Sinorhizobium meliloti bluB is necessary for production of 5,6-dimethylbenzimidazole, the lower ligand of B12

Gordon R O Campbell, Michiko E. Taga, Kavita Mistry, Javier Lloret, Peter J. Anderson, John R. Roth, Graham C. Walker

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


An insight into a previously unknown step in B12 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 B12 (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 B12 (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.

Original languageEnglish (US)
Pages (from-to)4634-4639
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number12
StatePublished - Mar 21 2006


  • Bacteria
  • Biosynthesis
  • Cobalamin
  • Symbiosis
  • Vitamin B

ASJC Scopus subject areas

  • Genetics
  • General


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