柱状黄杆菌的IX型分泌系统结构蛋白及其分泌机制

Bacterial secretion systems are sophisticated multiple-protein complex to secret a wide range of substrates and can be characterized into nine types, i.e. type I – IX secretion system (T1SS-T9SS). They are important for many pathogenic bacteria to export various virulence factors to infect host. T9SS, formerly designated the Por secretion system, is the most recently discovered system. It is conserved in many species within the Bacteroidetes phylum. Flavobacterium columnare, which is the member of Bacteroidetes phylum, is the causative agent of columnaris disease and can infect almost all the fish in freshwater. However, the pathogenesis of this important pathogen has not been elucidated yet. Based on our unpublished data, the genes encoding T9SS not only exist in the F. columnare genome, but also have been identified to be closely related to the virulence of the pathogen for the first time by using deletion strategy. This proposed research is thus designed to understand the genetic diversity T9SS in F. columnare, to probe the novel components of T9SS and to investigated the structural composition and secretory mechanism of F. columnare T9SS. It is believed that this proposed research will for the first time not only provide the novel information about secretion system in F. columnare, but also contribute to our understanding of molecular mechanism for F. columnare invading and infecting hosts, being thus significantly important in promoting the control of colmnaris.

细菌的分泌系统是许多病原菌借以分泌效应分子并侵染宿主的重要分泌装置，分为I–IX型（Type I–IX secretion systems, T1SS–T9SS）。T9SS是最新发现的分泌系统，目前只报道于拟杆菌门（Bacteroidetes phylum）。柱状黄杆菌（Flavobacterium columnare）是拟杆菌门的一种重要鱼类致病菌，引发的柱形病（又称细菌性烂鳃病）严重危害淡水养殖业。我们研究发现该菌具有T9SS的结构基因，并首次通过缺失突变证实了T9SS与细菌毒力密切相关。本项目将在此基础上，对柱状黄杆菌的T9SS结构蛋白及分泌机制开展研究，阐明T9SS在该菌三种基因组型（genomovar）中的分布，揭示T9SS的新型结构蛋白及功能，解析T9SS的结构组成和分泌机制。本项目的完成将填补国内外在柱状黄杆菌分泌系统研究领域的空白，也将为柱形病的防治提供更科学的理论指导。

柱状黄杆菌是鱼类柱形病（在我国也称为细菌烂鳃病）的病原。在全球范围内均有分布，是严重危害淡水鱼类健康养殖的细菌性病原。目前，对该菌的致病机制知之甚少。本团队已发现细菌的IX型分泌系统（type IX secretion system, T9SS）在柱状黄杆菌致病过程中发挥主要作用。但是，T9SS作为细菌分泌系统家族的新成员，有许多问题亟待解答。因此，本项目以柱状黄杆菌为研究对象，围绕其T9SS的结构蛋白、效应分子及分泌机制开展研究。1）发现已报道T9SS的结构蛋白在柱状黄杆菌三种基因组型的菌株中均有分布，是柱状黄杆菌感染宿主必需的分泌系统。2）发现2个新型T9SS结构蛋白TssC和Fsi1，还发现3个新型效应分子Ctl1、Ctl2和Fse。3）解析了T9SS新型结构蛋白功能、与已知的核心结构蛋白之间的关系；阐明了以及新型效应分子功能及分泌机制。4）重新绘制了T9SS的结构模式图。本项目的研究结果，将丰富对于T9SS结构蛋白和效应分子的认识，特别是对重新认识T9SS的结构组成和分泌机制具有重要意义。同时也将对柱状黄杆菌致病机制研究和柱形病防治起到积极的推动作用。