p-Cresol biodegradation under denitrifying conditions: isolation of a bacterial coculture

From polluted river sediment, two bacterial species were isolated which utilized p-cresol as the sole source of carbon when grown in coculture under nitrate-reducing conditions. One species, PC-07, metabolized p-cresol (pCr) anaerobically to p-hydroxybenzoate (pOHB), which in turn was further metabolized by the second isolate, PB-04. The PC-07 isolate was unable to degrade and utilize pOHB, and PB-04 was unable to utilize pCr, thereby demonstrating a syntrophic relationship for pCr utilization under anaerobic conditions. Nitrate served as external electron acceptor for both microorganisms under anaerobic conditions and was reduced via NO₂⁻ and N₂O to N₂. pCr, therefore, appears to be metabolized to ring fission products via the formation of pOHB under nitrate reducing conditions, with the metabolism being mediated by a 2-member microbiol food chain.