Regulation of the Corrinoid Metabolism in Desulfitobacteria

The corrinoid cofactor is essential to organohalide respiration (OHR) as key element in virtually all reductive dehalogenases. Desulfitobacteria, and more particularly D. hafniense, represent a group of versatile OHR bacteria able to produce corrinoids de novo, as initially discovered in the genome of D. hafniense Y51 (1). Since then several desulfitobacteria genomes have been sequenced revealing that the corrinoid metabolism (biosynthesis, transport, regulation) represents a conserved trait in a highly variable genetic background in the members of this genus. A thorough analysis of corrinoid-related genes in the genomes of D. hafniense strains Y51, DCB-2 (2) and TCE1 (3) revealed the presence of eighteen distinct cobalamin riboswitches (Cbl-RS). Cbl-RS structures are known to regulate the transcription or translation of downstream located genes by corrinoid-dependent conformational changes occurring in the 5’-untranslated region of the corresponding RNA transcripts. In vitro in-line probing analysis of three significantly different riboswitches of D. hafniense TCE1 highlighted their role as regulatory elements in the corrinoid metabolism. In vivo analysis of the transcription of the directly downstream genes upon addition of various corrinoids clearly confirmed it (4). Furthermore, we successfully cultivated D. hafniense TCE1 in the complete absence of corrinoid in the medium, and preliminary HPLC analysis suggested that strain TCE1 produces several types of corrinoids. The corrinoid metabolism of desulfitobacteria have made them excellent candidates for acquiring OHR metabolism (5), while their wide distribution in OHR ecological niches suggests that this genus might be an important source of corrinoids for members of the genera Dehalococcoides and Dehalobacter. (1) Nonaka et al. (2006), J Bacteriol 188:2262. (2) Kim et al. (2012), BMC Microbiol 8:12. (3) JGI Project ID 403245, coordinated by H. Smidt (Wageningen University). (4) Choudhary et al. (2013), J Bacteriol 195:5186. (5) Duret et al. (2012), Appl Environ Microbiol 78:6121.