Effects Of Secondary Plant Metabolites On Biodegradation Of Polychlorinated Biphenyls

Polychlorinated biphenyls (PCBs), with their high hydrophobicity and chemical stability, make them persist in the environment. Studies in humans provide supportive evidence for the potential carcinogenic and noncarcinogenic effects of PCBs.There is evidence that many secondary plant metabolites (SPMEs) may act as signal molecules to trigger the bacterial ability to metabolize PCBs during the rhizoremediation process. However, the bases for the PCB rhizoremediation process are still largely unknown. The objective of this study was to determine whether and how these treatments affect PCB removal in a historically PCB-contaminated soil (one transformer storage site in Xiaoshan). The effect of several SPMEs on the biodegradation of chiral PCBs, by T29 and W5, two isolates from long-term PCB-contaminated soil, were also studies in detail. The main results are as follows:(1)The PCBs removal was significantly influenced by biphenyl, salicylic acid and L(-)-Carvone. The highest removal of dioxin-like and chiral PCBs was found in salicylic acid treatments. Naringin enhanced hexa-PCBs removal in soils, but did not improve removal of total PCBs.(2) PCB 45,95,136,149 chiral signatures in the soil clearly shifted from racemic under salicylic acid treatment. PCB 95 exhibited strong selectivity towards the second eluting enantiomer in the presence of biphenyl, L(-)-Carvone and sodium salicylate. Naringin demonstrated significant transformation of (-)-PCB149.There was a significant negative correlation between PCBs residue and EF.(3) The significant shift of 813C values observed in the presence of salicylic acid. Biphenyl, L(-)-Carvone, sodium salicylate also had marked influences on stable carbon isotope fractionation of specific PCBs. There was a significant negative correlation between PCBs residue and δ13C.(4) The bphA gene was detected in all samples. The relative abundance of bphAl, bphD.1.B, bphD.2.A and bphD.2.A/B genes were enhanced by salicylic acid treatments. The correlation between PCBs residue and bphAl gene indicated that SPMEs may promote PCB degradation by inducing PCB-degrading enzyme synthesis. The correlation between hexa-PCBs residue and bacterial abundance indicated that SPMEs may promote PCB degradation by inducing PCB-degrading microbial growth.(5) Salicylic acid and biphenyl-grown cells of strain T29 demonstrated a wide range in selectivity, favoring transformation of the first eluting enantiomer for PCB 45,91 and (+)-PCB136, 149. When grown on biphenyl, salicylic acid, carvone and pinene, W5 showed significant shift in PCBs carbon stable isotope fractionation and enantiomer fractionation.(6) In order to quantitatively assess microbial degradation, a relationship between carbon isotope ratios and residual concentrations of PCB149 was established according to Rayleigh equation. An enrichment factor, ε=-0.0266%o was obtained, which can be employed to assess microbial degradation of PCB149. A relationship between enantiomer ratios and residual concentrations of PCB149 was established according to Reitzel equation. An enrichment factor, εER= 2.2506 was obtained, which can be employed to assess microbial degradation of PCB149.