Abstract
Exopolysaccharide (EPS) produced from dairy bacteria improves texture and functionalities of fermented dairy foods. Our previous study showed improved EPS production from Streptococcus thermophilus ASCC1275 (ST1275) by simple alteration of fermentation conditions such as pH decrease (pH 6.5 → pH 5.5), temperature increase (37°C → 40°C) and/or whey protein isolate (WPI) supplementation. The iTRAQ-based proteomics in combination with transcriptomics were applied to understand cellular protein expression in ST1275 in response to above shifts during milk fermentation. The pH decrease induced the most differentially expressed proteins (DEPs) that are involved in cellular metabolic responses including glutamate catabolism, arginine biosynthesis, cysteine catabolism, purine metabolism, lactose uptake, and fatty acid biosynthesis. Temperature increase and WPI supplementation did not induce much changes in global protein express profiles of ST1275 between comparisons of pH 5.5 conditions. Comparative proteomic analyses from pairwise comparisons demonstrated enhanced glutamate catabolism and purine metabolism under pH 5.5 conditions (Cd2, Cd3, and Cd4) compared to that of pH 6.5 condition (Cd1). Concordance analysis for differential expressed genes (DEGs) and DEPs highlighted down-regulated glutamate catabolism and up-regulated arginine biosynthesis in pH 5.5 conditions. Down regulation of glutamate catabolism was also confirmed by pathway enrichment analysis. Down-regulation of EpsB involved in EPS assembly was observed at both mRNA and protein level in pH 5.5 conditions compared to that in pH 6.5 condition. Medium pH decreased to mild acidic level induced cellular changes associated with glutamate catabolism, arginine biosynthesis and regulation of EPS assembly in ST1275.
Highlights
Exopolysaccharide (EPS) produced by food-grade bacteria such as lactic acid bacteria (LAB) and bifidobacteria improves texture and functionality of fermented foods due to its stabilizing/texturizing properties as well as modulation of immune responses (Ruas-Madiedo et al, 2002; Welman and Maddox, 2003; Galle and Arendt, 2014; Multi-Omics of Streptococcus thermophilus in MilkHidalgo-Cantabrana et al, 2014)
We found the potential metabolism of glycogen/starch by ST1275 during our genomic study (Wu et al, 2014); our growth fermentation conducted for ST1275 (Supplementary Figure S1) did not show strong evidence for the metabolism of starch and
We found five differentially expressed proteins for purine metabolism were down-regulated at least by 2-fold suggesting the nucleotide synthesis was affected by decreasing the medium pH; most of DEPs linked to the category of translation, ribosomal structure and biogenesis were down regulated indicating potential shift of cellular translational event
Summary
Exopolysaccharide (EPS) produced by food-grade bacteria such as lactic acid bacteria (LAB) and bifidobacteria improves texture and functionality of fermented foods due to its stabilizing/texturizing properties as well as modulation of immune responses Str. thermophilus ASCC 1275 (ST1275), a conventional dairy starter, has been identified in our previous study as a high EPS producer in milk, and its EPS production could be improved by adjusting the fermentation conditions such as pH, temperature or supplementing milk with limited amount of whey protein isolate (WPI), a by-product from the cheese-making (Zisu and Shah, 2003). Due to the importance of Str. thermophilus in dairy industry (Iyer et al, 2010), ST1275 was used as a model high EPS-producing strain in this study to understand the role of environmental conditions in shaping its protein expression. We applied the iTRAQ-based proteomics approach (Figure 1) to detect the protein expression of ST1275 in response to pH 5.5 conditions; further paired analysis of differentially expressed proteins (DEPs) based on proteome data and DEGs based on our previous transcriptome data (Wu and Shah, 2018) for matched samples was performed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
