Engineering Cyanobacterium with Transmembrane Electron Transfer Ability for Bioelectrochemical Nitrogen Fixation

Abstract

Increasing attention has been paid to bioelectrochemical nitrogen fixation (e-BNF) as a promising approach to achieve the NH 3 synthesis under mild conditions. However, currently developed microbial e-BNF systems all rely on diffusible mediators to deliver redox equivalents inside the bacteria. Challenges of using diffusible mediators include toxicity, inefficient transmembrane diffusion, mediator inactivation, mediator contamination, and low energy efficiency. To date, e-BNF through transmembrane electron uptake without using diffusible electron mediators has not yet been reported. Herein, we describe a genetic strategy to engineer cyanobacterium Synechococcus elongatus PCC 7942 with transmembrane electron transfer (TET) ability to realize e-BNF without the addition of soluble mediators. The engineered S. elongatus PCC 7942 strain Se-nif with N 2 fixation activity was further transformed with an outer membrane protein cytochrome S OmcS, which contributes for the extracellular electron transfer (EET) ability of Geobacter sp. The engineered Senifom strain exhibited enhanced TET ability resulting in an approximately 13-fold higher NH 3 production rate than the corresponding Se-nif strain. The Faradaic efficiency of the Senifom e-BNF system was calculated to be approximately 23.3%, which is higher than the previously reported e-BNF systems. The electron pathway of the obtained extracellular electron was briefly analyzed and an extracellular electron uptake mechanism in the Senifom strain was proposed. This work demonstrates that a genetically engineered conduit can facilitate transmembrane electronic communication from the electrode to living cells, thereby providing insights into bioelectrosynthesis technology, especially the e-BNF systems and ammonium production.

A 300-fold conductivity increase in microbial cytochrome nanowires due to temperature-induced restructuring of hydrogen bonding networks

“…OmcS is essential for the reduction of iron oxides, an important electron acceptor in the native environment of G. sulfurreducens , as well during the early growth stages of electricity-producing biofilms in bioelectrochemical systems ( 49 ). In addition, artificially expressing cytochrome OmcS in photosynthetic cyanobacteria increased catalytic performance in a diversity of processes such as an increase in photocurrent by 9-fold ( 50 ), increased nitrogen fixation by 13-fold ( 51 ), and improved photosynthesis by increasing 60% biomass ( 52 ) compared to the wild-type cyanobacteria. These studies highlight the important role of OmcS in light-driven biocatalysis.…”

Bio-Inspired Redox-Adhesive Polydopamine Matrix for Intact Bacteria Biohybrid Photoanodes

“…Biohybrid electrochemical systems, where biological catalysts are coupled to abiotic electrodes, represent a sustainable approach for a variety of technological applications spanning from biosensing and water quality monitoring, − bioelectrosynthesis, − and micro to low power generation. − Additionally, the use of photosynthetic entities as the biocatalyst allows utilizing sunlight, one of the most attractive energy sources, to power such systems, paving the way to the field of semiartificial photosynthesis. − Using whole, metabolically active, microorganisms greatly simplifies the preparation of the biocatalyst (no enzyme isolation/purification required) and potentially enhances stability of the system thanks to their self-repairing and replication features. Purple nonsulfur bacteria have been used as model organisms for studying bacterial photosynthesis. , Additionally, purple bacteria are of great interest for their potential application for H 2 synthesis, , as well as bioremediation and biosensing, with Rhodobacter capsulatus ( R. capsulatus ), representing a very interesting candidate as biophoto­catalyst due to their extreme metabolic versatility .…”

Microbial biofilms as living photoconductors due to ultrafast electron transfer in cytochrome OmcS nanowires

“…In addition to light-induced whole-cell catalysis 21 , 26 , artificially expressing cytochrome OmcS in photosynthetic cyanobacteria, increased catalytic performance in diverse processes such as an increase in photocurrent by 9-fold 27 , increase in nitrogen fixation by 13-fold 28 , and improved photosynthesis due to 60% increase in biomass 29 compared to the wild-type cyanobacteria. These studies highlight the vital role of OmcS in light-driven biocatalysis.…”