Enhanced β-glucan and pullulan production by Aureobasidium pullulans with zinc sulfate supplementation

The effects of mineral salts on the production of exopolysaccharides, including β-glucan and pullulan, by Aureobasidium pullulans CCTCC M 2012259 were investigated. Zinc sulfate at certain concentrations decreased dry biomass but favored to the biosynthesis of both exopolysaccharides. When 100 mg/L zinc sulfate was added to the fermentation medium, production of β-glucan and pullulan increased by 141.7 and 10.2%, respectively, when compared with that noted in the control without zinc sulfate addition. To reveal the physiological mechanism underlying improved β-glucan and pullulan production, key enzymes activities, energy metabolism substances, intracellular uridine diphosphate glucose (UDPG) levels, and gene expression were determined. The results indicated that zinc sulfate up-regulated the transcriptional levels of pgm1, ugp, fks, and kre6 genes, increased activities of key enzymes involved in the biosynthesis of UDPG, β-glucan and pullulan, enhanced intracellular UDPG content, and improved energy supply, all of which contributed to the increment in β-glucan and pullulan production. The present study not only provides a feasible approach to improve the production of exopolysaccharides but also contributes to better understanding of the physiological characteristics of A. pullulans.