Characterization of a soil bacterial community and biphenyl dioxygenase genes involved in the degradation of individual polychlorinated biphenyl congeners.

摘要

Polychlorinated biphenyls (PCBs) are widespread, toxic, and persistent contaminants that threaten the environment and human health. PCBs represent a class of 209 congeners characterized by different degree of chlorination and substitution patterns. PCBs are known to be slowly degraded by the activity of soil microbes.;The general objective of this research was to investigate the effect of individual PCB congeners on the bacterial community and aerobic metabolism of PCBs in soil, for this reason three specific aims were pursuit.;The first specific aim was to test the hypothesis that exposure to individual PCB congeners results in different soil microbial community profiles, as well as different abundances of biphenyl dioxygenase (BPH) genes; experiments on soil microcosm were conducted using aerobic agitated soil slurries individually exposed to specific PCB congeners. It was observed that exposure to different PCB congeners modifies the structure of the microbial community resulting in higher representation of phyla involving PCB degraders and higher number of biphenyl dioxygenase genes, bph.;The second specific aim focused on the characterization of the soil microbial community in contaminated soil samples from a heavily PCB-contaminated site, the Confined Disposal Facility (CFD) in South Chicago, Indiana. For this reason, terminal-restriction fragment length polymorphism (T-RFLP) analyses were carried out. The results provide preliminary evidence of a correlation between the microbial communities and the PCBs profiles.;The last specific aim was to determine the potential toxicity of a selected group of PCB congeners and hydroxyl metabolites on pure cultures of Escherichia coli and Burkholderia xenovorans LB400. Preliminary results showed that exposure of pure bacteria culture to individual PCBs and their hydroxyl metabolites products resulted in different inhibition of bacterial growth. A significant impact on the bacterial growth was found when B. xenovorans LB400 was exposed to the PCB-3 metabolite, 4'-OH-PCB-35. Likewise, it was found that B. xenovorans LB400 took a long period of time to acclimate to metabolites of PCB-3, which included 2'-OH-PCB-3, 3'-OH-PCB-3, and 4'-OH-PCB-3.