Analysis of genomic data extracted from evolution experiments.

The lack of new antibiotics and the ability of bacteria to quickly adapt to stressful conditions, such as exposure to antimicrobial compounds in their natural environment, has brought humanity to an antibiotic crisis. An additional concern is that other biocides, such as heavy metals, can put microorganisms under selective pressures that trigger them to evolve to resistant phenotypes. In this study we examined co-selection for antibiotic and heavy metal resistance in an environmental urban isolate of Bacillus pumilus. In a series of experimental evolution incubations, we observed how the exposure to progressively higher concentrations of zinc sulfate in the growth media lead to emergence of a bacterial phenotype more tolerant against all antibiotics tested. On the other hand, our control line showed an increase in susceptibility against antibiotics after simply growing in laboratory conditions. We further identified the genetic and phenotypic changes that occured during the experimental evolution as a potential protective measure against both antibiotics and heavy metals.