The cpsABCDE genes involved in polysaccharide production in Streptococcus salivarius ssp. thermophilus strain NCBF 2393.

A 4074-bp EcoRI fragment of Streptococcus salivarius ssp. thermophilus (S. thermophilus) chromosomal DNA containing genes involved in exocellular polysaccharide (EPS) was identified and cloned. The nucleotide sequence of this fragment was determined and found to contain one partial and four complete open reading frames. These were designated cpsA, cpsB, cpsC, cpsD and cpsE and encoded proteins of > 130, 243, 230, 246 and 455 amino acids, respectively, that showed homology with the genes of the cps cluster, involved in polysaccharide biosynthesis, in Streptococcus pneumoniae Type 19F. The cpsA gene is predicted to encode a transcriptional regulator, while cpsC and cpsD are predicted to encode proteins involved in polysaccharide polymerization and export. The cpsE gene is likely to encode the phosphate-prenyl glycosyl-1-phosphate transferase catalyzing the first step in polysaccharide biosynthesis in S. thermophilus. Southern blot analysis revealed that cpsE is found only in polysaccharide producing strains of S. thermophilus.