Membrane lipid homeostasis and stress resistance in Escherichia coli and Lactobacillus plantarum

• Author / Creator

  Chen, Yuanyao

• Food processing, preservation and storage impose stresses on food bacteria. The maintenance of membrane lipid homeostasis through modification of phospholipids is a key strategy for bacteria to adapt environmental changes and survival in food. Mechanisms of adaptation are generally comparable between probiotics and pathogens. This thesis research aimed to investigate the effect of the conversion of unsaturated fatty acids to hydroxy fatty acids or cyclopropane fatty acids (CFAs) on stress resistance in Lactobacillus plantarum and Escherichia coli. Firstly, L. plantarum TMW1.460 converts linoleic acids to 10-hydroxy-12-octadecenoic acid (10-HOE) and 13-hydroxy-9-octadecenoic acid (13-HOE) by linoleate 10-hydratase (LahA) and linoleate 13-hydratase (LahB). The role of 10-HOE in ethanol tolerance was studied through the disruption of lahA that encodes linoleate 10-hydratase. The results revealed that 10-HOE did not contribute to the ethanol tolerance, but LahA affected the cell surface hydrophobicity. Moreover, deletion of LahA in L. plantarum facilitated the purification of 13-HOE and the demonstration of its antifungal activity against Penicillium roqueforti and Aspergillus niger. Secondly, both heat and pressure resistant strain E. coli AW1.7 and sensitive strain E. coli MG1655 utilized all of the unsaturated fatty acids (C16:1 and C18:1) in the membrane and most of them were converted to CFAs after entry into the stationary growth phase. Through comparison of survival between wild-type and cfa deficient strains in E. coli AW1.7 and MG1655, this thesis demonstrated that the CFA synthesis in E. coli increased the heat, pressure and acid resistance. Thirdly, the cyclopropanation of membrane fatty acids also protected E. coli AW1.7 and its dried cells against the inactivation conducted by supercritical CO2. The lethality of supercritical CO2 was low on dry cells of E. coli. Treatments with gaseous CO2 were more bactericidal for dry cells than supercritical CO2 at 65°C. Remarkably, E. coli AW1.7 was more susceptible than AW1.7 deficient in cfa when subjected to the gaseous CO2 treatment. This study suggested that CO2-induced membrane fluidization and permeabilization are the major causes of microbial inactivation conducted by high pressure carbon dioxide. This thesis research improved our understanding of the contribution of bacterial membrane lipid homeostasis to stress resistance, which facilitates the optimization of the preparation method to protect probiotics and the design of the intervention method to control pathogens in food production.

• Subjects / Keywords

  • High pressure carbon dioxide
  • Escherichia coli
  • Lactobacillus plantarum
  • Cyclopropane fatty acids
  • Hydroxy fatty acids
  • Stress resistance

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3736MD9H

• 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.