Improved Production and Rheological Properties of Exopolysaccharides by Co-Overexpression of β-1,3-Glucan Synthase and UDP-Glucose Pyrophosphorylase Genes in <i>Ganoderma lingzhi</i>

The β-1,3-glucan synthase gene 2 (<i>gls2</i>) from the biosynthetic pathway of polysaccharides was cloned and overexpressed in <i>G. lingzhi</i>. The content of intracellular polysaccharides in the <i>gls2</i> overexpression strain was 22.96 mg/100 mg of dry weight, 20% higher than that in the wild-type (WT) strain. The effect of co-overexpression of <i>gls2</i>, UDP-glucose pyrophosphorylase gene (<i>ugp</i>), and <i>gls</i> on polysaccharide biosynthesis was also investigated in <i>G. lingzhi</i>. The production of extracellular polysaccharides (EPS) in the G2-U-G transformants was 62% higher than that in the WT strain. Moreover, EPS from G2-U-G transformants had a higher molecular weight and glucose levels (6.3 × 10³ kDa and 89.19%) than those from the WT strain (4.8 × 10³ kDa and 78.15%), respectively. Furthermore, they showed higher viscosity, greater thixotropy, and a stronger gel network than EPS from the WT strain. Overall, this study contributes to the efficient production, development, and application of <i>Ganoderma</i> exopolysaccharides.