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The Dependence of Bacterial Cell Growth on Turgor Pressure

The Dependence of Bacterial Cell Growth on Turgor Pressure. Rico Rojas. Goal: To measure and understand how expansion of the bacterial cell wall depends on mechanical force. Vibrio. The osmotic pressure within bacteria is much higher than atmospheric pressure. . Morse Equation.

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The Dependence of Bacterial Cell Growth on Turgor Pressure

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  1. The Dependence of Bacterial Cell Growth on Turgor Pressure Rico Rojas

  2. Goal: To measure and understand how expansion of the bacterial cell wall depends on mechanical force. 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. This growth in size of the cells appears to be the result of the progressive effect of endosmosis. They distend under the influence of the liquid, and gradually expand like soap bubbles expand under the influence of air which distends them. Cell walls themselves are composed of molecules, and also experience development, particularly the trend of expansion.

  7. Ball-and-Spring Model of the Cell Wall χ Cross-Link Conc. ξ Mesh Size Spring Constant Rate of Cross-Link Dissociation Strain Rate Rojas, et al. 2011

  8. Ball-and-Spring Simulation Platform Jen Hsin Furchtgott et al., 2011

  9. B. mycoides

  10. Growth rate depends on the osmolarity of the medium. Growth rate vs. medium osmolarity of Salmonella in different media Conc. of Sucrose or Salt  Scott, 1953; Christian and Scott 1955

  11. Christian, 1955

  12. Measures, 1975

  13. Turgor Determines Growth Rate in Plants Green 1971

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

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

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

  17. Single cell measurements

  18. B. subtilis

  19. Turgor Pressure Modulates Growth Rate. E. coli φ T=1/ω

  20. Things to do this year: construct a dynamical model I. Constitutive Equation { { Elasticity Growth II. Morse’s Equation III. Osmoregulation

  21. Things to do: test the model Data Model

  22. Things to do: test the model η φ ? ? ω ω • Ion channel knockouts • Deprive cells of compatible solutes • Knockout/over-express/purify endopeptidase • Compare different morphologies, species, kingdoms

  23. Things to do: address the relationship between synthesis and mechanics MreB Motion Garner et al., 2011

  24. Things to do: apply external mechanical force Squashed Cells -Kian Optical Trap • Other ideas: • Functionalized microcapillary • MEMS device

  25. Thanks!

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