Eukaryotic Nramp genes encode divalent
metal ion
permeases important for nutrition and resistance to microbial
infection. Bacterial homologs encode
proton-dependent transporters of
manganese (MntH), and other divalent
metal ions. Bacterial MntH were classified in three homology groups (A, B, C) and MntH C further subdivided in Calpha, Cbeta, Cgamma. The
proteins from C. tepidum (MntH B) and E. faecalis (MntH Cbeta1, 2), divergent in sequence and hydropathy profile, conferred increased
metal sensitivity when expressed in E. coli, suggesting conservation of divalent
metal transport function in MntH B and C. Several genomic evidence suggest horizontal gene transfer (HGT) of mntH C genes: (i) The enterobacteria Wigglesworthia mntH Cbeta gene is linked to an Asn t-
RNA, and its sequence most conserved with Gram positive bacteria homologs; (ii) all the Cbeta genes identified in oral streptococcaceae are associated with different potentially mobile
DNA elements; (iii) Lactococcus lactis and Burkholderia mallei genomes contain an mntH gene prematurely terminated and a novel full-length mntH C gene; (iv) remarkable sequence relatedness between the unicellular alga C. reinhardtii "prototype" Nramp and some MntH Calpha (e.g., Nostoc spp., Listeria spp.) suggests HGT between Eukarya and Bacteria. Other "prototype" Nramp genes (intronless, encoding
proteins strongly conserved with MntH A and B
proteins) identified in invertebrates represent a possible source for transfer of Nramp genes toward opportunistic bacteria. This study demonstrates complex evolution of MntH in Bacteria. It is proposed that "prototype" Nramp are ancestors of bacterial MntH C
proteins, which could facilitate
bacterial infection.