The manganese-responsive regulator MntR represses transcription of a predicted ZIP family metal ion transporter in Corynebacterium glutamicum

Manganese is an important trace element required as an enzyme cofactor and for protection against oxidative stress. In this study, we characterized the DtxR-type transcriptional regulator MntR (cg0741) of Corynebacterium glutamicum ATCC 13032 as a manganese-dependent repressor of the predicted ZIP family metal transporter Cg1623. Comparative transcriptome analysis of a ΔmntR strain and the wild type led to the identification of cg1623 as potential target gene of MntR which was about 50-fold upregulated when cells were grown in glucose minimal medium. Using electrophoretic mobility shift assays, a conserved 18 bp inverted repeat (TGTTCAATGCGTTGAACA) was identified as binding motif of MntR in the cg1623 promoter and confirmed by mutational analysis. Promoter fusion of Pcg1623 to eyfp confirmed that the MntR-dependent repression is only abolished in the absence of manganese. However, neither deletion of mntR nor cg1623 resulted in a significant growth phenotype in comparison to the wild type--strongly suggesting the presence of further manganese uptake and efflux systems in C. glutamicum. The control of cg1623 by the DtxR-type regulator MntR represents the first example of a predicted ZIP family protein that is regulated in a manganese-dependent manner in bacteria.