Isolation and characterization of chloroform, 1,1,2-trichloroethane and dichloromethane degrading bacteria.

摘要

Groundwater is a vital source of water for drinking and daily usage throughout the world including Australia. The improper disposal of chlorinated compounds such as chloroform 3, 1,1,2-trichloroethane (1,1,2-TCA) and dichloromethane (DCM) has led to widespread soil and groundwater pollution that has given rise to environmental and health concerns. Thus, the remediation of these compounds is a priority. The use of bacteria for remediation or bioremediation has been found to be more cost efficient and sustainable than alternative mechanisms. The discovery and understanding of bacteria with the ability to detoxify these compounds is essential for the success of bioremediation applications. Hence, there is a need for isolation and characterization of these unique bacteria. CF and 1,1,2-TCA are prevalent in the environment but only a very limited number of bacteria with the ability to detoxify them have been identified. The aim of this study was to isolate and characterize the bacterium that was responsible for reductive dechlorination of CF to DCM from a previously described CF respiring enrichment culture. Results describe the isolation of a novel CF respiring bacterium belonging to the Firmicutes phylum designated, Dehalobacter sp. UNSWDHB. Phylogenetic studies indicated that strain UNSWDHB was more closely related to Dehalobacter sp. CF and DCA compared to Dehalobacter restrictus PER-K23. Characterization studies revealed that UNSWDHB is also capable of transforming 1,1,2-TCA to 1,2-DCA and VC, tolerate up to 3.35 mM of CF and 1 mM of soluble sulfide. The sequencing, annotation and analysis of the genome of this novel isolate revealed that strain UNSWDHB harbours genes encoding 19 putative reductive dehalogenases. Furthermore, results indicated that UNSWDHB has a complete set of genes involving de novo corrinoid biosynthesis, nitrogen fixation, menaquinone biosynthesis, Wood Ljungdahl pathway, chemotaxis and motility. UNSWDHB was found to have genes encoding for 9 hydrogenases. Results from blue native polyacrylamide gel electrophoresis together with shotgun proteomics identified the reductive dehalogenase responsible for transformation of CF and 1,1,2-TCA. This study also aimed to isolate and characterize the bacterium responsible for transformation of DCM from a previously described DCM fermenting enrichment. The isolation of a novel Gram negative bacterium belonging to the Peptococcaceae family is reported and designated, DCMF. Phylogenetic studies showed that it is most closely related to Dehalobacterium formicoaceticum. Functional characterization revealed that DCMF is a DCM fermenting homoacetogen. Results from this study and the cultures generated have implications relevant to the anaerobic biological remediation of sites contaminated with CF, 1,1,2-TCA and/or DCM.