Impact of physical parameters on EPS production and gene expression in Ligilactobacillus salivarius KC27L and Limosilactobacillus reuteri KC21L strains.

Two lactic acid bacteria strains, Ligilactobacillus salivarius KC27L and Limosilactobacillus reuteri KC21L, were investigated for their ability to produce exopolysaccharides (EPS). The study evaluated the influence of different physical and nutritional factors, including carbon and nitrogen sources, pH, incubation time, temperature, and CO₂ concentration, to identify optimal conditions for EPS production. Under optimized conditions, L. salivarius KC27L reached 464 mg/L and L. reuteri KC21L achieved 433 mg/L, representing substantial increases compared to standard medium. A combined culture strategy, integrating sucrose as the primary carbon source and strain-specific nitrogen supplements, further enhanced yields and demonstrated the importance of tailored optimization. To gain molecular insight, expression levels of key EPS biosynthesis genes were examined under control versus optimized conditions. In L. salivarius KC27L, upregulation of the epsC gene was observed, suggesting its central role in enhanced EPS production, while other genes showed reduced expression. In L. reuteri KC21L, most analyzed genes were downregulated, indicating strain-specific regulatory mechanisms. Overall, the findings highlight the potential of optimization strategies to significantly enhance EPS yields in LAB strains. Moreover, the observed link between growth conditions and epsC expression provides a promising molecular target for improving EPS biosynthesis, supporting the industrial and biotechnological application of these strains.