EPS phenotype and genotype in Streptococcus thermophilus strains of dairy origin

The aim of this work was to evaluate EPS production and the organisation of the eps gene cluster in 43 Streptococcus thermophilus strains of dairy origin. The EPS production was evaluated in M17 medium using glucose or lactose as the carbon source and the total sugar content was determined using the phenol-sulphate method. The amount of EPS produced using glucose as the carbon source ranged between 24 and 662 mg 1(-1) (glucose equivalents) and between 16 and 570 mg 1(-1) using lactose. PCR experiments showed that epsA, epsB, epsC, epsD, epsE and epsF genes were the most conserved and widespread in the exopolysaccharide locus, while few PCR positive signals were detected for epsG, epsH, epsJ and epsK genes. Results from the PCR cluster analysis allowed the identification of seventeen genotypes among the 44 analysed strains. The genetic polymorphism of the eps locus was further demonstrated by sequencing the epsCD genes of some representative strains. The EPS phenotype is widely distributed among S. thermophilus strains, but only few strains produce an amount of EPS of potential industrial interest. The spreading of the eps genes could be used as a genetic tool for S. thermophilus strains typing since, in some cases, the genotype was related to EPS production. The characterisation of the EPS phenotype and genotype of S. thermophilus strains should expand the knowledge of this biotechnological feature and help in the genetic characterisation of strains of potential industrial interest.