Abstract
To investigate the effect of environmental stresses on the exopolysaccharide biosynthesis, after 24 h of culture at 37 °C with pH 6.8 and without sodium chloride, Lactobacillus plantarum VAL6 was exposed to different stress conditions, including pH (pHs of 3 and 8) and high sodium chloride concentration treatments. The results found that Lactobacillus plantarum VAL6 exposed to stress at pH 3 for 3 h gives the highest exopolysaccharide yield (50.44 g/L) which is 6.4 fold higher than non-stress. Under pH and sodium chloride stresses, the mannose content in exopolysaccharides decreased while the glucose increased in comparison with non-stress condition. The galactose content was highest under stress condition of pH 8 meantime rhamnose content increased sharply when Lactobacillus plantarum VAL6 was stressed at pH 3. The arabinose content in exopolysaccharides was not detected under non-stress condition but it was recorded in great amounts after 3 h of stress at pH 3. In addition, stress of pH 8 triggered the mRNA expression of epsF gene resulting in galactose-rich EPS synthesis. According to our results, the stresses of pH and sodium chloride enhance the production and change the mRNA expression of epsF gene, leading to differences in the monosaccharide composition of exopolysaccharides.
Highlights
To investigate the effect of environmental stresses on the exopolysaccharide biosynthesis, after 24 h of culture at 37 °C with pH 6.8 and without sodium chloride, Lactobacillus plantarum VAL6 was exposed to different stress conditions, including pH and high sodium chloride concentration treatments
The highest yield of EPS reached to 50.44 g/L when L. plantarum VAL6 was exposed to stress of pH 3
The results demonstrated that the stresses of pH 8 and sodium chloride positively affect the EPS producing ability of L. plantarum VAL6
Summary
To investigate the effect of environmental stresses on the exopolysaccharide biosynthesis, after 24 h of culture at 37 °C with pH 6.8 and without sodium chloride, Lactobacillus plantarum VAL6 was exposed to different stress conditions, including pH (pHs of 3 and 8) and high sodium chloride concentration treatments. Stress of pH 8 triggered the mRNA expression of epsF gene resulting in galactose-rich EPS synthesis. The stresses of pH and sodium chloride enhance the production and change the mRNA expression of epsF gene, leading to differences in the monosaccharide composition of exopolysaccharides. The effect of various environmental conditions can trigger the expression of genes involved in the biosynthesis of EPS in LAB. The EPS synthesized by LAB can contain both common and rare sugars, depending highly on environmental conditions[20]. The proportions of individual monosaccharides in EPS differed when L. delbrueckii subsp. bulgaricus CNRZ 1187 and L. delbrueckii subsp. bulgaricus CNRZ 416 were cultured under various pH conditions[22]
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