胞外呼吸菌驱动沉积物-水界面光合细菌固碳的电子互营机制

Microbial phototrophs, contributing nearly 50% primary production to Earth, are the engine of Earth hydrosphere’s carbon cycling. Unlike oxygenic phototrophs (cyanobacteria), anoxygenic phototrophic bacteria (APB) do not generate oxygen during photosynthesis and their ecological importance has been long neglected. Light and electron donor are two indispensable factors for APB photosynthetic carbon fixation process. However, the lack of electron donors, like sulfide, is in conflict with the abundance of APB in natural water, especially in freshwater environment. The theory of interspecies electron transfer inspires us to explore the electron sources of APB during photosynthesis. Based on the “electron respiration” of extracellular respiration microbes and anoxygenic phototrophic bacteria, this project hypothesizes that extracellular respiration microbes drive APB to fix carbon via electric syntrophy. The energy transfer process of electron—>phototrophs + light—>organic carbon in the interface of sediments and water will be systematically investigated using freshwater wetland as research objective. Three kinds of electron transfer mechanism, including direct transfer, electron shuttle and conductive network, will be investigated to explain the coupling effect of microbial extracellular respiration and photosynthetic carbon fixation. It does not only help to deeply understand the anaerobic syntrophic process, but also widen the scientific implications of hydrosphere’s microbes in photosynthetic carbon fixation.

微生物光合作用承担了全球近50%的初级生产力，是地球水圈碳循环的引擎。与蓝细菌等产氧光合细菌不同，不产氧光合细菌（APB）光合过程不产生氧气，其生态重要性长期被忽视。APB的光合固碳过程需要“光照+电子供体”两个基本条件，但是自然水体（尤其是淡水环境）中硫化物等电子供体来源不足，难以解释APB高丰度生长的客观现象。种间电子传递理论的发现，为理解APB光合作用的电子来源提供了契机。本项目针对胞外呼吸菌与APB光合细菌厌氧“呼/吸”电子的特性，提出“胞外呼吸菌驱动光合细菌固碳的电子互营”假说。以淡水湿地为对象，系统研究沉积物-水界面胞外呼吸菌驱动“电子→光合细菌+光照→有机碳”的能量转移过程，解析胞外电子在微生物间“呼出与吸入”的直接传递、电子穿梭、导电物质介导机制，揭示新的微生物胞外呼吸—光合固碳耦合效应，为深入理解厌氧微生物互营代谢提供理论基础，有助于拓展水圈微生物光合固碳作用的科学内涵。

微生物光合作用承担了全球近50%的初级生产力，是地球水圈碳循环的引擎。与蓝细菌等产氧光合细菌不同，不产氧光合细菌（APB）光合过程不产生氧气，其生态重要性长期被忽视。APB的光合固碳过程需要“光照+电子供体”两个基本条件，但是自然水体（尤其是淡水环境）中硫化物等电子供体来源不足，难以解释APB高丰度生长的客观现象。种间电子传递理论的发现，为理解APB光合作用的电子来源提供了契机。本项目针对胞外呼吸菌与APB光合细菌厌氧“呼/吸”电子的特性，提出“胞外呼吸菌驱动光合细菌固碳的电子互营”假说。以淡水湿地为对象，系统研究了沉积物-水界面胞外呼吸菌驱动“电子→光合细菌+光照→有机碳”的能量转移过程，通过构建原位光电化学表征平台及双室光照微生物燃料电池系统，解析了胞外电子在微生物间“呼出与吸入”的直接传递、电子穿梭、导电物质介导机制，发现了核黄素、膜囊泡、鞭毛介导的胞外电子传递过程，提出了导电菌毛蛋白进化模型与依赖分子伴侣的组装模型，建立了核黄素介导的种间直接电子互营模型与依赖胞外细胞色素C的种间直接电子传递模型，揭示了种间电子传递群落具有氧化还原导电性，并进一步揭示了微生物胞外呼吸驱动的不产氧光合菌电能及光能固碳效应，为深入理解厌氧微生物互营代谢提供理论基础，并拓展了水圈微生物光合固碳作用的科学内涵。