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

Abstract

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.

p-cresol methylhydroxylase from a denitrifying bacterium involved in anaerobic degradation of p-cresol

“…The organism was grown with 2.8 mM p-cresol as the carbon source in the medium described by Bossert et al (1). Bacteria were grown in 11-liter batches in a New Brunswick Microferm MF-114 fermentor maintained at 30°C, aerated at 4 liters min-', and stirred at 150 rpm.…”

“…Several recent reports have described the bacterial degradation ofp-cresol under anaerobic conditions with nitrate or sulfate as the electron acceptor or degradation by methanogenic consortia (1,20,21). Catabolism appears to proceed by oxidation of the methyl group to give p-hydroxybenzoic acid with p-hydroxybenzyl alcohol and p-hydroxybenzaldehyde as intermediates.…”

“…In a bacterial consortium isolated under anaerobic conditions with nitrate as the acceptor, one of the two organisms, PC-07, was shown to convert p-cresol into p-hydroxybenzoic acid with the concomitant reduction of nitrate (1,3). Partial purification of the enzyme suggested that it was of a type similar to that from the Pseudomonas sp., containing flavin and cytochrome, although this description was considered preliminary until spectra of the purified enzyme were obtained (2).…”

Anaerobic oxidation of p-cresol mediated by a partially purified methylhydroxylase from a denitrifying bacterium

“…Pure cultures of the pCroxidizing, denitrifying isolate, PC-07, described elsewhere (4), were routinely grown in 9-liter batch cultures under strict anaerobic conditions. For growth under denitrifying conditions, a modified Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.)…”

“…A p-cresol (pCr)-utilizing, denitrifying bacterium, PC-07, has been previously isolated and described (4). The isolate is one member of a bacterial coculture comprising two denitrifying species which interdependently utilize pCr as the sole source of carbon for growth under anaerobic conditions (5).…”