Cupriavidus metallidurans CH34 adapted to high Zn concentrations

Cupriavidus metallidurans CH34 is a well-studied metal-resistant beta-proteobacterium and contains a battery of genes involved in the resistance and processing of numerous metals. Here, we performed a directed evolution experiment to obtain derivatives adapted to grow in the presence of zinc at concentrations above the minimal inhibitory concentration for the parental strain. Genetic characterization of one derivative, CH34ZnR, which was also more resistant to cadmium, revealed seven mutations, including inactivation of glpR coding for a DeoR-type transcriptional repressor by insertion of IS1088. The latter resulted in the constitutive expression of the neighboring ABC-type transporter. GlpR and the adjacent ABC transporter are highly similar to the glycerol operon regulator and ATP-driven glycerol importer of Rhizobium leguminosarum bv. viciae VF39, respectively. Deletion of glpR or the ABC transporter and complementation of CH34ZnR with the parental glpR gene further demonstrated that loss of GlpR function, with concomitant induction of the adjacent ABC transporter, is pivotal in the observed phenotype. Moreover, addition of glycerol, presumably by glycerol-mediated reduced GlpR activity, also promoted increased zinc and cadmium resistance. Thus, the ABC-type transporter is proposed to be a new adaptation route during exposure to toxic zinc concentrations.