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 bacterial cell wall is a cross-linked polymeric gel that encloses the cell. S-Layer Outer membrane Cell wall Inner membrane PolysaccharidesPolypeptides Gan et al., 2008 Caulobacter

4. Micrasterias Phycomyces Acetabularia Stella The cell wall defines a cell’s shape.

5. Cell Wall Expansion = Cell growth Cell Shape Cell Function Reproduction Helicobacter Caulobacter Cell wall expansion is equivalent to cell growth.

6. The hydraulic pressure within cells, called the turgor pressure, is much higher than atmospheric pressure. Gram negatives: ΔP ~ 1 atm Gram positives: ΔP ~ 10 atm Huang et al., 2008

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

8. Growth of the cell wall requires two processes: 1)Dissipation of elastic energy, i.e. irreversible deformation 2)Addition of new material to the existing wall In theory, the rate of irreversible deformation (or “growth”) depends on the mechanical stress in the cell wall, and therefore on the turgor pressure. See Gaurav’s and Jen’s talks. Furchtgott et al., 2011 t

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

10. Biological materials have complex mechanical properties. Koenderink et al., 2006 Gile, et al. Actin microrheology

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

12. Single cell measurements

13. Turgor Pressure Modulates Growth Rate.

14. Things to do this year: construct a model Growth Rate X-link dissociation Pressure Conc. of solutes Solute Uptake Solute Release

15. Things to do: test the model 1.Ion channel knockouts 2.Deprive cells of compatible solutes 3.Knockout/over-express/purify endopeptidase 4.Compare different morphologies, species, kingdoms

16. Things to do: apply external mechanical force Other ideas: 1.Functionalized microcapillary 2.MEMS device Optical Trap Squashed Cells

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

18. Thanks!