Factors contributing to the competitiveness of Lactobacillus reuteri in sourdough and rodent gut

  • Author / Creator
    Su, Shu-Wei
  • Lactobacillus reuteri is a common organism in cereal-based foods and a gut symbiont in humans and animals, yet the molecular mechanisms allowing its persistence in various niches are not well understood. L. reuteri LTH2584 produces reutericyclin and persists in industrial sourdoughs, where acidic conditions during fermentation cause acid stress to organisms. Another strain, L. reuteri 100-23, colonizes the murine forestomach, where this type of lactobacilli contributes to digesta preservation through acid production. L. reuteri LTH2584 and 100-23 were studied to gain an understanding of the phylogenetic relationship between these two isolates, as well as the acid resistance mechanisms and the two-component systems that contribute to the persistence of L. reuteri in sourdough and the murine gut. Analysis of genomic content revealed a close evolutionary relationship between the L. reuteri isolates from sourdough and rodent gut. In addition, a novel double crossover method was developed to generate isogenic deletion mutants for the evaluation of competitiveness, while the acid resistance mechanism was assessed by disruption of glutamate decarboxylase (gadB) in L. reuteri 100-23. Glutamate decarboxylase enhanced the ability of L. reuteri to adapt to both acidic environments (in vitro) and sourdough fermentations (in vivo) by decarboxylation of glutamate to γ-aminobutyric acid. Biofilm formation may depend on the cross-communication of the hk430 and cemAKR operons. Several osmoregulatory genes that may also be associated with cell envelope architecture and cell morphology were also identified.

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  • Degree
    Doctor of Philosophy
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