Abstract
Zinc is an essential trace element for all living organisms and plays pivotal roles in various cellular processes. However, an excess of zinc is extremely deleterious to cells. Bacteria have evolved complex machineries (such as efflux/influx systems) to control the concentration at levels appropriate for the maintenance of zinc homeostasis in cells and adaptation to the environment. The Zur (zinc uptake regulator) protein is one of these functional members involved in the precise control of zinc homeostasis. Here we identified a zur homologue designated 310 from Streptococcus suis serotype 2, strain 05ZYH33, a highly invasive isolate causing streptococcal toxic shock syndrome. Biochemical analysis revealed that the protein product of gene 310 exists as a dimer form and carries zinc ions. An isogenic gene replacement mutant of gene 310, the Delta310 mutant, was obtained by homologous recombination. Physiological tests demonstrated that the Delta310 mutant is specifically sensitive to Zn(2+), while functional complementation of the Delta310 mutant can restore its duration capability, suggesting that 310 is a functional member of the Zur family. Two-dimensional electrophoresis indicated that nine proteins in the Delta310 mutant are overexpressed in comparison with those in the wild type. DNA microarray analyses suggested that 121 genes in the Delta310 mutant are affected, of which 72 genes are upregulated and 49 are downregulated. The transcriptome of S. suis serotype 2 with high Zn(2+) concentrations also showed 117 differentially expressed genes, with 71 upregulated and 46 downregulated. Surprisingly, more than 70% of the genes differentially expressed in the Delta310 mutant were the same as those in S. suis serotype 2 that were differentially expressed in response to high Zn(2+) concentration, consistent with the notion that 310 is involved in zinc homeostasis. We thus report for the first time a novel zinc-responsive regulator, Zur, from Streptococcus suis serotype 2.