Bacterial community changes in TCE biodegradation detected in microcosm experiments

Laboratory microcosm experiments were set up to model biodegradation of trichloroethylene (TCE). Groundwater samples from two contaminated sites were taken, one of them with low (70 mg L⁻¹), the other with high sulfate (685 mg L⁻¹) concentration. In order to assess the biodegradative potential of natural microbiota, supplementary substrates (whey or molasses) were added to the bottles. At day 54, 98, 155, and 318, chemical and bacteriological parameters (i.e., Dehalococcoides test) were investigated. Terminal restriction fragment length polymorphism (T-RFLP) based diversity assessments were carried out to observe the bacterial community changes. Whey and molasses enhanced degradation at different rates. In the case of samples with high sulfate content and amended with whey, no ethylene, ethane, or methane was generated. Both ethylene and methane production was detected in samples of low sulfate content with added whey. The results of Dehalococcoides tests were positive for all control and amended samples. Based on T-RFLP analysis, the bacterial communities of high sulfate concentration groundwater microcosms amended with molasses or whey were very similar, while the communities of groundwater samples with low sulfate concentration were different when supplemented with whey or molasses. The rRNA and rDNA based investigations suggest that the proportions of the active microbes and the microbes present in the microcosms differ.