Bioremediation of trichloroethylene by indigenous microbes in groundwater

Abstract

Trichloroethylene (TCE) is a widespread contaminant of groundwater, which potentially can be degraded by indigenous microbes. Degradation can be augmented with the use of cometabolites, which stimulate bacteria to produce the enzymes essential to TCE degradation. Groundwater contaminated with TCE was received from a U.S. Department of Energy site in Ohio to test for potential bioremediation of TCE by indigenous mircobes. Groundwater treatments, augmented with various potential cometabolites including CompoundC and phenol, were spiked with 14C-TCE and the amount 14CO2 produced was analyzed to determine rates of TCE degradation.

Culture conditions were manipulated by supplying nutrients and reducing equivalents and treatments were optimized to produce maximal TCE degradation. Under optimized conditions CompoundC did not support increased TCE mineralization at this site. An optimized phenol treatment supported 14% mineralization within seven days.

Molecular techniques including RFLP and DNA sequencing of 16S rDNA were used to assess the microbial community structure of the three treatments, unamended groundwater, groundwater amended with phenol (Phenol Culture), and phenol culture after incubation with site concentrations of TCE (Phenol Culture + TCE), respectively. Phylogenetic trees were used to determine the evolutionary relationship between dominant species in each treatment and illustrate the shift in microbial community structure as a result of augmentation. The indigenous groundwater community was slightly more diverse than the augmented treatment communities. The clones extracted from the augmented communities related most closely with ß -proteobacteria. One common RFLP pattern was observed to predominate in each of the three treatments. DNA sequencing revealed this predominant pattern to be closely related to "Variovorax" a ß-proteobacteria. With the exception of this one common pattern, RFLPs were unique within the treatment groups. This study demonstrated that augmentation with phenol substantially increased TCE degradation as well as altered the community structure of indigenous bacteria in groundwater. The augmented phenol community was identified to support bacterial including "Variovorax," "Pseudomonas," and "Burkholderia," which have previously been identified to be capable of degrading TCE.