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

Abstract

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 2 to 10 9 genes per liter of groundwater among the samples with VC reductive dehalogenase gene ( bvcA and vcrA ) abundances reaching 10 8 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 –1 . We conclude that both etheneotrophs and anaerobic VC-dechlorinators have the potential to simultaneously contribute to VC biodegradation at these sites.