Metabolic flux and transcriptome analyses provide insights into the mechanism underlying zinc sulfate improved β-1,3-D-glucan production by Aureobasidium pullulans

The effects of zinc sulfate at various concentrations on β-1,3-D-glucan (β-glucan) and pullulan production were investigated in flasks, and 0.1 g/L zinc sulfate was found to be the optimum concentration favoring increased β-glucan production. When batch culture of Aureobasidium pullulans CCTCC M 2012259 with 0.1 g/L zinc sulfate was carried out, the maximum dry biomass decreased by 16.9% while β-glucan production significantly increased by 120.5%, compared to results obtained from the control without zinc sulfate addition. To reveal the mechanism underlying zinc sulfate improved β-glucan production, both metabolic flux analysis and RNA-seq analysis were performed. The results indicated that zinc sulfate decreased carbon flux towards biomass formation and ATP supply, down-regulated genes associated with membrane part and cellular components organization, leading to a decrease in dry cell weight. However, zinc sulfate increased metabolic flux towards β-glucan biosynthesis, up-regulated genes related to glycan biosynthesis and nucleotide metabolism, resulting in improved β-glucan production. This study provides insights into the changes in the metabolism of A. pullulans in response to zinc sulfate, and can serve as a valuable reference of genetic information for improving the production of polysaccharides through metabolic engineering.