Abstract: The purpose of this study was to gain genomic insights into the proteolysis system and amino acid biosynthesis in Streptococcus thermophilus KLDS SM. Firstly, whole genome sequencing was performed using combination of Illumina Hiseq 2500 sequencing and Pacific Biosciences RSII sequencing and the circular genomic map was constructed; subsequently, in silico bioinformatics analysis was carried out with respect to extracellular proteinase, peptide transport system, intracellular peptidase and amino acid biosynthesis; finally, comparative genomics of amino acid biosynthesis between strain KLDS SM and 14 other S. thermophilus strains, all of which have had the whole genome sequenced, was performed. The results showed that the genome of S. thermophilus KLDS SM consisted of a circular chromosome (1 856 787 bp) with GC content of 39.08%. A total of 1 732 protein-encoding genes were predicted. S. thermophilus KLDS SM had a complete proteolytic system and could biosynthesize eight amino acids. Furthermore, comparative genomics analysis showed that the amino acid biosynthesis abilities of 15 strains were relatively conservative except for a large difference in histidine biosynthesis among different strains. The results of this study can provide a theoretical basis for better understanding of nitrogen metabolism in S. thermophilus KLDS SM and are of important significance to exploiting it as a starter culture.

Key words: Streptococcus thermophilus, genome, bioinformatic analysis, proteolysis, amino acid biosynthesis