Isolation and characterization of several novel PCB-degrading isolates from contaminated soil

Several isolates were obtained from the polychlorinated biphenyl (PCB)-contaminated soil by enrichment in a phosphate-buffered mineral salts medium (PAS) supplemented with PCB and biphenyl/chloro benzoic acids as sole carbon source. The isolates were identified as Pseudomonas aurofaciens, Bacillus macerens, Bacillus cereus, and Arthobacter uratoxydens by Microbial Identification System and Biolog Metabolic Identification System. These isolates were characterized for gram reaction, oxidase, colony morphology, catalase activity, motility, and 2,3 dihydroxybiphenyl reaction. The performance of these isolates was compared with well-characterized PCB-degrading strains of Alcaligenes eutrophus H 850 and Pseudomonas sp. LB 400 for degradation of PCB congeners. One of the isolates, Pseudomonas aurofaciens, has demonstrated better PCB-degradative ability than any other PCB-degrading organism reported to date. These isolates did not produce the meta cleavage product with 2,3-dihydroxybiphenyl suggesting a possible involvement of a different degradative pathway. On the other hand, the colonies of Alcaligenes eutrophus H850 and Pseudomonas sp. LB 400 showed a positive reaction as evidenced by yellow metabolite, 2-hydroxy-6-oxo-6-phenyl-hexa-2,4-dienoic acid. Mineralization studies conducted with C-14-radiolabelled compounds of 2-chlorobiphenyl and 2,2',4,4'-tetrachlorobiphenyl showed <4% mineralization with growing cultures as compared to >40% with resting cells of these isolates. The known strains showed similar pattern of degradation with growing and resting cells. These findings suggest that these isolates appear to possess unique ability to degrade PCB and can possibly be employed in complement to other PCB degraders.