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

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

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  1. Cell Rheology The mechanical properties of the bacterium and how they regulate cell growth Rico Rojas Huang and Theriot Labs

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

  3. The osmotic pressure within bacteria is much higher than atmospheric pressure. Morse Equation Gram negatives: P ~ 1 atm Gram positives: P ~ 10 atm

  4. The bacterial cell wall is a cross-linked polymeric gel that encloses the cell. Polysaccharides Polypeptides Gan et al., 2008 Bacillus

  5. 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?

  6. Ball-and-Spring Model of the Cell Wall χ Cross-Link Conc. ξ Mesh Size Spring Constant Rate of Cross-Link Dissociation Strain Rate

  7. Bacteria have a number of mechanisms for regulating their turgor. Wood, 2006

  8. Biological materials have complex mechanical properties. ActinRheology A Rheometer Koenderink et al., 2006

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

  10. Single cell measurements

  11. Raw Data: length vs. time T=30 s

  12. Strain rate vs. time n=32

  13. Turgor pressure modulates growth rate T=30 s

  14. The phase is constant across a range of driving frequencies

  15. “Gram-negative” bacteria (e.g. E. coli) have two membranes

  16. The outer membrane may bear significant stress PlasmolysisDissolution of outer membrane Plasmolyzed Pressurized Lysed

  17. Comparative study B. subtilis

  18. Highly non-linear osmoregulation in Gram-positive species B. subtilis E. coli

  19. Too simple a model I. Constitutive Equation { { Elasticity Growth II. Morse Equation III. Osmoregulation

  20. 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

  21. Thanks!

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