Chloroform is common groundwater priority pollutant ranked 11th on the US-EPA's list of hazardous chemicals. Chloroform is a naturally occurring compound however; human activity has introduced chloroform en masse into subsurface environments. For example in the USA around 25% of the priority polluted sites are chloroform impacted. Additionally, chloroform is problematic in that it is a powerful inhibitor of most subsurface microbial processes including organohalide respiration. Therefore, where chloroform exists as a co-pollutant with other organohalides, such as chlorinated ethanes and ethenes, bioremediation typically is not possible.
Given the problematic nature of chloroform in anoxic environments, one of our research objectives has been to discover and understand chloroform-degrading bacteria. Using sub-surface sediment (5 m) derived from an organohalide impacted site near Botany Bay Sydney, a novel chloroform respiring bacterium from the genus Dehalobacter was discovered, isolated, biochemically characterized and named Dehalobacter sp strain UNSWDHB. Strain UNSWDHB can tolerate up to 500 mg l-1 of chloroform and dechlorinate it to dichloromethane at a maximal rate of 12 mg l -1 day-1. The reductive dehalogenase (TmrA) was functionally characterized and shown to dechlorinate a range of chlorinated ethanes in addition to chloroform. Additionally isotope ratio mass spectrometry was used to characterize the isotope ratio fingerprint associated with chloroform respiration by strain UNSWDHB. This is a powerful technique for determining in situ activity of microorganisms.
The discovery of this organism has the potential to alleviate the inhibitory effect of chloroform where it exists as a co-pollutant. This can therefore open up many organohalide polluted sites for cleanup by bioremediation.