Assessment of the safety and metabolism characteristics of Streptococcus thermophilus DMST-H2 based on complete genome and phenotype analysis

A genome-based systematic analysis combined with phenotypic experiments was conducted to evaluate the safety properties and metabolic characteristics of Streptococcus thermophilus DMST-H2, isolated from Chinese traditional homemade yogurt in Inner Mongolia. Comparative genomic analysis showed that DMST-H2 had a closer genetic relationship with S. thermophilus KLDS.3.1003 based on the sequence similarities of the 1193 coregenes. No genes related to antibiotic resistance and virulence factor as well as no complete biogenic amine biosynthesis gene clusters were identified in DMST-H2 genome. DMST-H2 was sensitive to various antibiotics and had no hemolytic activity and no biogenic amine production capacity, confirming that DMST-H2 is safe and non-toxic. In addition, multiple genes for carbohydrate metabolism were predicted, including various carbohydrate-active enzymes and sugar transporters that could be involved in the transport of multiple carbon sources. Two exopolysaccharide (EPS) gene clusters (eps-1 and rgp-2) were also detected, indicating that DMSTH2 has the potential to synthesize heteropolysaccharides. Gene functional features revealed a cyclic antimicrobial peptide related gene cluster in DMST-H2, which displayed high identities with the streptide biosynthesis gene cluster as previously reported. Our comprehensive analysis of the whole genome and corresponding phenotypes of S. thermophilus DMST-H2 provides important theoretical basis for its application in food products.