Effect of trichloroethylene and tetrachloroethylene on methane oxidation and community structure of methanotrophic consortium

The methane oxidation rate and community structure of a methanotrophic consortium were analyzed to determine the effects of trichloroethylene (TCE) and tetrachloroethylene (PCE) on methane oxidation. The maximum methane oxidation rate^(Vmax) of the consortium was 326.8 μmol·g-dry biomass^-1·h^-1, and it had a half-saturation constant^(Km) of 143.8 μM. The addition of TCE or PCE resulted in decreased methane oxidation rates, which were decreased from 101.73 to 5.47-24.64 μmol·g-dry biomass^-1·h^-1 with an increase in the TCE-to-methane ratio, and to 61.95-67.43 μmol·g-dry biomass^-1·h^-1 with an increase in the PCE-to-methane ratio. TCE and PCE were non-competitive inhibitors for methane oxidation, and their inhibition constants^(Ki) were 33.4 and 132.0 μM, respectively. When the methanotrophic community was analyzed based on pmoA using quantitative real-time PCR (qRT-PCR), the pmoA gene copy numbers were shown to decrease from 7.3 ± 0.7 × 10⁸ to 2.1-5.0 × 10⁷ pmoA gene copy number · g-dry biomass^-1 with an increase in the TCE-to-methane ratio and to 2.5-7.0 × 10 ⁷ pmoA gene copy number · g-dry biomass^-1 with an increase in the PCE-to-methane ratio. Community analysis by microarray demonstrated that Methylocystis (type II methanotrophs) were the most abundant in the methanotrophic community composition in the presence of TCE. These results suggest that toxic effects caused by TCE and PCE change not only methane oxidation rates but also the community structure of the methanotrophic consortium.