Organochlorine contaminated groundwater represents a major environmental concern globally. Chlorinated ethenes, ethanes and methanes are variously toxic and carcinogenic dense, semi-volatile and sparingly soluble solvents that have seen widespread use and subsequent environmental contamination. Biological remediation of anaerobic groundwater contaminated with these solvents involves organohalide respiring bacteria (ORB) using them as electron acceptors.
To facilitate site remediation in Australia we have developed three enrichment cultures for reduction of chlorinated ethenes, ethanes and methanes to innocuous end products. The chlorinated ethene degrading culture predominantly consists of Dehalococcoides species carrying the vcrA gene for vinyl chloride reduction to ethene. Dehalobacter and Geobacter species are also present and responsible for reduction of perchloroethene to trichloroethene and trichloroethene to cis-1,2-dichloroethene. The chlorinated ethane degrading enrichment ultimately generated a pure culture Desulfitobacterium lineage able to utilise ethanol as a carbon and energy source and tolerate high solvent concentrations and low pH, in keeping with the site from which it was derived.
The chlorinated methane degrading culture obtained is the first culture known to completely detoxify chloroform1 . The first step in the process is chloroform reduction to dichloromethane and the second step is fermentation of dichloromethane to acetate, hydrogen and carbon dioxide. Both steps are carried out by a Dehalobacter lineage. The ability to grow Dehalobacter on dichloromethane is the first demonstration that this genus is not strictly obligate with respect to organohalide respiration. Syntrophic homoacetogenic bacteria (Acetobacterium) and methanogenic archaea (Methanoculleus) are also present in the culture. The culture is tolerant to and rapidly degrades high concentrations of chloroform.