Microbial ecology of food fermentations and intestinal ecosystems

• Author / Creator

  Lin,Xiaoxi

• Microbiota are ubiquitous in nature. Similarities as well as differences are present between microbiota in animals and fermentation systems. The aim of the PhD project was to investigate factors affects microbial ecology in rodent and sourdough models.
  To determine how compromised health of the host by tumor and CPT-11 therapies affects intestinal microbiota in tumor bearing rats, qualitative and quantitative taxonomic analyses were combined to characterize intestinal microbiota during CPT-11-based chemotherapy. Both tumor and CPT-11 chemotherapy increased cecal Clostridium cluster XI and Enterobacteriaceae. The effect of dietary fibre was evaluated in the same model. Cecal butyrate concentrations and feed intake were highly correlated. Moreover, a positive correlation of the host expression of MCT1 with body weight as well as a positive correlation of the abundance of bacterial butyryl-CoA gene with cecal butyrate concentrations were obeserved. These correlations support the interpretation that the influence of dietary fibre on CPT-11 toxicity is partially mediated by an increased cecal production of butyrate.
  Similar to intestinal microbiota, in sourdough, cereal substrates contain various compounds that may have selective effect on sourdough microbiota. The effect of growth rate and acid resistance on microbial competitiveness in sourdoughs was evaluated by assessing competitiveness of glycerol-dehydratase (gupCDE) positive and glutamate-decarboxylase (gadB) positive strains of L. reuteri relative to the corresponding null mutants. Both glycerol and glutamate metabolism determine the competitiveness of L. reuteri in sourdough fermentations. Besides competition over shared energy source, microbes also compete with each other by producing antimicrobial compounds. Reutericyclin is an antibiotic produced by sourdough-originated L. reuteri which is bactericidal against most gram-positive bacteria. A combination comparative genomics, bioinformatics analysis, and the characterization of null-mutants was used to determine the genetic determinants of reutericyclin biosynthesis. A gene cluster unique to reutericyclin producers was identified on a genomic island acquired through lateral gene transfer. It includes genes coding for a nonribosomal peptide synthetase (NRPS), a polyketide synthase (PKS), homologues of phlABC, and putative transport and regulatory proteins. The combination of PhlABC homologues with both a NRPS and PKS is exclusive to the lactic acid bacteria Streptococcus mutans, L. plantarum and L. reuteri, indicating that the genes in these organisms share a common evolutionary origin.

• Subjects / Keywords

  • Ecology
  • Fermentation
  • Microbial
  • Microbiota
  • Sourdough

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3WM38

• 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.