Exopolysaccharides secretion of Limosilactobacillus fermentum 2-1 based on AI-2 activity

Abstract:

[Background] The LuxS/autoinducer-2 (AI-2) quorum sensing system regulates bacterial adaptation to environmental changes by secreting signal molecules. Exopolysaccharides (EPS) play a crucial role in protecting cells from external environmental stress and damage. However, the relationship between the LuxS/AI-2 system and EPS production remains unclear. [Objective] To investigate the relationship between AI-2 activity and EPS production in Limosilactobacillus fermentum 2-1 cultured under different conditions. [Methods] The phenol-sulfuric acid method and Vibrio harveyi BB170 bioluminescence assay were employed to determine the EPS yield and AI-2 activity, respectively, of L.fermentum 2-1 cultured under different conditions. [Results] The cell growth of L.fermentum 2-1 was the fastest during the early stages of culture, after which the cell density gradually stabilized. The AI-2 activity peaked at the time point of 7 h and then decreased. The EPS production presented a trend of first rising and then declining, reaching the peak of (204.30±15.98) mg/L at the time point of 16 h, which was significantly higher than that at other time points. Both elevated (44 ℃) and declined (23 ℃, 30 ℃) temperatures inhibited the cell density, AI-2 activity, and EPS production. Acidic conditions favored AI-2 secretion but inhibited cell growth and EPS production. AI-2 activity and EPS production were positively correlated with inoculum size within the range of 1%−3%. Changes of the carbon source altered the cell density, AI-2 activity, and EPS production. Addition of exogenous AI-2 at a final concentration of 100 μmol/L promoted EPS production in L.fermentum 2-1 (P<0.05). [Conclusion] Under certain conditions, there is a positive correlation between AI-2 activity and EPS production in L.fermentum 2-1.

Key words:quorum sensing;signal molecule AI-2;Limosilactobacillus fermentum 2-1;exopolysaccharide