The Irr and RirA Proteins Participate in a Complex Regulatory Circuit and Act in Concert To Modulate Bacterioferritin Expression in Ensifer meliloti 1021.

In this work we found that the gene of the rhizobial species , encoding a bacterioferritin iron storage protein, is involved in iron homeostasis and the oxidative stress response. This gene is located downstream of and overlapping the open reading frame (ORF). No well-predicted RirA or Irr boxes were found in the region immediately upstream of the gene although two presumptive RirA boxes and one presumptive Irr box were present in the putative promoter of We demonstrate that gene expression is enhanced under iron-sufficient conditions and that Irr and RirA modulate this expression. The pattern of gene expression as well as the response to Irr and RirA is inversely correlated to that of Moreover, our results suggest that the small RNA SmelC759 participates in RirA- and Irr-mediated regulation of expression and that additional unknown factors are involved in iron-dependent regulation. belongs to the , a group of bacteria that includes several species able to associate with eukaryotic hosts, from mammals to plants, in a symbiotic or pathogenic manner. Regulation of iron homeostasis in this group of bacteria differs from that found in the well-studied In this work we analyzed the effect of and mutations on gene expression. We demonstrate the effect of an mutation on iron homeostasis in this bacterial genus. Moreover, results obtained indicate a complex regulatory circuit where multiple regulators, including RirA, Irr, the small RNA SmelC759, and still unknown factors, act in concert to balance gene expression.