Engineering UDP-sugar synthesis pathways for exopolysaccharide biosynthesis in Streptococcus thermophilus AR333

Exopolysaccharide (EPS) produced by Streptococcus thermophilus can significantly improve the viscosity, texture and taste of dairy products, which have broad application potential in the food industry. However, EPS production is typically low (< 100 mg L^-1) in S. thermophilus, making it difficult to meet industrialization requirements. The utilization of metabolic engineering for genetic modification of S. thermophilus is an efficient approach to enhance EPS biosynthesis.

To our knowledge, there is lack of systematic investigation on engineering UDP-sugar synthetic pathways for EPS production in S. thermophilus. In the present study, the biosynthetic genes of EPS precursors UDP-glucose and UDP-galactose were regulated for improving EPS production in S. thermophilus AR333. Compared with the control, engineered strains by single overexpression of eight EPS precursor genes increased EPS production by 7-31%, respectively. Among of them, overexpressing glk encoding glucokinase and galE1 encoding UDP-galactose-4-epimase led to 275.37 and 288.65 mg L^-1 of EPS production, respectively. Moreover, co-overexpression of lacZ encoding β-galactosidase and galE1 achieved a remarkable 49% increase in the EPS production (329.51 mg L^-1). Transcriptional analysis further suggested that enhanced EPS synthesis in engineered strain can attributed to the upregulation of precursor genes and clusters of EPS genes.

Our results showed that engineered UDP-sugar synthesis is an efficient strategy to boost EPS production in S. thermophilus. © 2025 Society of Chemical Industry.