iTRAQ-based quantitative proteomic analysis of the global response in high EPS producing Streptococcus thermophilus ASCC 1275 in the presence of different sugars

Abstract

Exopolysaccharides (EPS) produced by LAB improve functional properties of fermented food. In our previous studies, Streptococcus thermophilus ASCC 1275 (ST1275) was found to produce high amount of EPS. We studied the influence of sugars (glucose, sucrose, and lactose) on the global proteomics of ST1275 to find the differentially expressed proteins (DEP) during EPS production. M17 medium was supplemented with 1% of each of the 3 sugars and ST1275 was grown at 37°C. The samples for proteomics analysis were collected at the log phase (5h) and stationary phase (10h). Isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analysis was conducted to identify the global protein responses of ST1275 under the influence of the 3 sugars. ProteinPilot software was used to validate MS/MS-based isobaric tag peptide for protein identification. Overall, 215, 474, 119 proteins were upregulated in the M17-glucose, M17-sucrose, and M17-lactose media, respectively. M17-sucrose medium, which showed high EPS production at 10h when compared with M17-glucose and M17-lactose media, had a significant upregulation of proteins involved in EPS assembly, phosphoenolpyruvate (PEP) transport system, methionine and cysteine/ arginine synthesis. Even though, in M17-lactose medium, at 5 h, there was a considerable upregulation of most of the proteins in nucleotide sugar synthesis and EPS assembly, the same level of expression was not observed at 10 h due to fast utilization of lactose in the medium and its unavailability thereafter. This study found that for high EPS production, the availability of sugars and the metabolic pathways that lead to EPS production should function in an organized manner.