The Response of Bacterial Growth and Division to

Osmotic Shock

Rico RojasHuang and Theriot Labs

Simbios Center for Biomedical ComputationStanford Biophysics Seminar

How do bacterial cells grow and divide:1) What are the mechanical forces that drive

these processes?

How do bacterial cells grow and divide:1) What are the mechanical forces that drive

these processes?

How do bacterial cells grow and divide:1) What are the mechanical forces that drive

these processes?2) How are these forces controlled by

chemistry?

Bacteria cells are enclosed by a cell wall, a cross-linked polymer network.

How do you controllably ‘grow’ and divide a polymer network?

The cell wall bears considerable load due to high internal osmotic pressure.

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P = (Cin −Cout )T

Gram negatives: P1 atm (h3nm)Gram positives: P10 atm (h30nm)

Does cell wall expansion, and therefore cell growth, depend on osmotic pressure?

E. coli, wall stained with WGA

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P = (Cin −Cout )T

Measuring the response of E. coli to oscillatory osmotic shock

Dissecting this data reveals a simple mechanism of wall synthesis.

Model: in E. coli synthesis is rate limiting, but osmotic pressure is required.

Bacillus subtilis exhibits a more drastic response to osmotic shock.

The growth rate of B. subtilis rings in response to downshock.

The existence of ringing predicts that we should be able to drive resonance.

Potential Feedback Mechanisms

Pressure Model: osmotic shock triggers nonlinear feedback in osmoregulation.

Synthesis Model: osmotic shock results in an imbalance of wall precursors.

Ringing depends on the availability of wall precursors.

Staphylococcus aureus division.

Lytic enzymes are distributed around the division plane.

Yamada et al., 1996

S. aureus divides extremely fast.

Thanks to Tim Lee

Measuring the response of S. aureus to oscillatory osmotic shock

Osmotic pressure drives S. aureus division.

Conclusions/Working Models:

E. coli

B. subtilis S.

aureus

Thank You!