Pentachlorophenol biodegradation by Pseudomonas spp. UG25 and UG30

Eighty-nine bacterial isolates obtained by enrichment from pentachlorophenol (PCP)-contaminated soil samples were tested for PCP dechlorination activity and hybridization to pcpB (encoding PCP-4-monooxygenase) and pcpC (encoding tetrachlorohydroquinone reductive dehalogenase) gene probes synthesized by polymerase chain reaction from Flavobacterium sp. ATCC 39723 genomic DNA. Seven isolates were able to dechlorinate FCP, hybridize to both pcpB and pcpC DNA. probes, and mineralize sodium pentachlorophenate (NaPCP) at an initial concentration of 100 mu g/ml. Although the seven PCP-mineralizing isolates possessed DNA sequences homologous to the Flavobacterium pcpB and pcpC genes, restriction analysis revealed sequence differences between the isolates and the Flavobacterium PCP dechlorination genes. Two isolates, designated UG25 and UG30, with the fastest onset and highest extent of PCP mineralization were selected for further study. Both isolates were tentatively identified as Pseudomonas spy. and exhibited stoichiometric release of Cl- ions as PCP was degraded. The release of Cl- began concomitantly with PCP disappearance from the medium. Both UG25 and UG30 degraded NaPCP at a concentration of 250 mu g/ml in a minimal salt medium. Supplementation of the medium with glutamate increased the NaPCP degradation threshold of UG25 to a concentration of 300 mu g/ml but did not affect that of UG30. P-31-NMR spectra of UG25 and UG30 cell suspensions exposed to PCP showed lower intracellular ATP levels and a more acidic cytoplasmic pH relative to untreated cells. This de-energization may explain the lack of cell growth in the presence of high PCP concentrations.