FACTORS AFFECTING THE ENHANCEMENT OF PCB DEGRADATIVE ABILITY OF SOIL MICROBIAL-POPULATIONS

In this study, we compared the capacity of freshly isolated microbial populations obtained from soils with a history of contamination and ev aluated the effect of analog enrichment on the potential of PCB degrad ation attained by the enhanced populations. It has previously been sug gested that PCB degrading ability should improve through mutations of the oxygenase that can increase reactivity of the enzyme towards vario us individual congeners. Our results show that the chlorine content of the PCB mixture and duration of soil contamination (number of years) have no effect on the natural evolution of the ability of soil microbi al populations to degrade higher chlorinated PCBs. Moreover, although our results provided evidence that analog enrichment can favor the sel ection of oxygenases with increased activities, we failed to select fo r populations that are able to degrade higher chlorinated PCBs more ef ficiently. Our data also clearly showed that chlorobenzoates, the end- products of the chlorobiphenyl degradation pathway (or their metabolit es) interfere with PCB degradation. Therefore, the efficiency of PCB d egradation is not only impaired by the substrate selectivity pattern o f the chlorobiphenyl oxygenases, but also by the stringent control of metabolite production and it is likely that population adjustment to p revent production of metabolites that could interfere with PCB degrada tion would be difficult to achieve through natural selection.