Download Lab Retreat 2011

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 bacterial cell wall is a cross-linked polymeric gel that
encloses the cell.
S-Layer
Outer membrane
Cell wall
Polysaccharides
Inner membrane
Polypeptides
Caulobacter
Gan et al., 2008
The cell wall defines a cell’s shape.
Stella
Acetabularia
Micrasterias
Phycomyces
Cell wall expansion is equivalent to cell growth.
Cell Wall Expansion = Cell growth
Helicobacter
Cell Shape
Cell Function
Caulobacter
Reproduction
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
Mechanical stress the in cell wall balances the turgor
pressure and stretches the wall.
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
t
Furchtgott et al., 2011
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.
Bacteria have a number of mechanisms for regulating
their turgor.
Wood, 2006
Biological materials have complex mechanical properties.
Actin microrheology
Gile, et al.
Koenderink et al., 2006
Characterizing the response of cells to changes in
osmolarity – the “Cell Rheometer.”
Single cell measurements
Turgor Pressure Modulates Growth Rate.
Things to do this year: construct a model
X-link
dissociation
Ý~ kP ~ k(Cin  Cout )


Growth
Rate
Pressure
Conc. of solutes
CÝin ~ f (Cin ,Cout )  g(P)

Solute
Uptake
Solute
Release
Things to do: test the model
1.
2.
3.
4.
Ion channel knockouts
Deprive cells of compatible solutes
Knockout/over-express/purify endopeptidase
Compare different morphologies, species,
kingdoms
Things to do: apply external mechanical force
Squashed Cells
Optical Trap
Other ideas:
1. Functionalized microcapillary
2. MEMS device
Things to do: address the relationship between synthesis
and mechanics
MreB Motion
Garner et al., 2011
Thanks!