Regulatory cross-talk supports resistance to Zn intoxication in Streptococcus

Metals such as copper (Cu) and zinc (Zn) are important trace elements that can effect bacterial cell physiology but can also intoxicate bacteria at high concentrations. Discrete genetic systems for management of Cu and Zn efflux have been described in several bacteria pathogens, including streptococci. However, insight into molecular cross-talk between systems for Cu and Zn management in bacteria that drive metal detoxification, is limited. Here, we describe a biologically consequential cross-system effect of metal management in group B Streptococcus (GBS) governed by the Cu-responsive copY regulator in response to Zn. RNAseq analysis of wild-type (WT) and copY-deficient GBS exposed to metal stress revealed unique transcriptional links between the systems for Cu and Zn detoxification. We show that the Cu-sensing functions of CopY extend beyond Cu, and enable CopY to regulate Cu and Zn stress responses to effect genes involved in central cellular processes, including riboflavin synthesis. CopY also contributed to supporting GBS virulence in vivo following infection of mice. Identification of the Zn resistome of GBS using TraDIS revealed a suite of genes essential for GBS growth in metal stress. Several of the genes identified are novel to systems that support bacterial survival in metal stress, and represent a diversity of mechanisms of microbial metal homeostasis during cell stress. Overall, this study reveals a new and important mechanism of cross-system complexity driven by CopY in bacteria to regulate cell management of metal stress and survival. Author SummaryMetals, such as Cu and Zn, can be used by the mammalian immune system to target bacterial pathogens, and consequently, bacteria have evolved discrete genetic systems that subvert this host-derived antimicrobial response. Systems for Cu and Zn homeostasis are well characterized, including the transcriptional control of sensing and responding to metal stress. Here we have discovered novel features of metal response sytems in Streptococcus that have major implications for pathogenesis and virulence. We show that Streptococcus resists Zn intoxication by utilizing a bona fide Cu regulator, CopY, to maintain cellular metal homeostasis, which enables the bacteria to survive stressful conditions. We identify new genes in Streptococcus that confer resistance to zinc intoxication, including several that have not previously been linked to metal ion homeostasis in any bacterium. The identification of cross-system metal management and new resistance mechanisms enhances our understanding of metal ion homeostasis in bacteria and its effect on pathogenesis.