Survey of one-carbon metabolism in Desulfitobacteria

Desulfitobacterium is a Gram-positive obligate anaerobic bacterium affiliated to the Firmicutes with a highly versatile carbon and energy metabolism. Increasing interest in this genus came with its involvement in the degradation of chlorinated compounds used as terminal electron acceptor in a process called dehalorespiration. A proteomic study in our laboratory revealed the participation of the Wood-Ljungdahl pathway in tetrachloroethene dehalorespiration when D. hafniense strain TCE1 was cultivated in presence of hydrogen and carbon dioxide, providing first indication for CO2 fixation in Desulfitobacterium. A genomic survey of both Desulfitobacterium available genomes (D. hafniense strain Y51 and strain DCB-2) showed a full set of genes involved in carbon dioxide and carbon monoxide metabolism similarly to the five CODH complexes present in the thermophilic CO-utilizing bacterium Carboxydothermus hydrogenoformans (Wu et al., 2006, PloS Genetics 1:e65), including CODH-III complex which has been shown to participate to acetogenesis in Moorella thermoacetica (Pierce et al., 2008, Environ. Microbiol. 10:2550). No clear evidence however has been yet given for acetogenesis or hydrogenogenesis in Desulfitobacterium. A survey of B12 metabolism in Desulfitobacterium revealed the presence of 15 and 23 predicted B12-dependent methyltransferases (MeTr) in the genome of strains Y51 and DCB-2, respectively. A detail study of the genetic environment of the MeTr suggests that most of them are part of O-demethylase complexes. Phenyl methyl ethers have been indeed shown to serve as electron donor for some Desulfitobacterium strains (Kreher et al., 2008, Arch. Microbiol. 190:489). A few other MeTr belong to predicted archaeal-type di- and trimethylamine methyltransferases complexes, one of which being a putative pyrrolysine containing enzyme. The richness and functional redundancy of Desulfitobacteria make them good candidates to further study specific pathways dedicated to one-carbon metabolism.