Guided cobalamin biosynthesis supports Dehalococcoides mccartyi reductive dechlorination activity

Abstract

Dehalococcoides mccartyi strains are corrinoid-auxotrophic Bacteria and axenic cultures that require vitamin B 12 (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 H 2 /CO 2 , 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.

Diversity of Cobalamin Riboswitches in the Corrinoid-Producing Organohalide Respirer Desulfitobacterium hafniense

“…Confronting this knowledge with the well-characterized corrinoid anaerobic biosynthetic pathway (1), we re-annotated the full pathway and extended it to include the genomes of D. hafniense strains DCB-2 and TCE1, thus suggesting that D. hafniense, in contrast to Dehalococcoides mccartyi, is a versatile and corrinoidprototroph OHR bacterium. It would be interesting to test whether Desulfitobacterium-Dehalococcoides cocultures such as those obtained previously (57) would allow the latter to fully dechlorinate tetrachloroethene (PCE) without corrinoid addition in the medium, as was shown in recent studies with Geobacter and other corrinoid-producing bacteria (58,59). Other OHR bacteria such as Sulfurospirillum multivorans (13), Geobacter lovleyi (60), and Dehalobacter restrictus (61) display a large variety of relationships to corrinoid biosynthesis, further emphasizing the importance of studying individual model organisms.…”

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

“…Although dechlorinating microbial communities have been extensively studied over the past decades (4, 10, 12, 13), community assembly processes in the highly specialized ecological niche of Dehalococcoides and the network of interactions between D. mccartyi, its syntrophic partners and other coexisting community members have yet to be deciphered. The optimization of D. mccartyi-based bioremediation systems to treat TCE-contaminated groundwater would be facilitated by a system-level understanding of interspecies electron, energy and metabolite transfers that shape the structural and functional robustness of TCE-dechlorinating microbial communities.To date, only a few studies of D. mccartyi-containing constructed cocultures and tricultures have been published (5,7,(14)(15)(16). A study with D. mccartyi 195 (strain 195) revealed that its growth in defined medium could be optimized by providing high concentrations of vitamin B 12 and that, over the short term, the strain could be grown to higher densities in cocultures and tricul- …”

“…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).…”

“…To date, only a few studies of D. mccartyi-containing constructed cocultures and tricultures have been published (5,7,(14)(15)(16). A study with D. mccartyi 195 (strain 195) revealed that its growth in defined medium could be optimized by providing high concentrations of vitamin B 12 and that, over the short term, the strain could be grown to higher densities in cocultures and tricul-tures with the fermenters Desulfovibrio desulfuricans and/or Acetobacterium woodii that convert lactate to generate the hydrogen and acetate required by D. mccartyi (5).…”

“…A study with D. mccartyi 195 (strain 195) revealed that its growth in defined medium could be optimized by providing high concentrations of vitamin B 12 and that, over the short term, the strain could be grown to higher densities in cocultures and tricul-tures with the fermenters Desulfovibrio desulfuricans and/or Acetobacterium woodii that convert lactate to generate the hydrogen and acetate required by D. mccartyi (5). Recent studies demonstrated interspecies corrinoid transfer between Geobacter lovleyi and D. mccartyi strains BAV1 and FL2 (16) and interspecies cobamide transfer from a corrinoid-producing methanogen and acetogen to D. mccartyi (7). Another study showed that strain 195 can grow in a long-term sustainable syntrophic association with Desulfovibrio vulgaris Hildenborough (DvH) as a coculture, as well as with hydrogenotrophic methanogen Methanobacterium congolense (MC) as a triculture (15).…”