Dissection Of A Novel Metal Resistance Mechanism In Cupriavidus metallidurans

Background:Cupriavidus metallidurans strains contain many genes involved in the resistance and processing of heavy metals, which are very well studied and characterized. In addition, studies at SCK•CEN underscored the rapid evolution of C. metallidurans strains towards significantly increased metal resistance, particularly for silver. Objective:Our objective is to understand the molecular mechanisms of this increased resistance to silver. Methods:C. metallidurans strains including type strain CH34, its plasmidless derivative AE104 and NA4, isolated from a silver-sanitized drinking water system, were grown in toxic levels of silver to obtain silver-resistant mutants. The latter were characterized in detail via re-sequencing, oligonucleotide microarrays, and deletion and complementation analyses.Conclusions:Our data indicate that C. metallidurans is able to adapt rapidly to toxic silver concentrations. Silver-resistant mutants were obtained from different strains, even from strains cured from the main mega-plasmid encoded metal resistance determinants, indicating that the canonical efflux mechanisms are not involved. Whole-genome expression profiling in non-selective growth conditions showed that only a few genes were commonly up-regulated in all obtained silver-resistant mutants. In addition, deletion mutants and plasmid-based complementation confirmed that a two-component regulatory system and a gene coding for a small periplasmic protein play a central role. These results represent a previously uncharacterized molecular mechanism for metal/silver resistance.