High Glucose Is a Stimulation Signal of the Salt–Tolerant Yeast Zygosaccharomyces rouxii on Thermoadaptive Growth

Abstract

The salt–tolerant yeast Zygosaccharomyces rouxii is a typical aroma–producing yeast used in food brewing, but its mechanism of high temperature tolerance is still unclear. In this study, the response mechanism of Z. rouxii to glucose under high temperature stress at 40 °C was explored, based on the total synthetic lowest–nutrient medium. The results of the growth curves and scanning electron microscopy showed that high glucose was necessary for Z. rouxii to restore growth under high temperature stress, with the biomass at 300 g/L of glucose (OD600, 120h = 2.44 ± 0.26) being 8.71 times higher than that at 20 g/L (OD600, 120h = 0.28 ± 0.08). The results of the transcriptome analysis, combined with RT–qPCR, showed that the KEGG analysis of differentially expressed genes was enriched in pathways related to glucose metabolism, and high glucose (300 g/L) could effectively stimulate the gene expression of glucose transporters, trehalose synthesis pathways, and xylitol synthesis pathways under a high temperature, especially the expression of the glucose receptor gene RGT2 (up–regulated 193.7 times at 12 h). The corresponding metabolic characteristics showed that the contents of intracellular metabolites, such as glucose (Cmax, 6h = 6.50 ± 0.12 mg/g DCW), trehalose (Cmax, 8h = 369.00 ± 17.82 μg/g DCW), xylitol (Cmax, 8h = 1.79 ± 0.27 mg/g DCW), and glycerol (Cmax, 8h = 268.10 ± 44.49 μg/g DCW), also increased with time. The accumulation of acetic acid, as the main product of overflow metabolism under high temperature stress (intracellular Cmax, 2h = 126.30 ± 10.96 μg/g DCW; extracellular Cmax, 12h = 499.63 ± 27.16 mg/L), indicated that the downstream glycolysis pathway was active. Compared with the normal physiological concentration of glucose, a high glucose concentration can effectively stimulate the gene expression and metabolism of salt–tolerant Z. rouxii under high–temperature conditions to restore growth. This study helps to deepen the current understanding of the thermoadaptive growth mechanism of salt–tolerant Z. rouxii.