Improved ammonia production from soybean residues by cell surface-displayed l-amino acid oxidase on yeast

Ammonia is critical for agricultural and chemical industries. The extracellular production of ammonia by yeast (Saccharomyces cerevisiae) using cell surface engineering can be efficient approach because yeast can avoid growth deficiencies caused by knockout of genes for ammonia assimilation. In this study, we produced ammonia outside the yeast cells by displaying an l-amino acid oxidase with a wide substrate specificity derived from Hebeloma cylindrosporum (HcLAAO) on yeast cell surfaces. The HcLAAO-displaying yeast successfully produced 12.6 mm ammonia from a mixture of 20 proteinogenic amino acids (the theoretical conversion efficiency was 63%). We also succeeded in producing ammonia from a food processing waste, soybean residues (okara) derived from tofu production. The conversion efficiency was 88.1%, a higher yield than reported in previous studies. Our study demonstrates that ammonia production outside of yeast cells is a promising strategy to utilize food processing wastes.

Automated summary

Producing ammonia outside of yeast cells through cell surface engineering is an efficient approach to avoid growth deficiencies caused by ammonia assimilation gene knockout. Displaying HcLAAO on yeast cell surfaces successfully produced ammonia with a conversion efficiency higher than previous studies. This study demonstrates the promising strategy of utilizing food processing wastes for ammonia production.