Characterizing a Novel Manganese Efflux Pump, MntP, Involved in Metal Homeostasis in Escherichia coli

Metals, such as manganese, are essential to all organisms, but maintaining metal homeostasis is important to avoid toxicity due to competition between metals. In Escherichia coli and other bacteria, metal transporters have been well studied and are essential components of metal homeostasis. Until recently, the only manganese transporter identified in E. coli was MntH, an importer. Microarray data from our lab showed a 10-fold mRNA increase of mntP, a gene of previously unknown function, when cells were incubated with MnCl₂. We found that MntP has homology to other efflux pumps in bacteria and deletion of mntP caused sensitivity to otherwise non-toxic concentrations of manganese. We propose that MntP is a novel manganese efflux pump in E. coli.

Interestingly, the long and conserved 5’ untranslated region (UTR) of mntP contains a riboswitch that may be involved in regulating gene expression of mntP by also sensing manganese. To test this, we constructed translational and transcriptional reporter fusions containing the promoter and the 5’UTR of mntP. Incubating strains bearing the translational or transcriptional fusions with MnCl₂ resulted in a 10-fold or 2-fold increase in reporter expression, respectively. However, no change was seen for other metals, such as iron. This suggests a specific response to manganese by the promoter and the 5’UTR of mntP. Future experiments will characterize the regulation of mntP in response to manganese in combination with other metals and test the contributions of different regions of the promoter and 5’UTR. This research will provide new insights into metal homeostasis in bacteria.