Experimental and theoretical investigation of mechanical responses of bacteria under hypoosmotic pressure

• Author / Creator

  Darabi, Marjan

• Bacteria represent a type of ubiquitous pathogen that respond to environmental changes such
  as osmotic pressure due to their cellular structure. Both Gram-negative and Gram-positive
  bacteria have distinct structure, including a plasma membrane and cell wall. The primary
  difference between them can be characterized by the absence of an outer membrane and the
  presence of thicker peptidoglycan in Gram-positive bacteria. While both bacterial types may
  exhibit different osmotic responses, the osmotic pressure-dependent mechanical responses
  of Gram-positive bacteria have not been thoroughly investigated, compared with those of
  Gram-negative bacteria. Studying the osmotic pressure-dependent morphological change
  and its mathematical model exert some promising utilities in biomedical applications such
  as designing and optimizing therapeutic strategies for drug delivery. For example, changes in
  cell morphology due to osmotic pressure can affect the uptake and release of drugs. Besides,
  mathematical models can predict how different osmotic conditions influence drug transport
  across cell membranes. As most of the antibiotics avoid peptidoglycan synthesis in bacteria
  which leads to osmotic lysis, studying structural change of bacteria under osmotic condition
  assist antibiotics development.
  In this work, we employed a combination of experimental and theoretical approaches to
  study how Peptidoglycan and inner membrane deform under hypoosmotic pressure. Dynamic
  light scattering (DLS) analysis was used to monitor time-dependent changes in the size of the bacteria, Escherichia coli (E. coli, Gram-negative) and Lactobacillus acidophilus
  (L. acidophilus, Gram-positive), over the course of incubation at different osmotic pressure
  conditions. Upon exposure to 300 mOsm of hypoosmotic gradient, the hydrodynamic radius
  of L. acidophilus cells was observed to increase from 0.81±0.05 μm to 1.79±0.06 μm.
  On the other hand, the radius of E. coli was found to increase from 0.45±0.008 μm to
  0.67±0.01 μm at 0 mOsm. Besides, Transmission Electron Microscopy (TEM) is employed
  to capture morphological changes of bacteria through applying hypoosmotic pressure. The
  experimental results were used to develop a mathematical model. Through this model, the
  mechanical behavior of bacteria cell envelope is predicted by formulating equilibrium equations
  which describe deformations of the membrane attached to the meshed structure of
  peptidoglycan. This results in nonlinear partial differential equations which are solved using
  the custom-built Finite Element (FE) scheme. Finite Element Method, a prominent continuum
  approach, intricately dissects complex problems into a finite set of interconnected
  elements. These elements are considered continuous and deformable entities, facilitating a
  comprehensive analysis of the material’s behavior through the examination of these discrete
  components. We used Finite Element Method to elucidate the correlation between applied pressure
  and bacteria deformation. The numerical solver used for solving the governing equations was
  the Newton-Raphson method, seamlessly integrated into the FENICS platform—a Pythonbased
  open-source software dedicated to solving partial differential equations. Based on our
  model, it is predicted that Gram-positive bacteria experience significant out of plane deformation
  on z direction by increasing lateral pressure from 5 MPa to 125.30 MPa. This
  deformation is depicted by the red regions on the deformation contours of the model, and
  vividly shows that the bacteria is stretched under various pressure conditions. Furthermore,
  the heightened tension experienced by the bacteria in different pressure conditions is presented
  on Material displacement contour. It provides valuable insights into the susceptibility of specific regions within Gram-positive bacteria to rupture under increased pressure conditions.
  Particularly, areas with concentrated stress and heightened strain exhibit vulnerability
  to rupture when exposed to elevated pressures. Notably, the maximum displacement is observed
  in regions of the cell where mobility along the vertical z-axis is prominent. Despite
  the need for further research, it was shown that theoretical predictions were well aligned
  with experimental findings, emphasizing the observed shape change of bacteria matching
  the predicted deformation.

• Subjects / Keywords

  • Bacteria
  • Hypoosmotic pressure
  • Finite element method

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-mn4e-hf88

• License

  This thesis is made available by the University of Alberta Library 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.