藻类对促进海洋物质循环、维持水生环境的生态平衡具有重要作用。在藻菌关系中，基于微生物的多样性和重要性，藻菌之间的互作关系成为了研究的热点。藻际环境（Phycosphere）是藻菌共生的一种典型生态位（Niche），在这一微小生境中微生物形成的菌胶团（Zoogloea consortium）是调控藻菌关系的重要组成部分。以往的研究证明菌胶团具有结构多样性和功能多样性，在维持藻际环境稳定、物质循环和信息交流等方面具有重要的生态意义。菌胶团的形成过程受到多种因素的调控，其中群体感应信号（Quorum sensing，QS）分子作为一类化学信号扮演了至关重要的角色。作为一种细菌交流水平的通信机制，QS以密度依赖性方式调节基因表达并介导微生物的生理行为。以蓝藻（Cyanobacteria）为例，其藻际环境发现有多种QS分子的存在，它们在环境适应、物质交换和共生关系维持中扮演着重要的作用。然而，有关QS信号调控藻际菌胶团的研究却鲜有报道。为了评估群感信号对菌胶团的作用，我们以代表性的群体感应信号分子酰基高丝氨酸内酯类（N-acyl-homoserine lactone,AHL）信号为聚焦点，以铜绿微囊藻中分离的藻际细菌——新鞘氨醇杆菌Novosphingobium sp. ERN07为受试生物，评估AHL信号介导下细菌的成团机制。生化和遗传分析表明，细菌ERN07具有形成菌胶团的显著特性。该菌株具有一套LuxI/LuxR型的AHL系统，被编码为novI/novR，并表现出较高的产AHL的能力，主要合成3-OH-C8型的信号分子。QS基因敲除实验表明菌胶团的形成受AHL信号的正向调控。成团过程中ERN07能够增加胞外聚合物（Extracellular polymeric substances,EPS）的产生，改变EPS成分的组成比例，并显著影响微生物被膜（Biofilm）的形成（p<0.05）。为了探究菌胶团底物对藻的影响，将菌胶团底物添加到铜绿微囊藻的培养液中，观察到微藻的生长被显著促进。微藻的转录组学分析表明，菌胶团底物正向调节了微藻的光合效率和能量代谢过程。这些发现表明，新鞘氨醇杆菌ERN07菌胶团的形成受到AHL的介导，该成团行为在藻-菌相互作用关系中发挥了重要的生态作用，包括物质交换和共生关系的适应。本论文的结果能帮助我们更好地理解藻菌共生关系，为水华等生态事件的暴发或维持机制提供基于信号调控学说的理解。
Algae play an important role in promoting the circulation of marine materials and maintaining the ecological balance of the aquatic environment. In the relationship between algae and bacteria, based on the diversity and importance of microorganisms, the interaction between algae and bacteria has become a research hotspot. Phycosphere is a typical niche for the symbiosis of algae and bacteria, and the Zoogloea consortium formed by microorganisms in this micro-habitat is an important part of regulating the relationship between algae and bacteria. Previous studies have shown that bacterial aggregates have structural and functional diversity, and have important ecological significance in maintaining the stability of the phycosphere environment, material circulation and information exchange.The formation of microbial aggregate is regulated by many factors, among which quorum sensing （QS） molecules play a crucial role as a class of chemical signals. As a bacterial communication mechanism, QS regulates gene expression and mediates the physiological behavior of microorganisms in a density-dependent manner. Taking cyanobacteria as an example, a variety of QS molecules are found in the algal environment, and they play an important role in environmental adaptation, material exchange and symbiotic relationship maintenance. However, there are few reports on the regulation of QS signalling behaviors in phycosphere bacterial aggregation.To evaluate the role of quorum signaling on cell aggregation behavior, we focused on the representative QS signaling molecule, N-acyl homoserine lactone （AHL）, and using Novosphingobium sp. ERN07 as the test organism to evaluate the aggregation behavior and mechanism of bacteria mediated by AHL signal. Biochemical and genetic analyses revealed that ERN07 has the remarkable property of forming bacterial micelles. The strain has a set of LuxI/LuxR type AHL system, which is encoded as novI/novR, and shows a high ability to produce AHL, mainly synthesizing 3-OH-C8-HSL signal molecules. QS gene knockout experiments showed that the formation of bacterial aggregation was positively regulated by AHL signaling. During aggregation, ERN07 can increase the production of extracellular polymeric substances （EPS）, change the composition ratio of EPS components, and significantly affect the biofilm formation （p＜0.05）. In order to explore the effect of microbial aggregate substrate on algae, bacterial aggregate substrates were added to the culture solution of Microcystis aeruginosa, and it was observed that the growth of microalgae was significantly promoted. Transcriptomic analysis of microalgae revealed that bacterial aggregate substrates positively regulate the photosynthetic efficiency and energy metabolism process of microalgae. These findings suggest that AHL-mediated aggregation of ERN07 plays an important ecological role in algal-bacterial interactions, including material exchange and adaptation to symbiotic relationships. The results of this thesis contribute to a better understanding of algal-bacterial symbiosis, and provide an understanding based on the theory of signal regulation for the outbreak or maintenance mechanism of ecological events such as algal blooms.
