engleski

PCB-transformation activity of mixed bacterial cultures in the presence of carvone and tannin

Different biphenyl-utilizing bacteria have been shown to promote degradation of polychlorinated biphenyls (PCBs). However, their use as bioaugmentation agents has been hindered by the inability of applying biphenyl as a well-known inducer of bph genes due to its adverse health effects, high cost and poor water solubility. In this study we selected two secondary plant metabolites, carvone and tannin, as potential inducing compounds and investigated their impact on the degradation of PCB mixture Aroclor 1248. For comparison, the experiment with biphenyl was performed as well. Mixed bacterial cultures used in this study (TSZ7, CONZ, BH1 and BH2) were enriched from different PCB-contaminated soils by applying a microcosm approach and stimulating the growth of biphenyl-utilizing bacteria. Reduction of the selected congeners, which was monitored by GC-MS analyses, suggested that carvone and tannin supported their transformation and that all cultures showed degrading capability toward three- to pentachlorobiphenyls. Furthermore, the effect of tested inducers was culture dependent. Thus, the cultures TSZ7 and CONZ, demonstrating a similar PCB transformation activity, showed to be the most effective in the presence of biphenyl, reducing the selected congeners in the range of 60-99%, while in the presence of tannin and carvone reduction was in the range of 40-70% and 17-53%, respectively. In contrast cultures BH1 and BH2 showed no preference regarding the tested inducers ; BH1 and BH2 reduced the selected congeners in the range of 39-71% and 55-80%, respectively. Further evidence for PCB transformation is the fact that the genes bphA (encoding the first enzyme of the bph pathway) and bphC (encoding ring-cleavage enzyme) have been identified in all tested cultures. In conclusion, the present study suggested that beside biphenyl, carvone and tannin may also induce bph catabolic pathway, which opens the possibility to develop new approaches for bioremediation of PCB-contaminated enviroment.

PCB; aerobic degradation; inducer; carvone; tannin; mixed cultures

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