吲哚-3-乙酸介导地中海亚硫酸杆菌SC1-11在藻际环境定殖的机制研究

植物共生细菌分泌的吲哚-3-乙酸（IAA）对宿主的生长和防御反应以及细菌定殖发挥重要作用。亚硫酸杆菌是硅藻藻际环境中一类重要的共生细菌。已有研究表明，亚硫酸杆菌能够合成IAA并以此促进藻细胞的生长，但是IAA对细菌本身的作用和机制还未清晰。前期研究中，我们发现地中海亚硫酸杆菌SC1-11可能通过IAA介导的抗氧化胁迫机制应对宿主藻产生的氧化压力，从而适应藻际环境。基于此，本研究拟首先构建IAA缺陷型菌株，探究细菌内源IAA水平对其抗氧化能力的影响；然后借助组学技术和分子生物学手段，鉴定IAA介导的抗氧化应激途径及探究IAA关键调控蛋白的互作关系，从而揭示IAA介导的细菌抗氧化机制；最后通过检测共培养系统藻-菌的生理生化状态，明确IAA对细菌定殖藻际环境的影响。本研究结果预期能够揭示IAA在地中海亚硫酸杆菌SC1-11定殖藻际环境过程的作用和机制，为深入解析“藻-菌”共生互作提供科学依据。

Indole-3-acetic acid (IAA) secreted by plant symbiotic bacteria plays important roles in host growth and defense response as well as bacterial colonization. The genus Sulfitobacter is an important class of commensal bacteria inhabiting in diatom phycosphere. Previous studies suggested that Sulfitobacter spp. can synthesize IAA and then promote the growth of microalgal cells, but the role and mechanism of IAA action in bacteria are not clear. Previously, our founding revealed that Sulfitobacter mediterraneus SC1-11 can overcome the oxidative stress from phycosphere to survive and colonize by a cascade of IAA-mediated antioxidative responses. Based on this, this study is proposed to 1) construct a set of IAA-deficient strains for exploring the effects of bacterial endogenous IAA level on its antioxidation; 2) reveal a IAA-mediated antioxidative mechanism in Sulfitobacter mediterraneus SC1-11 by identifying the pathways related to antioxidative responses induced by IAA signaling and dissecting the interactions between IAA and key regulatory proteins; and 3) clarify the effects of IAA on bacterial colonization in phycosphere by determining the physiological and biochemical status of microalgae and bacteria in the co-culture system. This study will be expected to reveal the role and mechanism of IAA action in the process of colonization of Sulfitobacter mediterraneus SC1-11 in phycosphere, and provide a scientific basis for the further understanding of microalgae-bacterial interactions.