Mechanisms of exopolysaccharide synthesis by Streptococcus thermophilus IMAU20246 determined by the carbon source.

Our study characterized exopolysaccharide production by Streptococcus thermophilus IMAU20246 with lactose, glucose, galactose, or sucrose as sole carbon sources, and conducted comparative transcriptomics to unravel EPS synthesis mechanisms. The yield, molecular weight, monosaccharide composition and structure of EPSs were significantly affected by carbon sources. The yield of EPSs was highest (617 ± 5.9 mg/L), and Mw the smallest (3.789 × 10 Da) in sucrose; it was 1.5, 1.2 and 1.8 times higher than with lactose, glucose and galactose, respectively. Transcriptomic analysis identified 21 key enzymes for EPS synthesis, and S. thermophilus IMAU20246 preferentially regulated sucrose utilization through ABC transporters, phosphotransferase system (PTS), amino sugar and nucleotide sugar metabolism; and upregulated expression of EPS biosynthesis genes to increase EPS production. This study provides a theoretical basis for enhancing EPS content and reveals the dynamics of EPS synthesis in S. thermophilus which may be significant for further EPS production and application.