Recovery of microbially mediated processes in soil augmented with a pentachlorophenol-mineralizing bacterium

Specific physiological groups can be used to evaluate the recovery of soil microbial communities following disturbance. In this study, soil was contaminated with pentachlorophenol (PCP) to assess the resiliency of microorganisms responsible for carbon and nitrogen cycling. Methane fluxes were monitored in soil microcosms to evaluate the effects of contamination and augmentation on microbial populations involved in carbon cycling. The addition of a PCP-mineralizing bacterium, Sphingomonas chlorophenolica strain RA2, enhanced the recovery of methane-oxidizing capacity relative to uninoculated treatments when soil was contaminated with low concentrations of PCP (10 and 50 microg/g soil, ppm). At the highest level of PCP contamination tested (300 ppm), there was no recovery of methane-oxidizing capacity whether or not the PCP-mineralizing bacterium was added to soil. The nitrogen-cycling capacity of contaminated and augmented soil was tested by measuring nitrification potentials. The addition of PCP resulted in a concentration-dependent reduction in nitrification rates. After three months of incubation, all augmented soils had nitrification rates equivalent to the uncontaminated control, and the uninoculated soils contaminated with 100 and 300 ppm PCP still were impaired in their nitrification potentials. These results indicate that biological removal of a contaminant has the potential to restore microbially mediated processes to levels observed prior to contamination.