Comparative Genomic Analysis Reveals the Distribution, Organization, and Evolution of Metal Resistance Genes in the Genus .

Members of the genus , which can adapt to extremely high concentrations of heavy metals, are universally found at acid mine drainage (AMD) sites. Here, we performed a comparative genomic analysis of 37 strains within the genus to answer the untouched questions as to the mechanisms and the evolutionary history of metal resistance genes in spp. The results showed that the evolutionary history of metal resistance genes in spp. involved a combination of gene gains and losses, horizontal gene transfer (HGT), and gene duplication. Phylogenetic analyses revealed that metal resistance genes in spp. were acquired by early HGT events from species that shared habitats with spp., such as , , , and species. Multicopper oxidase genes involved in copper detoxification were lost in iron-oxidizing , , and and were replaced by rusticyanin genes during evolution. In addition, widespread purifying selection and the predicted high expression levels emphasized the indispensable roles of metal resistance genes in the ability of spp. to adapt to harsh environments. Altogether, the results suggested that spp. recruited and consolidated additional novel functionalities during the adaption to challenging environments via HGT, gene duplication, and purifying selection. This study sheds light on the distribution, organization, functionality, and complex evolutionary history of metal resistance genes in spp. Horizontal gene transfer (HGT), natural selection, and gene duplication are three main engines that drive the adaptive evolution of microbial genomes. Previous studies indicated that HGT was a main adaptive mechanism in acidophiles to cope with heavy-metal-rich environments. However, evidences of HGT in species in response to challenging metal-rich environments and the mechanisms addressing how metal resistance genes originated and evolved in are still lacking. The findings of this study revealed a fascinating phenomenon of putative cross-phylum HGT, suggesting that spp. recruited and consolidated additional novel functionalities during the adaption to challenging environments via HGT, gene duplication, and purifying selection. Altogether, the insights gained in this study have improved our understanding of the metal resistance strategies of spp.