无乳链球菌(Streptococcus agalactiae)是重要的人兽鱼共患菌。近年来，罗非鱼无乳链球菌病日益严重，对其产业造成极大的危害。磷酸转移酶系统 (PTS) 在细菌碳水化合物转运和代谢过程中发挥重要作用，被视为细菌“神经系统”。项目组通过蛋白组学和基因转录分析发现：纤维二糖-PTS系统的cel-EⅡB蛋白在无乳链球菌弱毒株中过表达，推测cel-EⅡB蛋白介导PTS系统调控无乳链球菌的毒力。本项目拟采用基因敲除技术，评价无乳链球菌强、弱毒株cel-EⅡB蛋白缺失后其生物学特性变化及其对宿主毒力的影响；通过RT-qPCR与生物信息学的方法，分析cel-EⅡB蛋白对PTS代谢通路基因、二元信号转导系统基因以及下游毒力基因表达的响应，进一步解析cel-EⅡB蛋白介导PTS系统调控细菌毒力的分子机制。本项目的实施将丰富无乳链球菌毒力调控机制研究。

Streptococcus agalactiae is an important pathogen associated with human, animals and fish. In recent years, it has spread around the world, resulting in great economic losses in Tilapia-industries. Phosphotransferase system (PTS) is regarded as the "nervous system" of bacteria. In our previous studies, the cel-EⅡB protein, an enzyme of cel-PTS, was over expressing in attenuated S. agalactiae strain using proteomics and gene transcription analysis, suggesting that it may be involving in regulating the bacterial virulence. In this research, we plan to evaluate cel-EⅡB protein ediated PTS system in regulating the bacterial virulence with the biological characteristics and virulence changes using gene knockout technology. Base on the method of RT-qPCR and bioinformatics, we tries to testify the cel-EⅡB protein play important role in effecting the gene expression patterns of the PTS metabolic pathways, two signal transduction system (TCS) and virulence proteins. Importantly, this study tries to analyze the molecular mechanisms of cel-EⅡB protein ediated PTS system in regulating of bacterial virulence. Our findings will enrich the theory of the virulence regulation mechanism of Streptococcus agalactiae.