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Host-microbe symbiosis : Evolution of a vertebrate symbiont lactobacillus reuteri
The vertebrate digestive tract is home to a complex community of trillions of microorganisms; together they make important contributions to host health, nutrition, development, behavior, and evolution. While these communities are clearly important for vertebrate biology, very little is known about how these microbes have evolved with their hosts, how they remain associated with their hosts and the selective pressures that shape them. To gain insight into the evolutionary history of a vertebrate symbiont, we characterized the population structure and phylogeny of a global collection of Lactobacillus reuteri (L. reuteri) strains from multiple hosts. Both AFLP and MLSA revealed that L. reuteri has diversified into distinct lineages that reflect host origin but not provenance. The evolutionary patterns detected herein indicate a long-term association of L. reuteri lineages with particular vertebrate species and host-driven diversification. Competition experiments in gnotobiotic mice revealed that rodent strains outcompete non-rodent strains indicating that evolution of L. reuteri was adaptive. Hence, it is possible that physiological and immunological differences of the host represent important selective forces that drove host specialization in L. reuteri. To determine if host-adapted strains have evoke a distinct immune response compared to non-host adapted strains, the immune response gnotobiotic mice mono-associated with L. reuteri strains from different phylogenetic lineages was characterized. Overall, most interactions of L. reuteri with the mouse immune system were strain specific, and effects observed in a given strain cannot be extrapolated to other strains, even those that belong to the same lineage. However, maximal levels of specific IgA response was observed during mono-association with rodent strains, and further examination revealed the presence of intestinal IgA in the biofilm matrix. Moreover, in the presence of a functional adaptive immune system, better biofilm formations and enhanced bacterial fitness were observed. In conclusion, the studies presented here demonstrated host-specificity in L. reuteri and revealed potential adaptations that may be responsible for successful long-term co-evolutionary relationships.
Oh, Phaik Lyn, "Host-microbe symbiosis : Evolution of a vertebrate symbiont lactobacillus reuteri" (2014). ETD collection for University of Nebraska - Lincoln. AAI3617432.