Regulation of Salmonella enterica serovar typhimurium mntH transcription by H2O2, Fe2+, and Mn2+

MntH, a bacterial homolog of mammalian natural resistance associated macrophage protein 1 (Nramp1), is a primary transporter for Mn2+ influx in Salmonella enterica serovar Typhimurium and Escherichia coli. S. enterica serovar Typhimurium MntH contributes to H2O2 resistance and is important for full virulence. Consistent with its phenotype and function, mntH is regulated at the transcriptional level by both H2O2 and substrate cation. We have now identified three trans-acting regulatory factors and the three corresponding cis-acting mntH promoter motifs that mediate this regulation. In the presence of hydrogen peroxide, mntH is 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+, mntH is repressed primarily by Fur, acting through a Fur-binding motif overlapping the -35 region. In the presence of Mn2+, mntH is repressed primarily by the Salmonella equivalent of E. coli b0817, a distant homolog of the Bacillus subtilis manganese transport repressor, MntR, acting through an inverted-repeat motif located between the likely -10 polymerase binding site and the ribosome binding site. E. coli b0817 was recently shown to bind the identical inverted-repeat motif in the E. coli mntH promoter and hence has been renamed MntR (S.I. Patzer and K. Hantke, J. Bacteriol. 183:4806-4813, 2001). Using Deltafur, DeltamntR, and Deltafur DeltamntR mutant 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.