LAUSR

BACKGROUND Food grade-Streptococcus thermophilus produces biological exopolysaccharides (EPSs) with great potentials catering for higher health-promoting demands, however, how S. thermophilus regulates the biosynthesis of EPS is unelaborate, decelerating the application of these polymers. In our previous study, maltose, soy peptone and initial pH were three key factors of enhancing EPS yield in S. thermophilus CS6. Therefore, we aim to study the regulating mechanisms of EPS biosynthesis in S. thermophilus CS6 in the method of comparative transcriptome and differential carbohydrate metabolisms. RESULTS Soy peptone addition (58.6 g·L-1 ) and moderate pH (6.5) contributed to high bacterial biomass and high EPS yield (407 mg·L-1 ). Maltose, soy peptone and initial pH greatly influenced lactose utilization in CS6. Soy peptone addition induced high accumulation of mannose and arabinose in intracellular CS6, differential monosaccharide composition (mannose, glucose and arabinose) in EPS and high radical (DPPH, superoxide and ABTS) scavenging activities. Carbohydrate transportation, sugar activation and eps cluster-associated genes were differentially expressed to regulate EPS biosynthesis. Correlation analysis indicated high production of EPSs depended on high expression of lacS, galPMKUTE, pgm, gt2-5&4-1, and epsLM. CONCLUSION The production of antioxidant EPS in S. thermophilus CS6 depended on the regulations of galactose metabolism cluster and eps cluster. This study recommends a new approach to enhance EPS production by transcriptomic regulation for further food and health application of EPS. This article is protected by copyright. All rights reserved.