Lactobacillus plantarum is found in various environmental habitats, including fermentation products and the mammalian gastrointestinal tract, and specific strains are marketed as probiotics: live microorganisms which when administered in adequate amounts confer a health benefit on the host. Probiotic effects are often species - and/or strain-specific. To investigate strain specificity, specific molecular cell envelope structures have been correlated with to specific probiotic functions to unravel the mechanisms of molecular communication between probiotics and host. This thesis research focused on the interactions of candidate cell envelope effector molecules including lipoteichoic acid (LTA), lipo- and glyco-proteins, and extracellular polysaccharides (EPS), of L. plantarum WCFS1 with mammalian host cells. The potential roles in probiotic functionality of Lactobacillus surface molecules in terms of their biosynthesis pathways and structure variations as well as interaction with host Pattern Recognition Receptors (PRRs) and immunomodulatory properties of these molecules were critically reviewed to obtain an overview of probiotic effector molecule research. Subsequently, candidate probiotic molecules from the cell envelope of L. plantarum WCFS1 were studied for their role in bacterial physiology and their role as ligands in Toll-like receptor (TLR) 2 signaling and immunomodulatory properties. The results of this thesis research illustrate strain-specific and variable impacts of the removal of EPS of individual L. plantarum strains on interactions with host. We found that surface molecules not only play important roles in bacterial physiology, but also in the interaction with the host mucosa through PRRs produced by host cells. We propose that bacterial surface molecules form a unique strain-specific signature that elicits a strain-specific response when interacting with host cells.
Thesis I chiao Lee (click for link)