Polychlorinated biphenyl degradation activities and hybridization analysesof fifteen aerobic strains isolated from a PCB-contaminated site

Fifteen bacterial strains using biphenyl as sole carbon and energy source, obtained from different positions and depths of a polychlorinated biphenyl (PCB)-contaminated area, were analyzed for their basic metabolic phenotypes and subjected to genomic DNA hybridization screening for the presence of w ell characterized bph operons such as those of Pseudomonas pseudoalcaligene s KF707 and Rhodococcus globerulus P6. Most of the isolates belonged to the gamma -subdivision (Pseudomonas stutzeri, P. putida, P. fluorescens and Vi brio logei species) and to the beta -subdivision (genera Alcaligenes, Comam onas, Ralstonia) of the Proteobacteria. All the isolates were able to comet abolize different low chlorinated PCB congeners. Among the dichlorinated bi phenyls tested, a lower degradation capacity was observed for the di-ortho substituted congeners, whereas high levels of degradation were observed for the di-meta and di-para isomers, whether they were chlorinated on one or o n both rings. The PCB congeners nonsubstituted in the 2,3 or 2,3 and 3,4 po sitions were also degraded by most of the isolated strains, which were, how ever, unable to significantly metabolize PCBs with more than 3 chlorine ato ms. Five of the isolated strains were also able to degrade some of the tri- and tetrachlorobiphenyls tested. Southern hybridization analysis showed a strong homology between four of the fifteen isolated strains and the bph op eron obtained from P. pseudoalcaligenes strain KF707. Conversely, none of t he isolates here examined showed homology with the bph operon of R. globeru lus strain P6. In line with this, the KF707 bph probe strongly hybridized w ith DNA of a significant number of bacterial colonies obtained from selecte d locations in the contaminated area using biphenyl-supplemented minimal me dium agar plates. (C) 2001 Editions scientifiques et medicales Elsevier SAS .