湿地固氮细菌驱动的碳氮固定及耦合机制

固氮细菌是地球上唯一能将氮气转化为化合态氮的生物，非光合固氮细菌通常被认为不具备固碳能力。有报道表明微生物或半导体矿物产生的胞外电子有可能被周围的微生物利用并影响它们的代谢。湿地底泥是微生物间以及微生物和矿物互作最为活跃的环境。申请人团队前期利用模拟胞外电子的体系研究湿地底泥微生物时发现光合与非光合固氮细菌均具有潜在固碳能力，而且胞外电子可能促进固氮。这暗示着固氮细菌具有一些尚未被完全认知的能量利用方式和固碳途径。基于此，本项目拟明确光合固氮菌胞外电子吸收传递途径及其激发的固氮作用，探究固碳与固氮系统间电子分配及相应协调机制；解析非光合固氮菌胞外电子吸收传递及其激发的固碳和固氮分子机制；估算水圈有氧环境固氮菌的碳氮固定量及贡献；最终解析固氮细菌吸收利用胞外电子固定碳氮的途径及相应耦合机制。研究有望揭示固氮菌新的能量利用方式及相应机制，实现科学目标：阐明水圈微生物驱动碳氮元素循环的机制。

Mineral-microbe interactions play an important role in biogeochemical cycles in earth. The sediment in wetland is the nature environments where microorganisms frequently interact each other and with minerals. Extracellular electron uptake (EEU) is the ability of microbes to take up electrons from solid phase conductive substances (SPCSs ) such as metal oxides. Recently, the phototrophic nitrogen-fixing bacterium Rhodopseudomonas palustris TIE-1 has been found to fix CO2 during EEU, yet it is not clear about whether TIE-1 can fix nitrogen to use SPCSs as electron donors. It has been reported that the metabolisms and growth of non-phototrophic bacteria can be stimulated by solar light through photocatalysis of semiconducting minerals. Our preliminary studies have suggested that the non-phototrophic nitrogen-fixing bacteria have ability to fix CO2 and/or N2 during EEU. Therefore, our overall objective is to elucidate the molecular mechanisms of EEU during nitrogen and/or carbon fixation by the nitrogen-fixing bacteria. This will lead to a deep understanding of the biogeochemical cycles in aquatic sediments and a better utilization of nitrogen-fixing bacteria. The specific aims for the proposed grant period are to:.1..By using phototrophic nitrogen-fixing bacterium R. palustris TIE-1 as a model organism, to determine the key proteins for EEU and whether TIE-1 can fix nitrogen by using SPCSs as electron donors and how the electrons are balanced between the carbon and nitrogen fixing systems..2..Define the ability of non-phototrophic nitrogen-fixing bacterium Azospirillum brasilense to fix CO2 and/or N2 during EEU and its associated molecular mechanisms..3..Investigate how bacteria achieve the carbon and nitrogen fixation by using SPCSs as electron donors under aerobic environment and evaluate the contribution of carbon and nitrogen fixation during EEU in wetland.