Effect of Glucose on Vanillin Tolerance of Starmerella bacillaris

This study focused on the effect of a typical phenolic inhibitor, vanillin, on the growth and ethanol production of Starmerella bacillaris R5, as well as the effect of varying levels of glucose on its growth and fermentation performance. The results indicated that when the vanillin concentration was fixed at 3 g/L, increasing glucose concentration in the medium from 2% to 6% shorten the lag phage by 25.92%, increased the specific growth rate by 82.1%, and the ethanol conversion rate by 17.88%. Further analysis showed that increased glucose concentration resulted in an increase in the proportion of cells containing reactive oxygen species (ROS), a decrease in membrane permeability, and a reduction in intracellular H2O2 content. In addition, the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) increased by 58%, 35.5%, and 2.3 times, respectively. Intracellular glycerol content increased by 1.82 times. The activity of pyruvate kinase (PK), related to glucose metabolism, decreased by 54.5%, and the activity of hexokinase (HK) and 6-phosphate glucose dehydrogenase (6-PGDH) increased by 4.16 and 11.8 times, respectively. The content of reduced nicotinamide adenine dinucleotide phosphate (NADPH) increased by 19.4%. The gene expression levels of hexokinase (HK), 6-phosphate fructose kinase (PFK), isocitrate dehydrogenase (IDH3), 6-phosphate glucose dehydrogenase (PGD), ethanol dehydrogenase (ADH5), pyruvate decarboxylase (PDC) and glycerol dehydrogenase 1 (GCY1) were up-regulated by 4.6, 2.5, 13.9, 12.2, 17.5, 34.8, and 34.9 times, respectively. In summary, increasing glucose concentration increased the activity of intracellular antioxidant enzymes, attenuated oxidative damage, and provided more adenosine triphosphate (ATP) and reducing powder to cope with environmental stress, thereby increasing the conversion rate of ethanol. The results of this study could provide new ideas for utilizing S. bacillaris for bioethanol production.