There is a growing need to replace the Haber-Bosch process of converting nitrogen gas (N 2 ) into ammonia (NH 3 ) for fertilizers and fuels. To generate the 190 million tons of NH 3 each year through this process, roughly 2–3% of global energy is consumed and over 740 million tons of CO 2 released. Microbial processes may provide a low-energy and sustainable alternative. The nitrogenase enzymes in many free-living microorganisms convert N 2 into ammonium (NH 4 + ), generating fixed nitrogen for cellular growth. Attempts to increase NH 4 + yields from microorganisms through genetic engineering are seeing signs of success, but there is a lack of methods to increase NH 4 + generation rates. For aerobic microorganisms, providing sufficient oxygen gas as a terminal electron acceptor can increase these rates; however, oxygen gas can also shut down the nitrogenase enzyme. To overcome this limitation, we are exploring the ability of electricity to drive N 2 fixation in anaerobic, exoelectrogenic bacteria. These bacteria have the unique ability to respire on electrodes in microbial electrochemical technologies (METs). Applying a voltage to METs increases the respiration rates of exoelectrogens. Since the most abundant exoelectrogenic bacteria in METs are affiliated with the Geobacter genus and many known Geobacter species are N 2 fixers in soils and sediments, we hypothesized that 1) anode biofilms would exhibit N 2 fixation activity, 2) N 2 fixation rates would respond to an applied voltage, and 3) NH 3 could be generated by inhibiting NH 4 + uptake pathways. To test our hypothesis, we set up lab-scale microbial electrolysis cells (MECs) and promoted the growth of a Geobacter -rich anode biofilm using defined medium and operating conditions. We found that MET anode biofilms are capable of fixing N 2 while maintaining high current densities over several months. N 2 fixation rates increased more than three times to a max of 26 [nmol-ethylene (a proxy for N 2 fixation) / min] when the applied voltage increased from 0.7 V to 1.0 V. By adding an NH 4 + uptake inhibitor, NH 3 was generated and recovered from the MET. Using a pure culture of G. sulfurreducens , we also conducted transcriptomics under N 2 fixation conditions in METs operated at two different fixed anode potentials. This approach allowed us to identify what genes were up- and down-regulated under the two conditions. The presence of NH 4 + decreased the expression of genes associated with N 2 fixation which was expected due to the known sensitivity of nitrogenases to NH 4 + . On the other hand, the two anode potentials had a dramatic and unexpected impact on the expression levels of N 2 fixation genes. At the low anode potential [−0.15 V vs. standard hydrogen electrode (SHE)], nitrogenase genes were significantly up-regulated, as were genes associated with NH 4 + uptake and transport, such as glutamine and glutamate synthetases. Considering that −0.15 V provides less energy to the cells relative to +0.15 V (based on thermodynamic predictions), the results suggest that the cells responded to this highly energy-constrained environment by increasing expression of N 2 fixation pathways. Based on our new knowledge of how G. sulfurreducens regulates N 2 fixation and NH 4 + production, we are currently developing new strains of G. sulfurreducens using the CRISPR platform that can excrete NH 4 + during N 2 fixation.