Sustained Aerobic Degradation of Trichloroethylene by Ammonia-Oxidizing Bacteria Naturally Associated with Wetland Plant Roots

Abstract

Bench-scale microcosms with wetland plant roots in aerobic growth media were used to characterize the microbial contributions to contaminant degradation during aerobic cometabolism of trichloroethylene (TCE) with ammonium. Aqueous growth media, ammonium, and TCE were replaced weekly in batch microcosms while retaining roots and root- associated biomass. Genetic results indicated that ammonium-oxidizing bacteria (AOB) can be enriched from wetland plant roots while analysis of contaminant and oxygen concentrations showed that those microorganisms can degrade TCE by aerobic cometabolism. Cometabolism of TCE, at 43 µg/L, was sustainable over the course of 9 weeks, with an ammonium concentration of 30 mg/L as nitrogen. However, at 64 µg/L of TCE, ammonium oxidation and TCE cometabolism were completely inhibited in two weeks. This indicated that at some point between 43 and 64 µg/L of TCE with ammonium at 30 mg/L as nitrogen there is a threshold. Cometabolism- induced inhibition of ammonium and TCE degradation did not equate to a lower abundance of the amoA gene in the microcosms, implying that the capacity to recover from TCE inhibition was still intact, given time and removal of TCE stress.