Influence of gastrointestinal stress on autoinducer-2 activity of two Lactobacillus species.

Quorum sensing is a bacterial communication signalling system that regulates the expression of certain target genes with autoinducers in a cell density-dependent manner. The universal luxS-mediated quorum sensing using the autoinducer-2 (AI-2) signal is present in a wide variety of bacteria with only sparse information on probiotic lactobacilli. Effective probiotics should exhibit tolerance and adaptation to stress conditions typical of the GIT. Adhesion to human intestinal epithelial cells and competitive exclusion of pathogens are also considered important. The AI-2 signal system plays an important role in the response of probiotic lactobacilli to the surrounding environment. Intraspecies-related changes in quorum signalling in the GIT were determined by monitoring the AI-2 activity of two strains each of Lactobacillus rhamnosus and L. plantarum under various stress conditions. Modulation of the AI-2 activity of all the strains was induced by stress responses to pH, bile acid, temperature, osmotic pressure and starvation, and was both species- and strain-specific. AI-2 inhibition correlated with a reduction in the stress-related genes of L. rhamnosus. We therefore suggest that AI-2 quorum signalling of probiotic lactobacilli may represent one way of adapting to the host's ecosystem and of interacting within the intestinal environment.