MntR regulon.
The genomes of R. capsulatus and M. loti lack the fur/mur gene but do contain a copy of the mntR gene, located next to mntH. This suggests that, in contrast to many other α-proteobacteria with Mur, the uptake of Mn2+ in these two species is regulated by MntR, an ortholog of the Mn2+-sensing transcriptional regulator from E. coli and B. subtilis [22,23]. By applying the signal detection procedure to 5′ regions of the mntH genes from the MntR-containing genomes of α-proteobacteria, we identified a 20-bp palindromic motif (Figure 8; Table S5), which is similar to the consensus MntR-binding site in enterobacteria (5′-AACATAGCnnnnGCTATGTT-3′) [23]. The presence of mntR in the genome of Mesorhizobium sp. BNC1 is enigmatic since the only candidate MntR-binding site was found upstream of mntR itself, suggesting its autoregulation, whereas Mn2+ uptake transporters in this species (mntH and sit) are likely under the control of Mur. Interestingly, the Bradyrhizobium sp. strain BTAi1 has two mntH paralogs, one of which is a candidate member of the Mur/Fur regulon and has an MRS-like sequence, and the other one of which is preceded by a strong candidate MntR-binding site.
Figure 8  Sequence Logos for the Predicted MntR Recognition Motifs in α-Proteobacteria

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