RirA is the iron response regulator of the rhizobactin 1021 biosynthesis and transport genes in Sinorhizobium meliloti 2011

The genes encoding the biosynthesis and transport of rhizobactin 1021, a siderophore produced by Sinorhizobium meliloti, are negatively regulated by iron. Mutagenesis of HrA, the rhizobial iron regulator, resulted in abolition of the iron responsive regulation of the biosynthesis and transport genes. Bioassay analysis revealed that the siderophore is produced in the presence of iron in a rirA mutant. RNA analysis and GFP fusions supported the conclusion that RirA is the mediator of iron-responsive transcriptional repression of the two transcripts encoding the biosynthesis and transport genes. RirA in S. meliloti appears to fulfil the role often observed for Fur in other bacterial species. The regulator was found to mediate the iron-responsive expression of two additional genes, smc02726 and dppA1, repressing the former while activating the latter. The HrA mutant nodulated the host plant Medicago sativa (alfalfa) and fixed nitrogen as effectively as the wild type. (c) 2005 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.