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

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

Inner membrane Polysaccharides Polypeptides

Gan et al., 2008

Caulobacter

Micrasterias

PhycomycesAcetabularia

Stella

The cell wall defines a cell’s shape.

Cell Wall Expansion = Cell growth

Cell Shape

Cell Function

ReproductionHelicobacter

Caulobacter

Cell wall expansion is equivalent to cell growth.

The hydraulic pressure within cells, called the turgor pressure, is much higher than atmospheric pressure.

Gram negatives: ΔP ~ 1 atmGram 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 deformation2) 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., 2011t

Bacteria have a number of mechanisms for regulating their turgor.

Wood, 2006

Biological materials have complex mechanical properties.

Koenderink et al., 2006

Gile, et al.

Actin microrheology

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

€

˙ ε ~ kP ~ k(Cin − Cout )

€

˙ C in ~ f (Cin ,Cout ) − g(P)

Growth Rate

X-linkdissociation

Pressure Conc. of solutes

Solute Uptake

Solute Release

Things to do: test the model

1. Ion channel knockouts2. Deprive cells of compatible solutes3. Knockout/over-express/purify endopeptidase4. Compare different morphologies, species,

kingdoms

Things to do: apply external mechanical force

Other ideas:1. Functionalized microcapillary2. MEMS device

Optical Trap

Squashed Cells

Things to do: address the relationship between synthesis and mechanics

Garner et al., 2011

MreB Motion

Thanks!