Role of metabolic pathways in Lactobacillus ecology and food quality

• Author / Creator

  Teixeira, Januana S

• Lactobacilli constitute the natural microbiota of cereal fermentations, and their competitiveness has been attributed to the formation of organic acids and various antagonistic compounds. However, these traits alone do not fully explain the prevalence of specific Lactobacillus strains in cereal fermentations. This research demonstrated that the regulation of carbohydrate metabolism and amino acid-based acid resistance contribute to the competitiveness of the obligate heterofermentative Lactobacillus reuteri in cereal substrates.
  The role of α-galactosidase, sucrose phosphorylase, and levansucrase for the conversion of raffinose family oligosaccharides was elucidated. It was shown that levansucrase contributes to the metabolism of raffinose family oligosaccharides, and allows the intermediate accumulation of
  α-galactooligosaccharides as prebiotic compounds. Further studies on the regulation of levansucrase and sucrose phosphorylase demonstrated that these enzymes are induced by sucrose or raffinose, but not repressed by glucose. Regulation is mediated by ScrR; deletion of scrR in L. reuteri resulted in constitutive expression of sucrose phorphorylase and levansucrase. The lack of carbon catabolite repression of sucrose metabolic enzymes in L. reuteri differentiates this organism from other lactobacilli and likely reflects adaptation to plant substrates.
  Analysis of the glutamine / glutamate dependent acid resistance demonstrated that glutamine deamidation increased acid resistance independent of glutamate decarboxylation. Remarkably, glutamate decarboxylation not only increased the intracellular pH. Electrogenic substrate / product antiport also polarized the membrane. Glutamate decarboxylation thus contributed to both components of the transmembrane proton motive force.
  Improved knowledge of the acid resistance of L. reuteri allows a better understanding of L. reuteri to cereal and intestinal ecosystems, and facilitates the selection of strains that can be used as both starter and probiotic cultures.

• Subjects / Keywords

  • Levansucrase
  • Amino acid based acid resistance
  • Sucrose phosphorylase
  • Lactobacillus reuteri
  • Raffinose family oligosaccharides

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3QZ22Q7D

• 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.