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Cell Rheology The mechanical properties of the bacterium and how they regulate cell growth. Rico Rojas Huang and Theriot Labs. Goal: To measure and understand how cell growth depends on the osmotic pressure within the cell. Vibrio.

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Presentation Transcript
slide1

Cell Rheology

The mechanical properties of the bacterium and how they regulate cell growth

Rico Rojas

Huang and Theriot Labs

slide3

Goal: To measure and understand how cell growth depends on the osmotic pressure within the cell.

Vibrio

slide4

The osmotic pressure within bacteria is much higher than atmospheric pressure.

Morse Equation

Gram negatives: P ~ 1 atm

Gram positives: P ~ 10 atm

slide5

The bacterial cell wall is a cross-linked polymeric gel that encloses the cell.

Polysaccharides

Polypeptides

Gan et al., 2008

Bacillus

slide6

Mechanical stress the in cell wall balances the turgor pressure and stretches the wall.

ε = strain =Δl/le

Bacillus

Does stress also determine strain rate of the cell wall, i.e., growth rate of the cell?

slide7

Ball-and-Spring Model of the Cell Wall

χ Cross-Link Conc.

ξ Mesh Size

Spring Constant

Rate of Cross-Link Dissociation

Strain Rate

slide9

Biological materials have complex mechanical properties.

ActinRheology

A Rheometer

Koenderink et al., 2006

slide10

Characterizing the response of cells to changes in osmolarity – the “Cell Rheometer.”

slide17

The outer membrane may bear significant stress

PlasmolysisDissolution of outer membrane

Plasmolyzed

Pressurized

Lysed

slide20

Too simple a model

I. Constitutive Equation

{

{

Elasticity

Growth

II. Morse Equation

III. Osmoregulation

slide21

For this year:

  • Finish characterizing the mechanics of the cell wall and osmoregulatory mechanisms.
  • Write cell-scale model that integrates these with growth/wall synthesis.

Jen Hsin