Sinorhizobium meliloti bluB Is Necessary for Production of 5,6-Dimethylbenzimidazole, the Lower Ligand of$B_{12}

An insight into a previously unknown step in$B_{12}$biosynthesis was unexpectedly obtained through our analysis of a mutant of the symbiotic nitrogen fixing bacterium Sinorhizobium meliloti. This mutant was identified based on its unusually bright fluorescence on plates containing the succinoglycan...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2006-03, Vol.103 (12), p.4634-4639
Main Authors: Campbell, Gordon R. O., Taga, Michiko E., Mistry, Kavita, Lloret, Javier, Anderson, Peter J., Roth, John R., Walker, Graham C.
Format: Article
Language:English
Subjects:
Alfalfa
Bacteria
Biosynthesis
Enzymes
Fluorescence
Ligands
Nodules
Phenotypes
Plants
Symbiosis
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Summary:An insight into a previously unknown step in$B_{12}$biosynthesis was unexpectedly obtained through our analysis of a mutant of the symbiotic nitrogen fixing bacterium Sinorhizobium meliloti. This mutant was identified based on its unusually bright fluorescence on plates containing the succinoglycan binding dye calcofluor. The mutant contains a Tn5 insertion in a gene that has not been characterized previously in S. meliloti. The closest known homolog is the bluB gene of Rhodobacter capsulatus, which is implicated in the biosynthesis of$B_{12}$(cobalamin). The S. meliloti bluB mutant is unable to grow in minimal media and fails to establish a symbiosis with alfalfa, and these defects can be rescued by the addition of vitamin$B_{12}$(cyanocobalamin) or the lower ligand of cobalamin, 5,6-dimethylbenzimidazole (DMB). Biochemical analysis demonstrated that the bluB mutant does not produce cobalamin unless DMB is supplied. Sequence comparison suggests that BluB is a member of the NADH/flavin mononucleotide (FMN)-dependent nitroreductase family, and we propose that it is involved in the conversion of FMN to DMB.
ISSN:0027-8424