Optimizing Ammonia Quantification for Sustainable Microbial Ammonia Synthesis
Ammonia production accounts for nearly 2% of global energy consumption, motivating the search for sustainable biological alternatives to the energy intensive Haber Bosch process. Geobacter sulfurreducens is a promising microbial chassis for renewable ammonia synthesis due to its ability to fix atmospheric nitrogen through the nitrogenase enzyme under anaerobic conditions. To evaluate engineered strains designed to improve ammonia output, a reliable and safe quantification method is essential. The method previously used in our lab, Nessler’s reagent, is mercury-based and poses significant safety and scalability concerns.
This project aimed to develop and optimize a safer colorimetric assay using the salicylate method for accurate ammonia measurement in Geobacter cultures. A protocol was established and calibrated using 0–5 mM NH₄Cl standards, yielding a functional detection range of approximately 0.05–1.5 mM. The assay exhibited strong sensitivity within the low-millimolar concentrations typical of microbial nitrogen fixation studies.
Using the optimized method, baseline ammonia depletion by wild-type Geobacter was measured across varying starting concentrations. Wild-type cultures consistently depleted approximately 2.5 mM ammonia, establishing a quantitative baseline for comparison with engineered strains.
This work provides a safe, reliable, and scalable ammonia quantification method suitable for microbial electrochemical systems. Future efforts will apply this assay to engineered strains and refine the protocol for metal-rich media formulations used in strain development.