The five homologous CiaR-controlled Ccn sRNAs of modulate Zn-resistance.

Zinc is a vital transition metal for , but is deadly at high concentrations. In , elevated intracellular free Zn levels result in mis-metallation of key Mn-dependent metabolic and superoxide detoxifying enzymes resulting in Zn intoxication. Here, we report our identification and characterization of the function of the five homologous, CiaRH-regulated Ccn sRNAs in controlling virulence and metal homeostasis. We show that deletion of all five genes (, , , , and ) from strains D39 (serotype 2) and TIGR4 (serotype 4) causes Zn hypersensitivity and an attenuation of virulence in a murine invasive pneumonia model. We provide evidence that bioavailable Zn disproportionately increases in strains lacking the five genes. Consistent with a response to Zn intoxication or relatively high intracellular free Zn levels, expression of genes encoding the CzcD Zn exporter and the Mn-independent ribonucleotide reductase, NrdD-NrdG, were increased in the Δ mutant relative to its isogenic parent strain. The growth inhibition by Zn that occurs as the result of loss of the genes is rescued by supplementation with Mn or Oxyrase, a reagent that removes dissolved oxygen. Lastly, we found that the Zn-dependent growth inhibition of the Δ strain was not altered by deletion of , whereas the Δ strain phenocopied the Δ strain. Overall, our results indicate that the Ccn sRNAs have a crucial role in preventing Zn intoxication in .