Relationships between the Abundance and Expression of Functional Genes from Vinyl Chloride (VC)-Degrading Bacteria and Geochemical Parameters at VC-Contaminated Sites

Bioremediation of vinyl chloride (VC) contamination in groundwater could be mediated by three major bacterial guilds: anaerobic VC-dechlorinators, methanotrophs, and ethene-oxidizing bacteria (etheneotrophs) via metabolic or cometabolic pathways. We collected 95 groundwater samples across 6 chlorinated ethene-contaminated sites and searched for relationships among VC biodegradation gene abundance and expression and site geochemical parameters (e.g., VC concentrations). Functional genes from the three major VC degrading bacterial guilds were present in 99% and expressed in 59% of the samples. Etheneotroph and methanotroph functional gene abundances ranged from 102 to 109 genes per liter of groundwater among the samples with VC reductive dehalogenase gene (bvcA and vcrA) abundances reaching 108 genes per liter of groundwater. Etheneotroph functional genes (etnC and etnE) and VC reductive dehalogenase genes (bvcA and vcrA) were strongly related to VC concentrations (p < 0.001). Methanotroph functional genes (mmoX and pmoA) were not related to VC concentration (p > 0.05). Samples from sites with bulk VC attenuation rates >0.08 year(-1) contained higher levels of etheneotroph and anaerobic VC-dechlorinator functional genes and transcripts than those with bulk VC attenuation rates <0.004 year We conclude that both etheneotrophs and anaerobic VC-dechlorinators have the potential to simultaneously contribute to VC biodegradation at these sites.