Enhancing the Production and Monosaccharide Composition of Exopolysaccharides of Lactobacillus plantarum VAL6 by Applying Thermal Stress and Increased Carbon Dioxide Concentration

Abstract

Lactobacilli are able to produce exopolysaccharides (EPSs) with a wide diversity in structure and composition. However, changes in EPS production under environmental challenges are largely unknown. Here, to examine our hypothesis that EPS biosynthesis in lactobacilli is modulated by environmental conditions, we quantified and characterized the EPSs produced by Lactobacillus plantarum VAL6 following thermal stress and increased carbon dioxide (CO2) concentration. We found that the EPS yield and composition of L. plantarum strain VAL6 were markedly affected by these treatment conditions. The highest EPS yield reached 17.32 g/L under CO2 exposure, 2.2-fold higher compared to the control. The monosaccharide composition of synthesized EPSs was also altered when L. plantarum VAL6 was exposed to thermal stress and CO2 concentration increase. Whereas proportion of mannose was lower, glucose and galactose contents were higher than those in non-stressed variants. Both increased CO2 concentration and stress at 47°C enhanced the proportion of rhamnose in EPSs. Moreover, thermal stress and increased CO2 concentration triggered the expression of the genes involved in EPS biosynthesis, e.g., glmU, pgmB1, epsE, epsF, wzx, and wzy. Furthermore, the expression of epsE and epsF resulted in an increase in the content of galactose and glucose in EPS monosaccharide composition.