Exploring the high urea metabolic capacity of indigenous Schizosaccharomyces japonicus during alcoholic fermentation

Urea degradation by urease represents a promising green strategy for reducing ethyl carbamate in alcoholic beverages. This study characterized the urea metabolism capacity of indigenous Schizosaccharomyces japonicus, with strains FBKL2.9SZJ3 and FBKL2.9792 exhibiting robust urease activities (1.20 and 1.26 U/mL). They degraded over 95% of urea during alcoholic fermentation with initial levels of 1.5-6.0 g/L. Although the highest urease activity was induced in the simulated fermentation with initial urea level of 20 g/L, the formation of ethanol was restrained. Interestingly, the restrain was relieved by shift from the formation of glycerol to ethanol when the initial urea level of 1.5 g/L was raised to 20 g/L on the fourth day of fermentations. Arginine supplementation at the range of 0.5-1.5 g/L did not induce urease activity but increased urea production, and high-urease strains kept significantly lower urea levels than the low-urease strains. RT-qPCR analysis revealed distinct transcriptional responses among strains. Urea supplementation induced early and sustained upregulation of Ure2 and Ureatrans in high-urease strains, whereas UREG was upregulated only at the late stage. In contrast, low-urease strains showed late-stage upregulation of Ureatrans, with no significant induced transcription of Ure2 by urea supplementation. Urease activity was positively correlated with Ure2 (r = 0.7737, p < 0.001) and Ureatrans (r = 0.4861, p < 0.01), and moderately negatively correlated with UREG (r = -0.3251, p < 0.05). These findings provide references for further probing the urea metabolism pathway of S. japonicus, and for the application of high-urease strains to reduce urea and further control EC in fermented beverages.