• Herzberg, Martin
• Fischer, Martin
• Schuermann, Jacqueline
• Schuster, Christopher F.
• Layer, Franziska
• Werner, Guido
• Reemtsma, Thorsten
• Strommenger, Birgit

Abstract

<jats:title>ABSTRACT</jats:title><jats:sec><jats:title/><jats:p>Metals are essential for all living organisms, but the type of metal and its concentration determines its action. Even low concentrations of metals may have toxic effects on organisms and therefore exhibit antimicrobial activities. In this study, we investigate the evolutionary adaptation processes of<jats:italic>Staphylococcus aureus</jats:italic>to metals and common genes for metal tolerance. Laboratory and clinical isolates were treated with manganese, cobalt, zinc, or nickel metal salts to generate growth-adapted mutants. After growth in medium supplemented with zinc, whole-genome sequencing identified, among others, two genes,<jats:italic>mgtE</jats:italic>(SAUSA300_0910)<jats:italic><jats:sc>,</jats:sc></jats:italic>a putative magnesium transporter and<jats:italic>spoVG</jats:italic>(SAUSA300_0475), a global transcriptional regulator, as hot spots for stress-induced single-nucleotide polymorphisms (SNPs). SNPs in<jats:italic>mgtE</jats:italic>were also detected in mutants treated with high levels of cobalt or nickel salts. To investigate the effect of these genes on metal tolerance, deletion mutants and complementation strains in an<jats:italic>S. aureus</jats:italic>USA300 LAC* laboratory strain were generated. Both, the<jats:italic>mgtE</jats:italic>and<jats:italic>spoVG</jats:italic>deletion strains were more tolerant to cobalt, manganese, and zinc. The<jats:italic>mgtE</jats:italic>mutant was also more tolerant to nickel exposure. Inductively coupled plasma mass spectrometry analysis demonstrated that the<jats:italic>mgtE</jats:italic>deletion mutant accumulated less intracellular zinc than the wild type, explaining increased tolerance. From these results, we conclude that<jats:italic>mgtE</jats:italic>gene inactivation increases zinc tolerance presumably due to reduced uptake of zinc. For the SpoVG mutant, no direct effect on the intracellular zinc concentration was detected, indicating toward different pathways to increase tolerance. Importantly, inactivation of these genes offers a growth advantage in environments containing certain metals, pointing toward a common tolerance mechanism.</jats:p></jats:sec><jats:sec><jats:title>IMPORTANCE</jats:title><jats:p><jats:italic>Staphylococcus aureus</jats:italic>is an opportunistic pathogen causing tremendous public health burden and high mortality in invasive infections. Treatment is becoming increasingly difficult due to antimicrobial resistances. The use of metals in animal husbandry and aquaculture to reduce bacterial growth and subsequent acquisition of metal resistances has been shown to co-select for antimicrobial resistance. Therefore, understanding adaptive mechanisms that help<jats:italic>S. aureus</jats:italic>to survive metal exposure is essential. Using a screening approach, we were able to identify two genes encoding the transporter MgtE and the transcriptional regulator SpoVG, which conferred increased tolerance to specific metals such as zinc when inactivated. Further testing showed that the deletion of<jats:italic>mgtE</jats:italic>leads to reduced intracellular zinc levels, suggesting a role in zinc uptake. The accumulation of mutations in these genes when exposed to other metals suggests that inactivation of these genes could be a common mechanism for intrinsic tolerance to certain metals.</jats:p></jats:sec>

Topics

• impedance spectroscopy
• nickel
• Magnesium
• Magnesium
• zinc
• laser emission spectroscopy
• cobalt
• size-exclusion chromatography
• Manganese
• spectrometry
• inductively coupled plasma mass spectrometry