Functional Characterization Of Rel_Ss And PerR Genes From Streptococcus Suis Serotype2

Streptococcus suis is economically a very important Gram-positive and facultative anaerobic bacterium that causes severe diseases in pigs and humans. As an emerging zoonotic pathogen, S. suis serotype2has become the predominant causative agent of adult human meningitis in Vietnam and Hong Kong. Two large outbreaks of human infections were reported in China in1998and2005, resulting in229infections and52deaths. Like other bacterial pathogens, S. suis may also encounter various kinds of stress during infection, such as nutrition starvation, iron limition and oxidative stress. In the previous studies in our lab, we has found that relss and perR in S. suis were differential expressing in the simulative iron starvation condition, suggesting that they may play a role on stress adaption during infection. In our study, the further researches on relss and perR were carried on in S. suis.1. The research on the function of relss in S. suis serotype2Bacteria have evolved efficient stress responses to adapt the changes of environment and nutrition starvation, among these responses, a special class of adaptive response induced by (p)ppGpp is called "stringent response". In bacteria,(p)ppGpp is produced by RelA/SpoT homologue proteins. Classic stringent response was induced by ribosome idling reaction when amino acid was depleted. However, stringent response in other conditions were less studied. We have found a RelA/SpoT homologous protein Relss and a small (p)ppGpp synthetase RelQ in SS2genome. In previous study in our lab, we have found that relss was up-regulated during iron starvation. In this study, we found that (p)ppGpp could be accumulated not only during amino acid starvation but also during iron limitation and glucose starvation. Relss is the sole source of (p)ppGpp synthesis during glucose starvation, while Relss and a small (p)ppGpp synthetase RelQ are both in charge for (p)ppGpp synthesis during amino acid starvation and during iron starvation.We futher studied the stringent response and its mechanism induced by glucose starvation by comparing the expression changes of SC-19and Arelss during glucose starvation. We found that, For long time survival, Relss did not only affect the classic stringent response, such as inhibition of DNA replication and protein synthesis, through repressing the expression of genes in glycolysis, carbon catabolite repression (CCR) systems were also activated for using other carbon sources instead of glucose. These results completely showed the adaptive regulation mediated by Relss during glucose starvation in SS2, and preliminarily revealed the mechanism for inducing stringent response during glucose starvation. This study is a good foundation for studying on stringent response during carbon starvation in bacteria, especially in G+bacteria. Furthermore, mice infection experiment showed that the pathogenicity of Arelss was attenuated.2. The research on the function of perR in S. suis serotype2Metal ions are important micronutrients in cellular metabolism, but excess ions that cause toxic reactive oxygen species are harmful to cells. In bacteria, Fur family proteins such as Fur, Zur and PerR manage the iron and zinc uptake and oxidative stress responses, respectively. The single Fur-like protein (annotated as PerR) in Streptococcus suis has been demonstrated to be involved in zinc and iron uptake in previous studies.In the present study, the perR gene deletion mutant AperR was constructed in S. suis serotype2strain SC-19and we found that PerR also affected the oxidative stress response. Additional, dpr gene and metQIN operon were proved to be directly regulated by PerR by real-time RT-PCR and Electrophoretic mobility shift assays, dpr encodes a Dps-like peroxide resistance protein, and the dpr knockout strains(â–³dpr andâ–³dprâ–³perR) were highly sensitive to H2O2. MetNIQ is a methionine transporter, and the increased utilization of methionine in the AperR strain indirectly affected the peroxide resistance. Using a promoter-EGFP gene fusion reporting system, we found that the PerR regulon was induced by H2O2, and the induction was modulated by metal ions. Finally, we found that the pathogenicity of the perR mutant was attenuated and easily cleared by mice. These data strongly suggested that, besides regulation on iron and zinc utilization, the Fur-like protein PerR regulated the oxidative stress resistance related regulon containing dpr and metQIN and plays a crucial role in oxidative stress response in S. suis.