Abstract: The purpose of this study was to explore the biosynthesis pathway of exopolysaccharides (EPS) in Streptococcus thermophilus KLDS3.1012 at the molecular level and to verify it by the phenotypic traits. Firstly, genomic sequencing was performed using Illumina HiSeq and MiSeq sequencing platforms and a circular genomic map was skeletonized; subsequently, glycometabolism, sugar nucleotides synthesis and EPS gene clusters were analyzed by bioinformatics; finally, carbohydrate utilization was measured by API 50CH and the monosaccharide composition of the EPS produced by S. thermophilus KLDS3.1012 was analyzed using high performance anion exchange chromatography (HPAEC). In silico bioinformatic analysis unveiled that the genome of S. thermophilus KLDS3.1012 was related to sucrose, fructose, mannose, glucose, galactose and lactose uptake system, and biosynthesis of four sugar nucleotides (UDP-gluctose, dTDPrhamnose, UDP-galactose and UDP-N-acetylglucosamine) as well as an EPS gene cluster. The phenotypic traits revealed that S. thermophilus KLDS3.1012 could utilize these six sugars and the EPS produced it was composed of glucose, rhamnose and galactose. These results provide a theoretical basis for better understanding the relationship between the genetic elements and the structure of EPS in S. thermophilus KLDS3.1012 and for facilitating its potential applications as starter culture in the dairy industry.

Key words: Streptococcus thermophilus, genomic sequencing, bioinformatic analysis, glycometabolism, exopolysaccharides