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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.

  • Subjects / Keywords
  • Graduation date
    2011-11
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R3166H
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
    English
  • Institution
    University of Alberta
  • Degree level
    Doctoral
  • Department
    • Department of Agricultural, Food and Nutritional Science
  • Supervisor / co-supervisor and their department(s)
    • Gänzle, Michael (Agricultural, Food and Nutritional Science)
  • Examining committee members and their departments
    • Stuart, David (Biochemistry)
    • Giffard, Philip (Menzies School of Health Research, Australia)
    • Stothard, Paul (Agricultural, Food and Nutritional Science)
    • McMullen, Lynn (Agricultural, Food and Nutritional Science)