自然界中各元素的生物地球化学循环并非孤立存在，而是与其它元素循环相互耦合并且相互推动。作为地球上最耗能的生化反应之一，生物固氮所需的能量和电子主要来源于有机碳氧化和光合作用；尽管全基因组分析表明一些化能硫氧化细菌也含有完整的固氮酶基因，但只有极少数菌株被报道在微氧条件下具有固氮能力。我们从珠江水体中分离的一株化能自养硫氧化细菌Halothiobacillus sp. LS2，不仅基因组中含有完整固氮酶基因，还能在有氧和厌氧条件下进行固氮作用，预示着一种硫氧化–固氮耦合的生化反应。本项目将通过化能自养硫氧化细菌驱动的硫氧化－固氮反应的耦合机制、调控策略、生态效应等研究，揭示一种新的微生物介导的N–S耦合生物地球化学循环过程，并探讨该过程在水圈中存在的普遍性。本项目对丰富水圈中元素的生物地球化学循环理论、推动水环境治理和水圈生态保护、开拓新的研究领域等有重要意义。

The biogeochemical cycles of each element in the nature are not exist solely, but coupled with other elements and pushed together. As one of the most energy-demanding bioreaction, the biological nitrogen fixation demanded energy and electron come mainly from organic carbon oxidation or photosynthesis. Though some chemotrophic sulfur-oxidizing bacteria have been found to own complete nitrogenase genes in their genomes, only a few strains have been reported to be able to fix nitrogen under microaerobic conditions. Chemoautotrophic sulfur-oxidizing bacterium Halothiobacillus sp. LS2 that we isolated from Pearl River water not only owns a complete nif regulon in genome but also is capable of fixing nitrogen under aerobic and anaerobic conditions, suggesting a coupling bioreaction between sulfur oxidation and nitrogen fixation. In this project, we will study the driving mechanisms, regulating strategies and ecological effects of the coupled bioreaction that mediated by chemoautotrophic sulfur-oxidizing bacteria. Based on these studies, we will reveal a new microbial-mediated process of N-S coupled biogeochemical cycle and discover the prevalence of this process in hydrosphere. This study is very meaningful for enriching the theory of element biogeochemical cycles in hydrosphere, promoting the water environment management and hydrosphere protection, and developing new research fields.