Structure and functions of exopolysaccharide produced by gut commensal Lactobacillus reuteri 100-23

Abstract

Lactobacillus reuteri strain 100-23 together with a Lactobacillus-free mouse model, provides a system with which the molecular traits underpinning bacterial commensalism in vertebrates can be studied. A polysaccharide was extracted from sucrose-containing liquid cultures of strain 100-23. Chemical analysis showed that this exopolysaccharide was a levan (b-2, 6-linked fructan). Mutation of the fructosyl transferase (ftf) gene resulted in loss of exopolysaccharide production. The ftf mutant was able to colonise the murine gastrointestinal tract in the absence of competition, but colonisation was impaired in competition with the wild type. Biofilm formation by the mutant on the forestomach epithelial surface was not impaired and the matrix between cells was indistinguishable from that of the wild type in electron micrographs. Colonisation of the mouse gut by the wild-type strain led to increased proportions of regulatory T cells (Foxp3 þ ) in the spleen, whereas colonisation by the ftf mutant did not. Survival of the mutant in sucrose-containing medium was markedly reduced relative to the wild type. Comparison of the genomic ftf loci of strain 100-23 with other L. reuteri strains suggested that the ftf gene was acquired by lateral gene transfer early in the evolution of the species and subsequently diversified at accelerated rates. Levan production by L. reuteri 100-23 may represent a function acquired by the bacterial species for life in moderate to high-sucrose extra-gastrointestinal environments that has subsequently been diverted to novel uses, including immunomodulation, that aid in colonisation of the murine gut.

Exopolysaccharides Synthesized by Lactobacillus reuteri Protect against Enterotoxigenic Escherichia coli in Piglets

“…Reuteran formed by L. reuteri in the upper intestine of piglets may thus prevent adhesion of pathogens in the distal intestinal tract, including the jejunum. This protective mechanism provides an identifiable benefit to the host and justifies the promotion of L. reuteri from "gut commensal" (45) to "gut symbiont" (39).…”

“…However, L. reuteri also colonize the upper intestinal tract of swine (36,43). L. reuteri produces exopolysaccharides in vivo to form the polysaccharide matrix of bacterial biofilms on nonsecretory epithelia of the upper intestine (36,44,45). Reuteran formed by L. reuteri in the upper intestine of piglets may thus prevent adhesion of pathogens in the distal intestinal tract, including the jejunum.…”

Dynamics of Gut Microbiota in Autoimmune Lupus

“…Lactobacillus rhamnosus GG, for example, suppresses proinflammatory responses by increasing interleukin-10 and regulatory T (Treg) cells (61,62). Several other members of Lactobacillaceae, including L. acidophilus and L. reuteri, were also found to induce anti-inflammatory Treg cells (63,64). Although colonization of Lactobacillaceae in the guts of both humans and mice has been shown to suppress inflammation (65,66), a direct relationship between intestinal Lactobacillaceae and autoimmune lupus has not been established.…”

Effect of Lineage-Specific Metabolic Traits of Lactobacillus reuteri on Sourdough Microbial Ecology

“…Glutamate-mediated acid resistance may support the survival of probiotic lactobacilli during gastric transit (12,15). In rodents, L. reuteri colonizes the forestomach, where sucrose is available to provide fructose as an electron acceptor (44). The conserved pdu-cbi-cob-hem gene cluster in human-associated L. reuteri strains indicates that glycerol metabolism contributes to the competitiveness of the organism in humans.…”