Genomic and phenotypic analyses of exopolysaccharide biosynthesis in Streptococcus thermophilus S-3

Abstract

Streptococcus thermophilus, one of the most important industrial lactic acid bacteria, is widely used as a starter culture in the dairy industry. Streptococcus thermophilus S-3 isolated from Chinese traditional dairy products has shown great potential for the production of larger amounts of exopolysaccharides (EPS), which significantly affect the organoleptic properties of fermented milk products. To understand the relationship between the genotype and phenotype of S. thermophilus S-3 in terms of EPS biosynthesis, its genome of strain S-3 was sequenced and the genes related to carbohydrate utilization, nucleotide sugars synthesis, and EPS biosynthesis were investigated. The genomic analysis revealed that S. thermophilus S-3 can use sucrose, mannose, glucose, galactose, and lactose. Phenotypic analysis showed that S-3 prefers fermenting lactose to fermenting glucose or galactose. The genetic analysis of nucleotide sugars and EPS biosynthesis revealed that S-3 can synthesize uridine diphosphate (UDP)glucose, deoxythymidine diphosphate-glucose, deoxythymidine diphosphate-rhamnose, UDP-galactose, UDP-N-acetylgalactosamine, and UDP-N-acetylglucosamine. A high yield of EPS from S-3 cultivated with lactose rather than glucose as the carbon source was correlated with high transcriptional levels of the genes associated with metabolism of these nucleotide sugars and EPS biosynthesis. Our results provide a better understanding of EPS biosynthesis in S. thermophilus and can facilitate enhanced EPS production by lactic acid bacteria fermentation via genetic and metabolic engineering approaches.

Comparative Genomics of Streptococcus thermophilus Support Important Traits Concerning the Evolution, Biology and Technological Properties of the Species

“…be useful for extrapolating findings from one strain to another. In all cases understanding of the EPS biosynthesis in S. thermophilus may allow a better selection of strains or even their engineering for improved dairy and probiotic products (Xiong et al, 2019a).…”

Exopolysaccharides From Streptococcus thermophilus ST538 Modulate the Antiviral Innate Immune Response in Porcine Intestinal Epitheliocytes

“…Structurally, the EPS produced by S. thermophilus are heteropolysaccharides made up of oligosaccharide repeating unit synthetized in the cytoplasm by the action of a number of glycosyltransferases and branched chains containing glucose and galactose, rhamnose and sometimes N-acetyl-glucosamine and fucose (Doco et al, 1990;Petit et al, 1991;Dan et al, 2009). Genome-scale studies revealed that the EPS biosynthetic pathway in S. thermophilus involves the sugar uptake system, nucleotide sugar synthesis, polysaccharide synthesis, and export of EPS, which are controlled by several housekeeping genes and a cluster of EPS-related genes (Laws et al, 2001;Wu et al, 2014;Cui et al, 2017;Alexandraki et al, 2019;Xiong et al, 2019). In lactic acid bacteria (LAB), the typical EPS gene cluster was described to contain five highly conserved genes epsA, epsB, epsC, epsD, and epsE, and a variable region, which includes the genes for polymerases, flippases, and a variable number of glycosyltransferases and other modifying enzymes [reviewed in Zeidan et al (2017)].…”

Genome Analysis and Physiological Characterization of Four Streptococcus thermophilus Strains Isolated From Chinese Traditional Fermented Milk

“…In the last two decades, a number of S. thermophilus genomes have been published, and the whole genome information has improved the understanding of metabolic activities of this bacterium at the molecular level, including the biosynthesis of EPS and folate (Iyer et al, 2010;Cui et al, 2017;Li et al, 2018;Xiong et al, 2019), resistance to bacteriophage (Hao et al, 2018), proteolytic system (Tian et al, 2018), and carbohydrate metabolism (Prajapati et al, 2013), etc. Furthermore, the comparative genomic analysis of different S. thermophilus strains with various technological properties has advanced the development of knowledge about the relationship between genetic characters and phenotypic traits (Rasmussen et al, 2008;Vendramin et al, 2017).…”