| A polychlorinated biphenyl (PCB) bioaugmentation approach has been developed that uses PCB-degrading bacteria repeatedly applied to contaminated soil along with an inducing substrate, carvone, and a surfactant, sorbitan trioleate. Recently, earthworms and plants were incorporated into the system to enhance vertical movement of the inoculated bacteria and to promote PCB degradation below the soil surface. However, the application and optimization of this approach as a treatment technology requires the demonstration of its effectiveness, reliability and predictability, as well as better understanding of the biodegradation process. The aim of this research was to provide evidence for the efficacy of the PCB bioaugmentation approach through the analysis of soil bacterial communities. The analysis consisted of monitoring the inoculated bacteria using bph gene specific primers, measurement of biphenyl utilizer population density and microbial metabolic activity, and characterization of community DNA fingerprints during bioaugmentation.; Results from soil microcosm studies indicated that bioaugmentation amendments increased the number of biphenyl utilizers and microbial activity, selected for fast growing bacteria, and shifted bacterial communities structures in the soil. However, high concentrations of PCBs and chlorobenzoates inhibited microbial metabolic activity and consequently inhibited degradation. Further studies using 20-cm soil columns, showed that incorporation of plants or earthworms into the bioaugmentation treatment accelerated PCB degradation within the top 9 cm of the columns. The results suggested that the inoculated bacteria provided necessary enzymes involved in the transformation of PCBs to their intermediates; whereas, plants or earthworms enhanced dispersal of PCB degraders in the columns, and promoted degradation of PCB intermediates by increasing indigenous bacterial activity and enrichment of indigenous degrader populations. The acquired knowledge will be used for future improvement and evaluation of PCB remediation techniques, and provides a general strategy to monitor microbial communities during bioremediation of soil contaminants. |
