Comparative genomics among dairy strains of Streptococcus thermophilus

Microorganisms like lactic acid bacteria are employed for the biotransformation of raw materials into fermented foods. Fermented foods have increased nutritional value and shelf life as well as improved organoleptic characteristics compared to the raw materials. Interestingly, there are several genera within lactic acid bacteria that are considered to be important for food fermentations including the Streptococcus genus. However, only Streptococcus thermophilus is used as a starter culture. Streptococcus thermophilus has been adapted to milk and dairy products through a reductive evolution process that has led to the loss of typical streptococcal pathogenictraits. In this work we present the comparative genomic analysis among the recently sequenced genome of S. thermophilus ACA-DC 29 is olated from yogurt and the existing seven complete genome sequences of S. thermophilus. Full chromosome alignments revealed a high degree of synteny among the different strains although strain specific differences could also be observed. The pangenome of the eight strains was comprised of approximately 2,300 genes. Concerning the ACA-DC 29 strain, the majority of genes was distributed in the core and the accessory genomes. We also identified a significant percentage of unique genes, i.e. approximately 250, involved in various biological processes. Further analysis of these unique genes revealed that several of them may have been acquired through horizontal gene transfer. We also predicted five potential antimicrobial peptides and two CRISPR systems, which may confer resistance against phages. Overall, our analysis provides useful insights into the technological potential of the ACA-DC 29 strain