Effects of trichloroethylene on community structure and activity of methanotrophs in landfill cover soils

•Methylocaldum and Methylobacter dominated in waste biocover soil (WBS).•Type II methanotrophs Methylocystis dominated in landfill cover soils (LCS).•Methylobacter seemed tolerant to TCE and/or may play a key role in TCE degradation.•A high CH4 oxidation activity and a high TCE degradation rate occurred in WBS.•The abundance of pmoA in WBS was two orders of magnitudes higher than in LCS.

Landfill cover soil (LCS) plays an important role in mitigating the emission of CH4 and volatile organic gases from landfills to the atmosphere. In this study, effect of trichloroethylene (TCE) on community structure and activity of methanotrophs, as well as TCE degradation efficiency was investigated in waste biocover soil (WBS), which was collected from a landfill bioreactor treating organic waste, in comparison with LCS. The CH4 oxidation activity and TCE degradation rate were higher in WBS compared to those in LCS. The TCE degradation rates in both soils were enhanced with the increase of TCE concentration within 50 ppmv. Compared to LCS, the TCE inhibitory concentration that caused inhibition of CH4 oxidation activity was greater for WBS. The abundance of mmoX was similar in both soils during the whole experiment, while the average abundance of pmoA in WBS was about two orders of magnitudes higher than in LCS. Type I methanotrophs (Methylocaldum, Methylomonas, Methylosarcina and Methylobacter) and type II methanotrophs (Methylocystis) were abundant in both soils. Among them, type I methanotrophs Methylocaldum and Methylobacter dominated in WBS, while type II methanotrophs Methylocystis predominated in LCS. The relative abundance of Methylobacter increased with an increase of TCE concentration and exposure time in both soils, especially in WBS, indicating that Methylobacter seemed tolerant to TCE and/or may play an important role in the TCE degradation.