Polyphyletic origins of bacterial Nramp transporters

The redox-active metals iron and manganese are required for energy metaboli sm, protection against oxidative stress and defense against infections. In eukaryotes, both divalent metals are transported by Nramp transporters. The sequence of these transporters was remarkably conserved during evolution. Several bacterial Nramp homologs (MntH) are also proton-dependent manganese transporters. Here, we present phylogenetic evidence for the polyphyletic origins of three groups of MntH proteins and for possible Nramp horizontal gene transfer with eukaryotes. We propose that the evolution of the MntH/Nr amp family is related to adaptation to oxidative environments, including th ose arising during infection of animals and plants.