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 10<sup>2</sup> to 10<sup>9</sup> genes per liter of groundwater among the samples with VC reductive dehalogenase gene (<i>bvcA</i> and <i>vcrA</i>) abundances reaching 10<sup>8</sup> genes per liter of groundwater. Etheneotroph functional genes (<i>etnC</i> and <i>etnE</i>) and VC reductive dehalogenase genes (<i>bvcA</i> and <i>vcrA</i>) were strongly related to VC concentrations (<i>p</i> < 0.001). Methanotroph functional genes (<i>mmoX</i> and <i>pmoA</i>) were not related to VC concentration (<i>p</i> > 0.05). Samples from sites with bulk VC attenuation rates >0.08 year<sup>–1</sup> contained higher levels of etheneotroph and anaerobic VC-dechlorinator functional genes and transcripts than those with bulk VC attenuation rates <0.004 year<sup>–1</sup>. We conclude that both etheneotrophs and anaerobic VC-dechlorinators have the potential to simultaneously contribute to VC biodegradation at these sites.