金黄色葡萄球菌Agr调控壁磷壁酸核糖醇链长和糖基修饰抵御噬菌体感染的分子机制

Phages, short for bacteriophages, are bacteria-specific viruses that have been used as a treatment against certain pathogens. However, lots of research have found that bacteria evolve a variety of mechanisms to protect against phage infection, among which the change of phage receptor (such as cell wall teichoic acid, WTA) structure is one of the most important mechanism. RNAIII, a small RNA that is the effector of the Staphylococcus aureus (S. aureus) accessory gene regulator (Agr) controlling the expression of a large number of virulence genes. Our preliminary data found that, under pressure of phage infection, bacterial RNAIII was significantly inhibited, and the expressions of WTA ribitol-related synthetases (including polymerase and glycosyltransferase) were down-regulated, and the ability of the bacteria resistance to phage infection was significantly enhanced. To determine the role of the Agr system in the process of bacterial resistance to phage infection, this project will explore the molecular basis of inhibition of Agr function by small molecule proteins secreted by phage-infected S. aureus by coimmunoprecipitation and mass spectrometry. By electrophoretic mobility shift assay (EMSA), RNA pull-down, and other molecular biotechnology, the mechanism of WTA ribitol-related polymerases and glycosyltransferases regulated by RNAIII will be studied with the phage infection; By the analysis of nuclear magnetic resonance spectroscopy, we will reveal the molecular mechanism that S. aureus resistant to phage infection by changing the length and the glycosylation of WTA ribitol which is caused by the expression of WTA ribitol-related polymerases and glycosyltransferases. Taken together, our results provide insight on the molecular and regulatory mechanism of S. aureus that is resistant to phage infection by Agr-mediated structure and glycosylation change of WTA ribitol, which will contribute to develop novel therapeutic against S. aureus phages.

噬菌体侵染细菌，细菌也演化出多种抵御噬菌体感染的机制。我们研究发现，随着噬菌体感染进程的加深，金黄色葡萄球菌附属基因调节子（Agr）受到显著抑制、噬菌体受体—壁磷壁酸（WTA）核糖醇的相关合成酶（聚合酶和糖基转移酶）表达下调、细菌抵御噬菌体感染的能力显著增强。为阐明Agr在细菌抵抗噬菌体感染过程中发挥的作用及机制，本项目拟通过质谱分析等技术，探究噬菌体感染细菌后分泌的小分子蛋白抑制Agr表达的分子机制；通过RNA pull-down等技术，研究在噬菌体压力下，Agr系统对WTA核糖醇相关合成酶的调控作用；通过核磁共振波谱等技术，揭示细菌WTA核糖醇相关合成酶通过影响WTA核糖醇链长和糖基修饰抵抗噬菌体感染的分子基础。最终阐明噬菌体感染金黄色葡萄球菌后，通过分泌信号分子介导Agr调控WTA核糖醇的结构与修饰进而抵御噬菌体感染的分子机制，为研发金黄色葡萄球菌新型噬菌体抗菌制剂提供理论依据。

噬菌体侵染细菌，细菌也演化出多种抵御噬菌体感染的机制。本研究通过代谢组学和蛋白组学等技术，发现耐甲氧西林金黄色葡萄球菌（MRSA）与短尾噬菌体SLPW作用后的代谢产物能够激活细菌agr双组分系统效应分子RNAⅢ的表达。进一步研究发现，agr系统的激活后诱导MRSA菌株多种细胞壁壁磷壁酸（WTA）合成酶表达下调，导致WTA骨架CDP-核糖醇合成受阻，最终致使以CDP-核糖醇作为受体的噬菌体侵染细菌能力下降。以上研究表明agr是金黄色葡萄球菌操控噬菌体吸附感染的关键系统。此外，本研究通过噬菌体的环境消杀实验和体内抗菌实验，发现金黄色葡萄球菌噬菌体能够有效杀灭环境中的葡萄球菌，同时能够有效治疗MRSA引起的奶牛乳腺炎。