Temporal abundance and activity trends of vinyl chloride (VC)-degrading bacteria in a dilute VC plume at Naval Air Station Oceana.

Assessment and monitoring of microbial community dynamics is useful when tracking the progress of vinyl chloride (VC) bioremediation strategies, particularly in dilute plumes where apparent VC attenuation rates are low. In a long-term field study, the abundance and the activity of microbial VC degraders were tracked in three monitoring wells (MW05, MW25, and MW19) along a dilute VC plume at Naval Air Station (NAS) Oceana. High-throughput sequencing of partial 16S ribosomal RNA (rRNA) genes and transcripts revealed diverse groundwater microbial communities and showed that methanotrophs and anaerobic respirers (e.g., methanogens, sulfate reducers, and iron reducers) were among the most active and abundant guilds. Quantitative PCR analysis showed that among bacterial guilds with a potential to contribute to VC biodegradation, methanotrophs were the most abundant and active microbial group. Ethene-oxidizing bacterial populations were less abundant and relatively inactive compared to methanotrophs. In MW19, expression of functional genes associated with both aerobic VC oxidation and anaerobic VC reduction was observed. Overall, our results reveal that the groundwater community contains various active bacterial guilds previously associated with metabolic and cometabolic VC degradation processes either under aerobic and anaerobic conditions that might have contributed to the slowly decreasing VC concentrations at the NAS Oceana site over the 6-year study period.