Transcriptional regulation of Salmochelin glucosyltransferase by Fur in Salmonella.

Pathogenic bacteria acquire the acquisition of iron from the host to ensure their survival. Salmonella spp. utilizes siderophores, including salmochelin, for high affinity aggressive import of iron. Although the iroBCDEN operon is reportedly responsible for the production and the transport of salmochelin, the molecular mechanisms underlying the regulation of its gene expression have not yet been characterized. Here, we analyzed the expression pattern of iroB using the lacZY transcriptional reporter system and determined the transcription start site in response to iron availability using primer extension analysis. We further examined the regulation of iroB expression by the ferric uptake regulator (Fur), a key regulatory protein involved in the maintenance of iron homeostasis in various bacteria, including Salmonella. Using sequence analysis followed by a gel shift assay, we verified that the Fur box lies within the promoter region of iroBCDE. The Fur box contained the consensus sequence (GATATTGGTAATTATTATC) and overlapped with the -10-element region. The expression of iroB was repressed by Fur in the presence of iron, as determined using an in vitro transcription assay. Therefore, we found that the iron acquisition system is regulated in a Fur-dependent manner in Salmonella.