Native plasmid-encoded mercury resistance genes are functional and demonstrate natural transformation in environmental bacterial isolates
2019
Plasmid-mediated
horizontal gene transfer(HGT) is a major driver of genetic diversity in bacteria. We experimentally validated the function of a putative mercury resistance operon present on an abundant 8 kilobase pair native
plasmidfound in groundwater samples without detectable levels of mercury. Phylogenetic analyses of the
plasmid-encoded mercury reductases from the studied groundwater site show them to be distinct from those reported in proximal metal-contaminated sites. We synthesized the entire native
plasmidand demonstrated that the
plasmidwas sufficient to confer functional mercury resistance in Escherichia coli. Given the possibility that
natural transformationis a prevalent HGT mechanism in the low cell density environments of groundwaters, we also assayed bacterial strains from this environment for competence. We used the native
plasmid-encoded metal resistance to design a screen and identified 17 strains positive for
natural transformation. We selected 2 of the positive strains along with a model bacterium to fully confirm HGT via
natural transformation. From an ecological perspective, the role of the native
plasmidpopulation in providing advantageous traits combined with the microbiome9s capacity to take up
environmental DNAenables rapid adaptation to environmental stresses.
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