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Transcript of Cell Rheology The mechanical properties of the bacterium and how they regulate cell growth Rico...
![Page 1: Cell Rheology The mechanical properties of the bacterium and how they regulate cell growth Rico Rojas Huang and Theriot Labs.](https://reader036.fdocuments.in/reader036/viewer/2022062423/56649f315503460f94c4bd13/html5/thumbnails/1.jpg)
Cell RheologyThe mechanical properties of the bacterium and how they
regulate cell growth
Rico RojasHuang and Theriot Labs
![Page 2: Cell Rheology The mechanical properties of the bacterium and how they regulate cell growth Rico Rojas Huang and Theriot Labs.](https://reader036.fdocuments.in/reader036/viewer/2022062423/56649f315503460f94c4bd13/html5/thumbnails/2.jpg)
![Page 3: Cell Rheology The mechanical properties of the bacterium and how they regulate cell growth Rico Rojas Huang and Theriot Labs.](https://reader036.fdocuments.in/reader036/viewer/2022062423/56649f315503460f94c4bd13/html5/thumbnails/3.jpg)
Goal: To measure and understand how cell growth depends on the osmotic pressure within the cell.
Vibrio
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The osmotic pressure within bacteria is much higher than atmospheric pressure.
€
P ~ (Cin − Cout )
Morse Equation
Gram negatives: P ~ 1 atmGram positives: P ~ 10 atm
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The bacterial cell wall is a cross-linked polymeric gel that encloses the cell.
Polysaccharides Polypeptides
Gan et al., 2008
Bacillus
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Mechanical stress the in cell wall balances the turgor pressure and stretches the wall.
Does stress also determine strain rate of the cell wall, i.e., growth rate of the cell?
Bacillus
ε = strain =Δl/le
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ξ Mesh Size
χ Cross-Link Conc.
Spring Constant
Rate of Cross-Link Dissociation
Ball-and-Spring Model of the Cell Wall
Strain Rate
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Bacteria have a number of mechanisms for regulating their turgor.
Wood, 2006
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Biological materials have complex mechanical properties.
Koenderink et al., 2006
Actin Rheology
A Rheometer
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Characterizing the response of cells to changes in osmolarity – the “Cell Rheometer.”
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Single cell measurements
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Raw Data: length vs. time
T=30 s
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Strain rate vs. time
n=32
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Turgor pressure modulates growth rate
T=30 s
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The phase is constant across a range of driving frequencies
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“Gram-negative” bacteria (e.g. E. coli) have two membranes
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The outer membrane may bear significant stress
Plasmolysis Dissolution of outer membrane
Pressurized
Plasmolyzed
Lysed
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B. subtilis
Comparative study
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B. subtilis E. coli
Highly non-linear osmoregulation in Gram-positive species
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Too simple a model
€
P = RT(Cin − Cout )
€
˙ C in = −α P − P0( )
€
˙ ε ~dP
dt+ kd P
⎛
⎝ ⎜
⎞
⎠ ⎟I. Constitutive Equation
II. Morse Equation
III. Osmoregulation
{ {
GrowthElasticity
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Jen Hsin
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.
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Thanks!