Rsp promotes the transcription of virulence factors in an <i>agr</i>-independent manner in <i>Staphylococcus aureus</i>

<i>Staphylococcus aureus</i> is a major human pathogen that causes a great diversity of community- and hospital-acquired infections. Rsp, a member of AraC/XylS family of transcriptional regulators (AFTRs), has been reported to play an important role in the regulation of virulence determinants in <i>S. aureus</i> via an <i>agr</i>-dependent pathway. Here we demonstrated that Rsp could bind to the <i>rsp</i> promoter to positively regulate its own expression. We then constructed an isogenic <i>rsp</i> deletion strain and compared the haemolysis in the wild-type and <i>rsp</i> mutant strains. Our results indicated that the <i>rsp</i> mutant strain displayed decreased haemolytic activity, which was correlated with a dramatic decrease in the expression of <i>hla</i> and <i>psm</i>. Furthermore, we analysed the regulatory effects of Rsp in the <i>agr</i> mutant strain and found that they are <i>agr</i>-independent. Electrophoretic mobility shift assay indicated that Rsp can directly bind to the promoter regions of <i>hla</i> and <i>psm</i>. The mouse model of subcutaneous abscess showed that the <i>rsp</i> mutant strain displayed a significant defect in virulence compared to the wild-type strain. These findings reveal that Rsp positively regulates the virulence of <i>S. aureus</i> by promoting the expression of <i>hla</i> and <i>psm</i> through direct binding to their promoter regions.

金黄色葡萄球菌（Staphylococcus aureus）是一类重要的人类病原菌，可引发多种社区获得性与医院获得性感染。Rsp作为AraC/XylS家族转录调节因子（AraC/XylS family of transcriptional regulators, AFTRs）的成员，此前已有研究证实其可通过agr依赖型通路对金黄色葡萄球菌的毒力决定因子发挥关键调控作用。本研究证实，Rsp可结合rsp基因的启动子区域，对自身的转录表达产生正向调控。随后我们构建了同源rsp缺失菌株，并对比了野生型菌株与rsp突变菌株的溶血活性。实验结果显示，rsp突变菌株的溶血活性显著降低，这与hla以及psm的表达水平大幅下调密切相关。进一步，我们在agr突变菌株中分析了Rsp的调控效应，发现其调控作用不依赖于agr通路。电泳迁移率变动实验表明，Rsp可直接结合hla与psm的启动子区域。小鼠皮下脓肿感染模型结果显示，相较于野生型菌株，rsp突变菌株的毒力存在显著缺陷。本研究结果揭示，Rsp可通过直接结合hla与psm的启动子区域，促进二者的转录表达，从而正向调控金黄色葡萄球菌的毒力。