studied with one sediment source under three reducing conditions-denitrifying, sulfidogenic, and methanogenic. Loss of p-cresol (1 mM) in all the anaerobic systems took initially 3 to 4 weeks. In acclimated cultures p-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 through p-hydroxybenzal-dehyde and p-hydroxybenzoate under denitrifying and methanogenic conditions. These compounds were rapidly degraded in cultures acclimated to p-cresol under all three reducing conditions. These results suggest that the initial pathway of p-cresol degradation is the same under denitryfying, sulfidogenic, and methanogenic conditions and proceeds via oxidation of the methyl substituent to p-hydroxybenzaldehyde and p-hydroxybenzoate. The initial rate of p-hydroxybenzaldehyde degradation was high in both the unacclimated cultures and in the cultures acclimated to p-cresol, suggesting that this step is nonspecific. Benzoate was additionally detected as a metabolite following p-hydroxybenzoate in the methanogenic cultures, but not in the denitrifying or sulfidogenic cultures. The degradation pathway therefore may diverge after p-hydroxybenzoate formation depending on which electron acceptor is available. © 1990 Springer-Verlag New York Inc.