Regulation ofSalmonella entericaSerovar TyphimuriummntHTranscription by H2O2, Fe2+, and Mn2+

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Abstract
MntH, a bacterial homolog of mammalian natural resistance associated macrophage protein 1 (Nramp1), is a primary transporter for Mn2+influx inSalmonellaentericaserovar Typhimurium andEscherichia coli. S. entericaserovar Typhimurium MntH contributes to H2O2resistance and is important for full virulence. Consistent with its phenotype and function,mntHis regulated at the transcriptional level by both H2O2and substrate cation. We have now identified threetrans-acting regulatory factors and the three correspondingcis-actingmntHpromoter motifs that mediate this regulation. In the presence of hydrogen peroxide,mntHis activated by OxyR, acting through an OxyR-binding motif centered just upstream of the likely −35 RNA polymerase-binding site. In the presence of Fe2+,mntHis repressed primarily by Fur, acting through a Fur-binding motif overlapping the −35 region. In the presence of Mn2+,mntHis repressed primarily by theSalmonellaequivalent ofE. colib0817, a distant homolog of theBacillus subtilismanganese transport repressor, MntR, acting through an inverted-repeat motif located between the likely −10 polymerase binding site and the ribosome binding site.E. colib0817 was recently shown to bind the identical inverted-repeat motif in theE. coli mntHpromoter and hence has been renamed MntR (S. I. Patzer and K. Hantke, J. Bacteriol.183:4806-4813, 2001). Using Δfur, ΔmntR, and ΔfurΔmntRmutant strains as well as mutations in the Fur- and MntR-binding motif elements, we found that Fe2+can also mediate repression through the Mn2+repressor MntR.