Transcriptomics characterization of genes involved in exopolysaccharide production in Streptococcus thermophilus ASCC1275 under the influence of various sugars

Abstract

One of the major determinants of exopolysaccharide (EPS) production is the availability of carbohydrate in the growth media. In our previous study, it was observed that the model dairy starter bacterium Streptococcus thermophilus ASCC 1275 (ST1275) produces high amount of EPS. In the current work, we investigated the influence of 3 major sugars, glucose, sucrose and lactose on the global transcriptomics of ST1275, to examine the expression of genes involved in EPS production. The bacterium was grown in M17 media supplemented with 1% of each sugar at 37°C and samples were collected at log phase (5 h) and stationary phase (10 h) for transcriptomics study. Overall, 233, 520, and 408 genes were upregulated in glucose, sucrose and lactose supplemented media, respectively. It was observed that there was a significant upregulation of various genes involved in EPS assembly (epsA, eps B, eps 1C, eps 1D, eps O, eps P), arginine/cysteine and methionine synthesis and phosphoenolpyruvate (PEP) transport system (PTS) in sucrose supplemented medium, which showed high EPS production, when compared with lactose and glucose supplemented media at 10 h. Even though, there was a major upregulation of most of the genes in EPS gene cluster and nucleotide sugar synthesis in lactose medium at 5 h, the same level of expression was not observed at 10 h due to rapid utilization of lactose in the medium and its unavailability thereafter. This suggests the systematic involvement of different sugars and pathways for their metabolism for increasing the EPS yield.