MOLECULAR DIAGNOSTICS AND CHEMICAL-ANALYSIS FOR ASSESSING BIODEGRADATION OF POLYCHLORINATED-BIPHENYLS IN CONTAMINATED SOILS

The microbial populations in PCB-contaminated electric power substatio n capacitor bank soil (TVA soil) and from another PCB-contaminated sit e (New England soil) were compared to determine their potential to deg rade PCB. Known biphenyl operon genes were used as gene probes in colo ny hybridizations and in dot blots of DNA extracted from the soil to m onitor the presence of PCB-degrading organisms in the soils. The micro bial populations in the two soils differed in that the population in N ew England soil was enriched by the addition of 1000 p.p.m. 2-chlorobi phenyl (2-CB) whereas the population in the TVA capacitor bank soil wa s not affected. PCB degradative activity in the New England soil was i ndicated by a 50% PCB disappearance (gas chromatography), accumulation of chlorobenzoates (HPLC), and (CO2)-C-14 evolution from C-14-2CB. Th e PCB-degrading bacteria in the New England soil could be identified b y their positive hybridization to the bph gene probes, their ability t o produce the yellow meta-cleavage product from 2,3-dihydroxybiphenyl (2,3-DHB), and the degradation of specific PCB congeners by individual isolates in resting cell assays. Although the TVA capacitor bank soil lacked effective PCB-degrading populations, addition of a PCB-degradi ng organism and 10 000 p.p.m. biphenyl resulted in a >50% reduction of PCB levels. Molecular characterization of soil microbial populations in laboratory scale treatments is expected to be valuable in the desig n of process monitoring and performance verification approaches for fu ll scale bioremediation.