The Dependence of Bacterial Cell Growth on Turgor Pressure

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

7. 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.

9. 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

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

12. B. mycoides

13. 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

14. Christian, 1955

15. Measures, 1975

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

17. Characterizing the response of cells to changes in osmolarity

18. Single cell measurements Dye tracing concentration of mannitol in LB

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

20. Strain rate vs. time n=32

21. Turgor pressure modulates growth rate T=30 s

22. The frequency-dependent waveform response of growth rate elucidates the time scale of osmoregulation

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

24. A simple model I. Constitutive Equation { { Elasticity Growth II. Morse Equation III. Osmoregulation

25. A simple solution I. II. III.

26. Data Model

28. Things to do: test and refine the model ? amplitude ω • Ion channel knockouts • Deprive cells of compatible solutes • Knockout/over-express/purify endopeptidase

29. To do: comparative study B. subtilis

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

31. Things to do: apply external mechanical force Optical Trap – w/Tim Squashed Cells - Kian • Other ideas: • Functionalized microcapillary • MEMS device

32. Thanks!