Identification and expression profiling of exopolysaccharide gene cluster in Streptococcus thermophilus IMAU20246

Abstract:

[Objective] Streptococcus thermophilus IMAU20246 is a strain with good fermentation performance and high production of exopolysaccharides (EPS), while its gene cluster and pathway for EPS synthesis remain unclear. Therefore, whole-genome sequencing and bioinformatics tools can be employed to identify the gene cluster and decipher the mechanism of EPS synthesis. [Methods] The whole genome of S. thermophilus IMAU20246 was sequenced and bioinformatic analysis was performed to analyze the EPS biosynthesis-related gene clusters and pathway. Further, quantitative real-time PCR (qRT-PCR) was carried out to determine the expression levels of the EPS gene cluster at different time points. [Results] An EPS gene cluster of 18.1 kb was identified in the genome of S. thermophilus IMAU20246, including 15 genes. The strain synthesized 7 sugar nucleotides including UDP-glucose, dTDP-glucose, dTDP-rhamnose, UDP-galactose, UDP-galactofuranose, UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine by transporting glucose, mannose, fructose and galactose, lactose, trehalose, cellobiose, and sucrose, respectively. The results of qRT-PCR showed that the genes in the EPS gene cluster were expressed during the cell growth. In particular, the glycosyltransferase genes epsE, epsF, epsH, and epsJ reached the highest expression levels at the time point of 6 h, when the EPS yield peaked. [Conclusion] In this study, the gene cluster and pathway for EPS synthesis in S. thermophilus IMAU20246 were analyzed, which will provide a theoretical basis for further utilization of the strain.