沉积物慢生单胞菌的捕食特性及捕食机制探究

Predatory interactions are key processes in microbial food webs. The predatory performance and genetic components involved in the predation of the bacterium Bradymonas sediminis was explored, and it could help us understand the importance of predatory bacteria in community succession and material cycle in marine ecosystem. We found that B. sediminis FA350 strain prey on 205 bacteria strains from Gram -negative and -positive bacteria. The genome sequencing of B. sediminis FA350 strain has been completed and analyzed. In this study, we follow the fate of fully 13C-labeled prey cells as a proxy for labile biomass introduced into B. sediminis FA350 cells, demonstrating that B. sediminis is a bacterial predator. Experiments are designed to determine how temperature, pH, the predator-prey ratio and type of prey affect prey killing by B. sediminis. The contact dependent assay are performed to investigate the function of extracellular substances in the predation. Using a random transposon plasmid, we perform a genome-wide genetic screening in B. sediminis FA350 strain to isolate and analyze the mutants, which are defective in their predatory behavior. The insertion sites of these mutants are localized by plasmid rescuing and sequencing. Function of predator genes are analyzed by using bioinformatics method, and are genetic components reflecting the underlying mechanisms of B. sediminis predation.

捕食性相互作用是微生物食物链中的关键过程，探究海洋细菌沉积物慢生单胞菌Bradymonas sediminis的捕食特性及捕食机制，为研究捕食性细菌在海洋生态系统的群落演替和物质循环中的功能奠定基础。前期发现B. sediminis FA350菌株可捕食细菌205株，包括革兰氏阴性和阳性细菌。目前已完成FA350菌株的基因组测序并进行了初步分析。本研究首先利用13C稳定性同位素核酸探针技术进一步确定B. sediminis FA350菌株具有捕食功能，并分析温度、pH、被捕食菌数量和种类等因素对其捕食能力的影响。探究B. sediminis FA350菌株捕食是否依赖细胞接触、有无胞外活性物质产生。随后利用转座子随机插入方法，构建捕食缺陷型突变子文库；使用质粒营救和测序对插入位点进行定位，对该基因的功能进行预测，初步解析沉积物慢生单胞菌的捕食机制。

慢生单胞菌是本课题组于2015年发现的新型捕食性细菌类群，具有重要的生态意义和应用前景。目前已获得9株慢生单胞菌，添加0.15%的丙酮酸钠可以促进生长，其中Lujinxingia vulgaris TMQ2生长最快。这些慢生单胞菌菌株均可捕食多种不同猎物细菌，包括肺炎克雷伯氏菌、副溶血性弧菌、铜绿假单胞菌、鲍曼不动杆菌、金黄色葡萄球菌等。以不同初始比例混合培养时，慢生单胞菌含量越高，其捕食能力越强，具有明显的数量依赖性。在邻近捕食时，慢生单胞菌快速的滑行运动会促进其向猎物更快靠近和侵袭并提高捕食效率。在L. vulgaris TMQ2的捕食压力下传代后副溶血性弧菌G23表现出更强的抗捕食能力，在寡营养和无营养的条件下G23存活能力明显强于G0。G0和G23基因组突变位点分析发现有5个核苷酸位点发生突变，1个位于基因间区，4个位于编码区。这些突变位点可能导致CheW、LysR家族转录调控因子和superfamily 1 DNA helicases异常表达，进而影响G23的生长代谢、趋化运动和生物被膜的形成能力。本课题的研究为进一步揭示慢生单胞菌的新型捕食机制奠定基础，有助于探究慢生单胞菌在海洋微生物群落构建中的关键生态作用、在水产养殖病害防治中的应用。