Cobalt and nickel ion synergy promotes gene amplification and stable metal resistance in

Microbial species are integral in environmental homeostasis and have thus developed diverse strategies to adapt, survive, and proliferate under exogenous stress. The growing demand for nanoscale battery materials has led to increasing environmental concentrations of nanomaterials and their constituent metal ions. Previous work has shown that the Gram-negative bacterium IMPORTANCE: Studying mechanisms of microbial resistance evolution is critical for understanding the role of bacteria in the environment and developing new strategies to combat antimicrobial resistance to modern therapeutics. Technological innovation has often led to the introduction of novel environmental stressors that impart pressure on microbes to evolve resistance. This may ultimately lead to novel resistance genes or gene cassettes in the environmental gene pool, which could further promote antimicrobial resistance in pathogenic organisms. In this study, we highlight the importance of considering gene amplification as a mechanism of bacterial resistance to environmental toxins. We demonstrate that amplification events can exist within a population in the absence of selection pressure and without a clear fitness cost. Identifying specific stimuli that trigger these events will help us understand factors that accelerate bacterial resistance evolution and have the potential to disrupt ecosystem balance.