Transcriptomic Insights Into the Growth Phase- and Sugar-Associated Changes in the Exopolysaccharide Production of a High EPS-Producing Streptococcus thermophilus ASCC 1275

Abstract

In a previous study, incorporation of high exopolysaccharide (EPS) producing dairy starter bacterium Streptococcus thermophilus ASCC 1275 was found to improve functionality of low fat mozzarella cheese and yogurt. This bacterium in its eps gene cluster has a unique pair of chain length determining genes, epsC- epsD, when compared to other sequenced S. thermophilus strains. Hence, the aim of this study was to understand the regulatory mechanism of EPS production in this bacterium using transcriptomic analysis to provide opportunities to improve the yield of EPS. As sugars are considered as one of the major determinants of EPS production, after preliminary screening, we selected three sugars, glucose, sucrose and lactose to identify the EPS producing mechanism of this bacterium in M17 medium. Complete RNA-seq analysis was performed using Illumina HiSeq 2000 sequencing system on S. thermophilus 1275 grown in three different sugars at two-time points, 5 h (log phase) and 10 h (stationary phase) to recognize the genes involved in sugar uptake, UDP-sugar formation, EPS assembly and export of EPS outside the bacterial cell. S. thermophilus 1275 was found to produce high amount of EPS (∼430 mg/L) in sucrose (1%) supplemented M17 medium when compared to other two sugars. Differential gene expression analysis revealed the involvement of phosphoenolpyruvate phosphotransferase system (PEP-PTS) for glucose and sucrose uptake, and lacS gene for lactose uptake. The pathways for the formation of UDP-glucose and UDP-galactose were highly upregulated in all the three sugars. In the presence of sucrose, eps1C1D2C2D were found to be highly expressed which refers to high EPS production. Protein homology study suggested the presence of Wzx/Wzy-dependent EPS synthesis and transport pathway in this bacterium. KEGG pathway and COG functional enrichment analysis were also performed to support the result. This is the first report providing the transcriptomic insights into the EPS production mechanism of a common dairy bacterium, S. thermophilus.

Proteomic analysis reveals potential factors associated with enhanced EPS production in Streptococcus thermophilus ASCC 1275

“…The whole genome sequencing of S. thermophilus 1275 revealed that it has a unique set of chain length determining genes in its EPS gene cluster when compared with the other five fully sequenced S. thermophilus strains 10 . We have also observed that the sugar available in the media and growth phase influence the amount of EPS produced by S. thermophilus 1275 and the genes that lead to the production of EPS 13 . Another interesting feature of S. thermophilus 1275 is the presence of an effective proteolytic system with several intracellular peptidases and proteases 10 .…”

“…S. thermophilus 1275 was found to produce high amount of EPS in 1% sucrose supplemented medium when compared to lactose and glucose 13 . Hence, in this study, we investigated the proteome of high EPS producing dairy bacterium S. thermophilus 1275 and compared the proteomic level differences in this bacterium under the influence of three sugars, glucose, sucrose and lactose at two growth phases 5 h and 10 h. This is the first study providing insight into the proteomics of a high EPS producing lactic acid bacterium.…”

“…Based on our previous study, sucrose (1%) was found to produce more EPS in M17 medium (~430 mg/L) at stationary phase (12 h) when compared to glucose (~276 mg/L) and lactose (~163 mg/L) at the same concentration 13 . This significant variation in EPS production with different sugars motivated us to understand the changes at gene level that may be occurring in S. thermophilus 1275.…”

“…The transport of EPS from cytoplasm to the external environment can occur through various pathways. In S. thermophilus 1275 Wzy/Wzx pathway was found to be responsible for the transport of EPS based www.nature.com/scientificreports www.nature.com/scientificreports/ on the expression of genes 13 . However, in the proteomic study flippase (epsLM) and polymerase proteins (epsI) involved in Wzy/Wzx pathway were not included in the DEPs (Fig.…”

“…The study on the genomic insights of S. thermophilus 1275 provided a well-documented database for transcriptomics and proteomics analysis 10 . Moreover, our recent transcriptomics study on S. thermophilus 1275 under three different sugars and two growth phases provided information about the differentially expressed genes mainly related to EPS production 13 . In this study, the strain S. thermophilus 1275 was used to understand the global level proteomic changes influenced by three selected sugars (glucose, sucrose and lactose) and two growth phases (log phase, 5 h; stationary phase,10 h).…”