Rapid Evolution of Zinc Resistance in Escherichia coli and Its Consequences
AbstractZinc (Zn) is ubiquitously present in the environment and cells where it is a nutritionally essential mineral needed for a variety of biological processes. However, excess Zn acts as an antimicrobial agent inhibiting the growth of a wide spectrum of microorganisms notably pathogens. This property is exploited in several industries. Resistance to excess Zn is particularly of interest because it provides insight into homeostatic control to regulate entry and exit of Zn. In this study, we utilized experimental evolution to determine how quickly E. coli evolved resistance to excess Zn with subsequent genomic analysis. Phenotypic assays were also conducted to demonstrate trade-off and pleiotropic consequences associated with resistance to excess Zn. Herein, we demonstrated that at 7 days of selection, populations cultured in excess Zn displayed a significant (P<0.05) increase in 24-h growth compared to the control populations. Likewise, these populations showed an increase in resistance in Magnesium sulfate and Copper (II) sulfate. In contrast, Zn-resistance evolved trade-off to iron (II) sulfate, ampicillin, and tetracycline. Genomic analysis of Zn resistance identified polymorphisms and hard selective sweeps in mlrA (transcriptional activator), Rhs (family putative polymorphic toxin), aspU (tRNA‑Asp/2,5‑diketo‑D‑gluconate reductase B) and rpoA (RNA polymerase alpha subunit). Collectively, these results show that E. coli can rapidly evolve resistance to excess Zn with pleotropic and trade-offs consequences associated with this adaptation. Interactions between bacteria and heavy metal ions are of great interest both as a fundamental process and potential bioremedial technology.
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