Microbial electrosynthetic nitrate reduction to ammonia by reversing the typical electron transfer pathway in Shewanella oneidensis

Ammonia production is a critical industrial process, and mild routes to recycle nitrates in wastewater could be a promising route to ammonia synthesis. In this study, ammonia production is demon-strated in a microbial electrosynthesis system with nitrate and an electrode as electron acceptors and donors, respectively. Based on the bidirectional extracellular electron transfer capability of She-wanella oneidensis MR-1, our microbial electrosynthetic system achieves a maximum ammonia production rate of 24.3 mg h-1$mg protein -1 with 82.5% selectivity and 33.1% cathodic efficiency and functions for several cycles over 30 days. Electrochemical analysis suggests that cytochromes c, flavins, and the flavin/c-cytochrome combination play a pivotal role. Charge transfer resistance weakens over the course of weeks, resulting in easier electron transfer. Paral-lel reaction monitoring proteomics suggest that reversing a typical Mtr pathwayplays a role, and a dissimilatory nitrate to ammonia pathway is used. This work proposes a progressive route to carry out ammonia synthesis under mild conditions.

Automated summary

Ammonia production is achieved in a microbial electrosynthesis system using nitrate and an electrode as electron acceptors and donors. With the help of She-wanella oneidensis MR-1, the system achieves a high ammonia production rate of 24.3 mg h-1$mg protein -1 with 82.5% selectivity and 33.1% cathodic efficiency. The electrochemical analysis indicates the important roles of cytochromes c, flavins, and the flavin/c-cytochrome combination. The work proposes a progressive route for ammonia synthesis under mild conditions.