Comparative proteomic analyses for elucidating metabolic changes during EPS production under different fermentation temperatures by Lactobacillus plantarum Q823.

Exopolysaccharide (EPS)-producing bacteria are of growing interest in industrial processes, mainly concerning food. Lactic acid bacteria are widely appreciated for their GRAS (generally recognized as safe) status and their ascertained or putative probiotic features. Detailed investigation on what happens at metabolic level during EPS production is scarce in the literature. The facultative heterofermenter Lactobacillus plantarum Q823 was studied in order to compare growth and EPS production at 30°C and 37°C. A higher growth rate was observed at 37°C, whereas, a significantly higher (tenfold increase) EPS amount was produced at 30°C. To understand the molecular mechanisms leading to the different EPS production in the two conditions, a comparative proteomic experiment was performed. The results of the in-gel proteomics revealed that: i) at 37°C a higher abundance of proteins involved in carbon catabolism and nucleic acid biosynthesis together with a significant amount of stress proteins was observed; ii) at 30°C the production of an atypical manganese-containing non-heme catalase (pseudocatalase) was increased, in agreement with previous data reporting that growth-rates of catalase negative Lactobacillus plantarum strains were greater than that of catalase positive strains. Taken together, all these findings provide further insights about the metabolic pathways stimulated during EPS production, and the mechanism that triggers EPS biosynthesis.