Enterococcus faecium H1激发霍乱弧菌在肠道环境条件下VPI-1/TCP毒力岛水平转移的分子机制

Vibrio cholerae is a human pathogen which colonizes small intestines of host, resulting in the onset of a severe diarrheal disease known as cholera. In order for V. cholerae to successfully colonize the host, it must express a series of virulence factors, including toxin-coregulated pilus (TCP). The genes involves in the biosynthesis of TCP reside in a pathogenicity island, called “VPI-1/TCP island”. However, how V. cholerae aquire and transfer this island is not known. In our preliminary studies, using an infant mouse model, we discovered that the.horizontal transfer of VPI-1/TCP island occurs in host small intestines and requires a member of gut microbiota, identified as Enterococcus faecium. Based on these results,we hypothesize that signals from mammalian hosts and gut microbiota initiate VPI-1/TCP horizontal transfers and provide TCP- V. cholerae selective advantages once aquired TCP. In this application, we will use genomics, genetics, and biochemical approaches to further study the molecular mechanisms of VPI-1/TCP island horizontal transfer. Our studies will shed lights on evolutionary bases of emerging and re-emerging of infectious agents.

霍乱弧菌曾造成7次世界性霍乱流行，至今仍肆虐人间。霍乱弧菌基因组上有许多来源于其他微生物的大片段基因簇，编码与体内定殖及发病症状相关的基因，称为“毒力岛”。霍乱弧菌毒力岛的基因水平转移导致霍乱弧菌毒力进化上的“量子跃迁”，是霍乱病在地球上周期性爆发的关键原因。霍乱弧菌在动物宿主体内定殖依赖TCP纤毛的存在，tcp基因簇分布在VPI-1/TCP毒力岛上，但该毒力岛如何转移一直是霍乱弧菌领域的未解之谜，制约着对霍乱弧菌分子进化的认识和对霍乱病的控制。我们在前期研究中发现，霍乱弧菌VPI-1/TCP毒力岛的水平转移需要满足两个条件：供体菌和受体菌必须共存；选择压力必须有利于供体菌的生存。我们发现肠道微生物能够帮助霍乱弧菌VPI-1/TCP毒力岛在幼鼠肠道内实现水平转移。在此基础上，我们将进一步研究霍乱弧菌VPI-1/TCP的生化本质和水平转移的调控机制，为最终阐明霍乱弧菌的毒力进化机制奠定基础。

霍乱弧菌可以通过基因水平转移获得多种基因岛实现毒力的跃迁，抵御逆境环境而快速定殖。本研究通过构建粪菌移植的乳鼠动物模型、肠道菌库的筛选、磁性几丁质球回收技术，尚无非常详实的证据解释VPI-1/TCP毒力岛水平转移的分子机制。但通过磁性几丁质球回收技术，检测了霍乱弧菌的基因表达，发现了霍乱弧菌能够响应肠道微生物产生的甲酸信号，启动抗逆基因表达。同时，我们对公共数据库的RNAseq和Microarray数据进行了跨平台分析，确定了霍乱弧菌体外应激处理、基因操作和体外培养的重要功能模块，功能模块hubgene的分析显示了临床人类样本的独特性。此外，我们还综述了肠道微生物与霍乱弧菌在VI型分泌系统、群体感应、ROS/pH、生物活性物质方面的相互作用。最后，我们研究了flrA调控的不同靶标基因在成年小鼠体内定殖的能力发现，是FlgM蛋白分泌而不是游动性，通过群体感应系统和甲硫氨酸代谢促进了霍乱弧菌在肠道内的定殖。我们的研究为阐明霍乱弧菌流行和致病分子机理奠定了基础。