海洋玫瑰杆菌群体感应及其退出机制对藻菌关系的调节

Algae-bacteria interactions are the important factors to maintaining dynamic balance of phycosphere. To understand algae-bacteria interactions from the aspect of chemical ecology has become a frontier and hot point for the studies in algological ecology and microecology. Quorum sensing (QS) modulating algae-bacteria interaction mediated by chemical signals has attracted more attentions. Marine Roseobacter clade is the main group associated with microalgae and the dominant member of QS bacteria. The mechanisms of marine Roseobacter that regulating ecological function through QS and affect algae-bacteria interactions are still unknown. Some essential questions related to the response mechanism of microalgae host toward QS system and whether existing crosskindom singals between microalgae and bacteria are unclear. In this study, we aim to four marine Roseobacter strains that associated with microalgae and analyze their QS systems from molecular and gene levers. The luxI homologou gene deletion mutant is obtained by using CRISPR technique. Then, we verify the ecological functions regulated by QS and study the affectation of the functions to microalgae host. In the meantime, we also study the QS exit mechanism probably existing in phycosphere and investigate the driving factors. This study will deepen our knowledge of ecological functions regulated by QS in marine Roseobacter. The results will help us to comprehensively understand the generating and vanishing process of microalgae population, and the dynamic balance mechanism of phycosphere.

藻菌相互作用是藻际微环境保持生态平衡的重要因素，从化学生态学层面来认识藻菌作用关系已成为藻类生态学和微生态学研究的前沿和热点，而细菌群体感应（Quorum Sensing, QS）作为化学信号介导的调节方式备受关注。海洋玫瑰杆菌这一海洋微藻共栖细菌中的主体类群和QS细菌优势种，是如何通过QS调控生态学功能，进而影响藻菌作用关系的研究还未系统开展；藻菌间是否存在跨界信号传递，以及对QS的响应机制问题也有待解答。本项目在前期研究基础上，以海洋微藻共栖玫瑰杆菌为研究对象，从分子和基因水平解析存在的QS，应用CRISPR基因编辑新技术构建luxI同源基因缺失突变株，探明该类细菌QS调控功能及其对共栖藻的影响；同时，对藻际微环境中存在的群体感应退出机制进行研究，对退出的驱动因子进行解读。该研究不仅将加深对海洋玫瑰杆菌QS调控功能的探知，还有助于全面了解微藻种群生消过程及藻际微环境生态平衡的维持机制。

藻菌相互作用是藻际微环境保持生态平衡的重要因素，从化学生态学层面来认识藻菌作用关系已成为藻类生态学和微生态学研究的前沿和热点。随着群体感应（Quorum Sensing, QS）介导的藻菌关系被逐渐发掘，如能更为清楚的了解微藻共栖细菌QS的调控功能及作用方式，将为深入认识赤潮爆发过程中微藻优势种的演替及其生消过程提供更加充分的依据。本研究选择海洋玫瑰杆菌这一海洋微藻共栖细菌中的主体类群和QS细菌关键种类，从分子和基因水平解析存在的QS，探明该类细菌QS调控功能及其对共栖藻的影响；同时对藻际微环境中存在的QS退出机制进行解读。研究结果显示，从典型赤潮藻中分离出842株微藻共栖细菌，其中113株（13.42 %）为QS细菌。这些QS菌主要属于Sulfitobacter，Ponticoccus，Leisingera和Nitratireductor，且90%是玫瑰杆菌。它们具有成膜、降解DMSP和促进或抑制藻类生长的藻菌作用相关的生态学功能。对其中的Ponticoccus sp. PD-2和Sulfitobacter sp. H46进行了系统的藻菌作用关系研究。发现PD-2具有广谱性的抑藻能力，通过CRISPR基因编辑技术确定PD-2的QS可调控产生抑藻物质，且PD-2产生的酰化酶在生长后期降解了自身产生的AHLs信号分子，由此可以推断该菌具有主动的QS退出机制。H46对海洋卡盾藻生长具有显著的抑制作用，对硅藻表现出促生长作用。研究发现该菌产生耐热抑藻物质，特异性的抑制卡盾藻生长。同时H46可产生吲哚乙酸促进硅藻的生长，而硅藻产生的DMSP又为H46提供营养。这也是首次发现微藻共栖细菌和不同微藻存在差异性的藻菌作用关系，即维护具有互利关系微藻的生长，杀灭无利藻种。研究结果不仅加深我们对海洋玫瑰杆菌QS调控功能的探知，还有助于全面了解微藻种群生消过程及藻际微环境生态平衡的维持机制。