Trichloromethane dechlorination by a novel Dehalobacter sp. strain 8M reveals a third contrasting C and Cl isotope fractionation pattern within this genus

Trichloromethane (TCM) is a pollutant frequently detected in contaminated aquifers, and only four bacterial strains are known to respire it. Here, we obtained a novel Dehalobacter strain capable of transforming TCM to dichloromethane, which was denominated Dehalobacter sp. strain 8M. Besides TCM, strain 8M also completely transformed 1,1,2-trichloroethane to vinyl chloride and 1,2-dichloroethane. Quantitative PCR analysis for the 16S rRNA genes confirmed growth of Dehalobacter with TCM and 1,1,2-trichloroethane as electron acceptors. Carbon and chlorine isotope fractionation during TCM transformation was studied in cultured cells and in enzymatic assays with cell suspensions and crude protein extracts. TCM transformation in the three studied systems resulted in small but significant carbon (epsilon(C) = -2.7 +/- 0.1 parts per thousand for respiring cells, -3.1 +/- 0.1 parts per thousand for cell suspensions, and - 4.1 +/- 0.5 parts per thousand for crude protein extracts) and chlorine (epsilon(Cl) = -0.9 +/- 0.1 parts per thousand, -1.1 +/- 0.1 parts per thousand, and - 1.2 +/- 0.2 parts per thousand, respectively) isotope fractionation. A characteristic and consistent dual CCl isotope fractionation pattern was observed for the three systems (combined Lambda(C/Cl) = 2.8 +/- 0.3). This Lambda(C/Cl) differed significantly from previously reported values for anaerobic dechlorination of TCM by the corrinoid cofactor vitamin B12 and other Dehalobacter strains. These findings widen our knowledge on the existence of different enzyme binding mechanisms underlying TCM-dechlorination within the genus Dehalobacter and demonstrates that dual isotope analysis could be a feasible tool to differentiate TCM degraders at field studies.

Automated summary

A novel Dehalobacter strain capable of transforming TCM to dichloromethane was obtained, along with its ability to transform other chlorinated compounds. Analysis of 16S rRNA genes confirmed growth of Dehalobacter with TCM and other chlorinated compounds as electron acceptors, and isotope fractionation during the transformation process was studied. These findings demonstrate a potential tool for differentiating TCM degraders in field studies.