Adaptive Laboratory Evolution and Carbon/Nitrogen Imbalance Promote High-Yield Ammonia Release in Saccharomyces cerevisiae

Ammonia is one of the primary chemical commodities produced and is widely used as a fertilizer, with increasing interest as an energy storage vector. The primary method for producing ammonia today, the Haber-Bosch process, requires large amounts of energy and resources. Microbial production of ammonia is being developed and could provide more sustainable alternatives. No success has been achieved in using natural yeast cells. This paper reports that growing different Saccharomyces cerevisiae strains in a carbon/nitrogen unbalanced rich-protein medium results in limited ammonia secretion. Through adaptive laboratory evolution of the CEN.PK 113-7D strain, we selected an evolved strain with a 5-fold increase in ammonia excretion and amino acid utilization. Multi-step bioreactor fermentation of the evolved strain allowed the production of 1,36 g/L of ammonia, a value in line with levels produced by other microbial systems. This proof-of-concept study suggests that yeast-based processes can be adapted straightforwardly to ammonia production from high-protein-waste derived from several sources.