The reduction of chemically inert nitrogen to ammonia is a critical step in the global nitrogen cycle. Microbial nitrogen fixation is a promising way to realize nitrogen reduction and ammonia production at mild conditions. Here, we report an engineered, non-diazotrophic Synechococcus elongatus PCC 7942 strain with nitrogen fixation activity that is constructed by integrating a modified nitrogenase gene cluster into the genome. The engineered S. elongatus PCC 7942 strain is employed in a bioelectrochemical nitrogen-fixation (e-BNF) system for ammonia production. Because the e-BNF system supplies adequate external electrons for the turnover of nitrogenase, the nitrogen fixation activity of the engineered S. elongatus PCC 7942 strain is significantly improved. After 48 h of reaction, the e-BNF system accumulates 173 μM of NH₃, which is 21 times higher than that generated from solely photosynthesis-driven nitrogen fixation, with faradaic efficiency of 6.85%. This work may provide new insight into biological nitrogen-fixation systems and ammonium production.

将化学惰性氮还原为氨是全球氮循环中的关键步骤。微生物固氮是一种在温和条件下实现减氮产氨的有前景的方法。在这里，我们报告了通过将修饰的固氮酶基因簇整合到基因组中而构建的具有固氮活性的工程化、非固氮细长聚球藻PCC 7942 菌株。工程化的S. elongatus PCC 7942 菌株用于生物电化学固氮 (e-BNF) 系统以生产氨。因为 e-BNF 系统为固氮酶的转换提供了足够的外部电子，工程化的S. elongatus 的固氮活性PCC 7942 菌株得到显着改善。反应 48 小时后，e-BNF 系统积累了 173 μM 的 NH ₃，是光合作用驱动固氮的 21 倍，法拉第效率为 6.85%。这项工作可能为生物固氮系统和铵生产提供新的见解。