Transcriptome analysis of Aureobasidium pullulans BL06 and identification of key factors affecting pullulan production

Pullulan, a versatile water-soluble polysaccharide, is widely used across various industries. To minimize byproduct interference, Aureobasidium pullulans BL06ΔPMAs was engineered, resulting in a higher yield and a lower molecular weight (MW) than the parent strain A. pullulans BL06. Comparative transcriptomic analysis revealed differentially expressed genes (DEGs) involved in sucrose metabolism, gluconeogenesis, glyoxylate metabolism, and amino acid metabolism. These DEGs may influence substrate consumption, energy production, and membrane composition, ultimately impacting pullulan synthesis. Additionally, further experimental validations were conducted on the genes with the most significant differential expression. Overexpressing glycosyltransferase gene (gta1, the third most differentially expressed gene) in A. pullulans BL06 increased pullulan production by 8.1 %, indicating its role in short α-1,4-glucan synthesis. Overexpression of the transmembrane transporter gene (st1, the most significantly differentially expressed gene) reduced pullulan molecular weight by 25 %, which potentially influences cell membrane fluidity and pullulan secretion. Furthermore, amylase (Amy1) was found to significantly impact molecular weight (MW) within the first 48 h of fermentation, an effect not previously reported for amylase, while its knockout resulted in a remarkable 7.6-fold increase in pullulan MW. These findings provide valuable insights for regulating pullulan yield and MW, offering innovative genetic targets for strains engineering in future industrial applications.