| Adding plant secondary metabolites to induce polychlorinated biphenyl (PCB) degradation and using surfactant to increase PCB bioavailability are promising bioremediation strategies. However, these strategies were rarely tested in soils and the related microbial population changes were unknown. The effects of potential inducers (biphenyl and several plant secondary metabolites) and surfactant (hydroxypropyl-beta-cyclodextrin [HP-beta-CD]) on PCB removal and microbial population changes were investigated in two soils. Biphenyl, but not plant secondary metabolites or HP-beta-CD, enhanced lower chlorinated PCB removal in two soils differing in organic matter content. HP-beta-CD decreased PCB removal when used in combination with biphenyl. HP-beta-CD increased Gram-negative bacteria and decreased Gram-positive bacteria as indicated by phospholipid fatty acid (PLFA) community analysis. There was no significant correlation between PCB removal and any PLFA. In a second study, the objectives were to isolate PCB-degrading bacteria from experimental soils, and characterize them for their phylogenetic identity and PCB-transforming properties. Two PCB-degraders were isolated and identified as Ralstonia eutropha (WL7B) and Burkholderia cepacia (FL5B). WL7B, but not FL5B, possessed 2,3-dihydroxybiphenyl dioxygenase (DHBDO) activity (a indicator of PCB degradation pathway). DHBDO reaction was substrate inhibited; however, inhibition was alleviated by amending culture with organic carbon and increasing cell density. PCB removal by both isolates was higher in glucose than in soil extract media, and was enhanced by biphenyl and HP-beta-CB. The influence of potential inducers on PCB removal by microbial populations from terrestrial and aquatic environmental was compared. Biphenyl enhanced PCB removal by organisms from aquatic sediments, but not by organisms from terrestrial soils. Amendments caused significant changes in microbial populations; however, these were not related to PCB removal, as indicated by denaturing gradient gel electrophoresis (DGGE). In conclusion, plant secondary metabolites did not appear to enhance PCB removal in soils. HP-beta-CB increased or decreased PCB removal depending on co-amendments and experimental conditions. Microbial population changes were detected by PLFA and DGGE methods, however, they did not correlate well with PCB removal. |
