Sustainable Growth of Dehalococcoides mccartyi 195 by Corrinoid Salvaging and Remodeling in Defined Lactate-Fermenting Consortia

Abstract

dCorrinoids are essential cofactors of reductive dehalogenases in Dehalococcoides mccartyi, an important bacterium in bioremediation, yet sequenced D. mccartyi strains do not possess the complete pathway for de novo corrinoid biosynthesis. Pelosinus sp. and Desulfovibrio sp. have been detected in dechlorinating communities enriched from contaminated groundwater without exogenous cobalamin corrinoid. To investigate the corrinoid-related interactions among key members of these communities, we constructed consortia by growing D. mccartyi strain 195 (Dhc195) in cobalamin-free, trichloroethene (TCE)-and lactateamended medium in cocultures with Desulfovibrio vulgaris Hildenborough (DvH) or Pelosinus fermentans R7 (PfR7) and with both in tricultures. Only the triculture exhibited sustainable dechlorination and cell growth when a physiological level of 5,6-dimethylbenzimidazole (DMB), the lower ligand of cobalamin, was provided. In the triculture, DvH provided hydrogen while PfR7 provided corrinoids to Dhc195, and the initiation of dechlorination and Dhc195 cell growth was highly dependent on the growth of PfR7. Corrinoid analysis indicated that Dhc195 imported and remodeled the phenolic corrinoids produced by PfR7 into cobalamin in the presence of DMB. Transcriptomic analyses of Dhc195 showed the induction of the CbiZ-dependent corrinoid-remodeling pathway and BtuFCD corrinoid ABC transporter genes during corrinoid salvaging and remodeling. In contrast, another operon annotated to encode a putative iron/cobalamin ABC transporter (DET1174-DET1176) was induced when cobalamin was exogenously provided. Interestingly, a global upregulation of phage-related genes was observed when PfR7 was present. These findings provide insights into both the gene regulation of corrinoid salvaging and remodeling in Dhc195 when it is grown without exogenous cobalamin and microbe-to-microbe interactions in dechlorinating microbial communities.C hlorinated solvents such as tetra-and trichloroethene (PCE/ TCE) have been among the most common subsurface contaminants in the United States for decades (1, 2). In situ bioremediation is an effective, economical, and environmentally friendly technology for treating chlorinated solvents (2, 3). Dehalococcoides mccartyi is the only known bacterium capable of carrying out respiratory reductive dechlorination of chloroethenes to nontoxic ethene and plays a key role in the bioremediation of contaminated groundwater (4, 5).As cofactors of reductive dehalogenases (RDases), the enzymes responsible for reductive dechlorination, corrinoids (e.g., cobalamin) are essential nutrients for supporting D. mccartyi growth and dechlorination. Genomic analyses of sequenced D. mccartyi strains reveal a lack of complete corrinoid biosynthesis pathways, rendering D. mccartyi incapable of synthesizing corrinoids de novo (6, 7). Exogenous cobalamin (a specific corrinoid also known as vitamin B 12 ) is generally added to grow D. mccartyi in isolation (8). Cobalamin, 5-methylbenzimidazolylcobamide ([5-MeBza]Cba), and 5-methoxyb...

Efficient Metabolic Exchange and Electron Transfer within a Syntrophic Trichloroethene-Degrading Coculture of Dehalococcoides mccartyi 195 and Syntrophomonas wolfei

“…However, the mechanisms that regulate the activity of D. mccartyi within natural ecosystems and shape its functional robustness in disturbed environments are poorly understood due to multiscale microbial community complexity and heterogeneity of biogeochemical processes involved in the sequential degradation (3,4). D. mccartyi exhibits specific restrictive metabolic requirements for a variety of exogenous compounds, such as hydrogen, acetate, corrinoids, biotin, and thiamine, which can be supplied by other microbial genera through a complex metabolic network (1,(5)(6)(7)(8). Therefore, the growth of D. mccartyi is more robust within functionally diverse microbial communities that are deterministically assembled than in pure cultures (5,8,9).…”

Ecophysiology and environmental distribution of organohalide-respiring bacteria

“…However, to our knowledge, these taxa are not known to provide the more important organic cofactors such as vitamin B12 needed by Dcm, hence they are not likely "sufficient" as companions to sustain Dcm growth. In line with this, other studies showed the importance of particular syntrophic partners belonging to Firmicutes and Deltaproteobacteria in providing the "right" cobamide lower base of vitamin B12 that is vital for Dcm dechlorination [95,300] but cannot be provided even by closely related microbes [93,299].…”

“…The most dynamic period was after day 72 during which the average  Table S6.6) is likely due to their glycerol fermentation capacity [408][409][410][411]. Moreover, Pelosinus strains were shown to sustain growth of Dcm by providing the necessary corrinoids [95,300].…”

Algal–bacterial synergy in treatment of winery wastewater

“…With regard to cobalamin, bacteria in consortia are known to remodel corrinoids obtained from other species, 37 however, studies on algae are limited. One recent study has shown that some eukaryotic algae can convert pseudocobalamin into cobalamin when provided with 5,6-dimethylbenzimidazole.…”