Project description:The aim of this study is to obtain a systems level understanding of the interactions between Dehalococcoides and corrinoid-supplying microorganisms by analyzing community structures and functional compositions, activities and dynamics in trichloroethene (TCE)-dechlorinating enrichments. Metagenomes and metatranscriptomes of the dechlorinating enrichments with and without exogenous cobalamin were compared. Seven draft genomes were binned from the metagenomes. At an early stage (2 d), more transcripts of genes in the Veillonellaceae bin-genome were detected in the metatranscriptome of the enrichment with exogenous cobalamin compared to the one without cobalamin addition. Among these genes, sporulation-related genes exhibited the highest differential expression when cobalamin was not added, suggesting a possible release route of corrinoids from corrinoid-producers. Other differentially expressed genes include those involved in energy conservation and nutrient transport (including cobalt transport). The most highly expressed corrinoid de novo biosynthesis pathway was also assigned to the Veillonellaceae bin-genome. Targeted qPCR analyses confirmed higher transcript abundances of those corrinoid biosynthesis genes in the enrichment without exogenous cobalamin. Furthermore, Dehalococcoides' corrinoid salvaging and modification pathway was upregulated in response to the cobalamin stress. This study provides important insights into the microbial interactions and roles of members of dechlorinating communities under cobalamin-limited conditions.
Project description:Organohalide-respiring Dehalococcoidia bacteria are one of the few microorganisms capable of transforming chlorinated solvents to benign ethene in anoxic environments. The tceA gene found in these bacteria, coding the trichloroethene-dechlorinating RDase TceA, is frequently detected in contaminated groundwater but not recognized as a biomarker for vinyl chloride detoxification. Here, we demonstrate that the tceA-carrying Dehalococcoides mccartyi (Dhc) strains FL2 and 195 grow with VC as electron acceptor when sufficient vitamin B12 is provided. Global proteomic profiling confirmed the predominant TceA expression in VC-grown Dhc FL2 cells, providing a line of evidence for the implication of TceA in respiratory VC reductive dechlorination.
Project description:Dehalococcoides mccartyi strains are corrinoid-auxotrophic Bacteria and axenic cultures that require vitamin B12 (CN-Cbl) to conserve energy via organohalide respiration. Cultures of D. mccartyi strains BAV1, GT and FL2 grown with limiting amounts of 1 µg l(-1) CN-Cbl quickly depleted CN-Cbl, and reductive dechlorination of polychlorinated ethenes was incomplete leading to vinyl chloride (VC) accumulation. In contrast, the same cultures amended with 25 µg l(-1) CN-Cbl exhibited up to 2.3-fold higher dechlorination rates, 2.8-9.1-fold increased growth yields, and completely consumed growth-supporting chlorinated ethenes. To explore whether known cobamide-producing microbes supply Dehalococcoides with the required corrinoid cofactor, co-culture experiments were performed with the methanogen Methanosarcina barkeri strain Fusaro and two acetogens, Sporomusa ovata and Sporomusa sp. strain KB-1, as Dehalococcoides partner populations. During growth with H2/CO2, M. barkeri axenic cultures produced 4.2 ± 0.1 µg l(-1) extracellular cobamide (factor III), whereas the Sporomusa cultures produced phenolyl- and p-cresolyl-cobamides. Neither factor III nor the phenolic cobamides supported Dehalococcoides reductive dechlorination activity suggesting that M. barkeri and the Sporomusa sp. cannot fulfil Dehalococcoides' nutritional requirements. Dehalococcoides dechlorination activity and growth occurred in M. barkeri and Sporomusa sp. co-cultures amended with 10 µM 5',6'-dimethylbenzimidazole (DMB), indicating that a cobalamin is a preferred corrinoid cofactor of strains BAV1, GT and FL2 when grown with chlorinated ethenes as electron acceptors. Even though the methanogen and acetogen populations tested did not produce cobalamin, the addition of DMB enabled guided biosynthesis and generated a cobalamin that supported Dehalococcoides' activity and growth. Guided cobalamin biosynthesis may offer opportunities to sustain and enhance Dehalococcoides activity in contaminated subsurface environments.
Project description:Reductive dehalogenation mediated by organohalide-respiring bacteria plays a critical role in the global cycling of organohalides. Nonetheless, information on the dehalogenation enantioselectivity of organohalide-respiring bacteria remains limited. In this study, we report the enantioselective dechlorination of chiral polychlorinated biphenyls (PCBs) by Dehalococcoides mccartyi CG1. CG1 preferentially removed halogens from the (-)-enantiomers of the three major environmentally relevant chiral PCBs (PCB174, PCB149, and PCB132), and the enantiomer compositions of the dechlorination products depended on their parent organohalides. The in vitro assays with crude cell extracts or concentrated whole cells and the in vivo experiments with living cells showed similar enantioselectivities, in contrast with the distinct enantiomeric enrichment factors (εER) of the substrate chiral PCBs. Additionally, these results suggest that concentrated whole cells might be an alternative to crude cell extracts in in vitro tests of reductive dehalogenation activities. The enantioselective dechlorination of other chiral PCBs that we resolved via gas chromatography further confirmed the preference of CG1 for the (-)-enantiomers.IMPORTANCE A variety of agrochemicals and pharmaceuticals are chiral. Due to the enantioselectivity in biological processes, enantiomers of chiral compounds may have different environmental occurrences, fates, and ecotoxicologies. Many chiral organohalides exist in anaerobic or anoxic soils and sediments, and organohalide-respiring bacteria play a major role in the environmental attenuation and global cycling of these chiral organohalides. Therefore, it is important to investigate the dehalogenation enantioselectivity of organohalide-respiring bacteria. This study reports the discovery of enantioselective dechlorination of chiral PCBs by Dehalococcoides mccartyi CG1, which provides insights into the dehalogenation enantioselectivity of Dehalococcoides and may shed light on future PCB bioremediation efforts to prevent enantioselective biological side effects.