Biodegradation of seven polychlorinated biphenyls by a newly isolated aerobic bacterium (Rhodococcus sp. R04)

Abstract

An aerobic bacterial strain, designated R04, belonging to the genus Rhodococcus has been isolated and characerized by 16S rDNA analysis. The capability of this strain to degrade seven different polychlorinated biphenyls (CBs), 500 ppm 3-CB, 3,4-CB, 4,4'-CB, 2,4,6-CB, 2,4',5-CB, 2,3,4,5-CB and 3,4,3',4'-CB in liquid medium, was evaluated. After 5 days of incubation, the concentration of chloride increased to 0.35 mM in cultures containing 3-CB and R04, whereas in cultures with 3,4-CB, 2,3,4,5-CB or 3,4,3',4'-CB plus R04 the chloride content increased to 0.1 mM. However, non-stoichiometric amounts of chloride were produced in cultures with R04 and 4,4'-CB, 2,4,6-CB and 2,4',5-CB. The spectrum of supernatants from R04 grown on seven PCBs had a UV-visible (UV-VIS) absorption at 200-500 nm, characteristic of biphenyl-derived cleavage products. Gas-chromatographic (GC) analysis showed that R04 was able to transform 100% of 3-CB and 3,4-CB after 1 day of incubation, and 95% of 4,4'-CB, 2,4,6-CB, 2,4',5-CB, 2,3,4,5-CB and 3,4,3',4'-CB after 5 days of incubation. The position of the chlorine substituents on the rings strongly influenced the degradation of polychlorinated biphenyls (PCBs) and their intermediate metabolites by Rhodococcus sp. R04. The degradation of PCBs was further evaluated by monitoring intermediate metabolites of PCBs.