Prevalence, activity and diversity of vinyl chloride oxidizing bacteria at contaminated sites

Vinyl chloride (VC), a known human carcinogen, commonly accumulates during anaerobic reductive dechlorination of the more chlorinated ethenes in contaminated groundwater plumes. There are a variety of aerobic bacteria that can fortuitously oxidize (i.e. co-metabolize) VC in groundwater in the presence of other compounds (e.g. methanotrophs).  A potentially important group of VC-oxidizers are the ethene-assimilators (i.e. “etheneotrophs”).  These obligate aerobes are capable of co-metabolizing VC in the presence of ethene, and can also adapt to VC as a growth substrate (i.e. become VC-assimilators). Etheneotroph functional genes key to VC and ethene biodegradation are etnC, which encodes the alkene monooxygenase (AkMO) alpha subunit and etnE, which encodes the epoxyalkane:coenzyme M transferase (EaCoMT). In recent efforts, we have developed a quantitative, real-time PCR (qPCR) method that targets these key functional genes (and their transcripts via reverse transcription (RT)-qPCR).  We are also exploring the diversity of VC-assimilators (and associated EtnE genes) in a VC-oxidizing laboratory culture derived from contaminated site groundwater using stable isotope probing (SIP) techniques.  Application of etheneotroph qPCR to DNA from several VC-contaminated sites confirmed etheneotroph presence (etnC/etnE abundance ~10³-10⁵ genes/L of groundwater).  Evidence of etnC/etnE expression in selected groundwater samples was obtained via RT-qPCR.  SIP experiments revealed that VC-assimilator diversity in this culture is potentially greater than represented in pure culture and that microbes harboring etnE participate in VC-assimilation. Continued application of these methods to additional sites is expected to shed new light on the prevalence, diversity and activity of VC-oxidizing etheneotrophs in contaminated groundwater environments.