Download Biophysics Seminar

The Response of Bacterial Growth and Division
to
Osmotic Shock
Rico Rojas
Huang and Theriot Labs
Simbios Center for Biomedical Computation
Stanford Biophysics Seminar
How do bacterial cells grow and divide:
How
do bacterial
cells grow and
divide:
1)
What
are the mechanical
forces
that drive these
1) What
are the mechanical forces that drive these
processes?
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.
Gram negatives: P1 atm (h3nm)
Gram positives: P10 atm (h30nm)
P  (Cin  Cout )T
E. coli, wall stained with WGA
Does cell wall expansion, and therefore cell growth,

depend on osmotic pressure?
Measuring the response of E. coli to oscillatory osmotic shock
P  (Cin  Cout )T

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.,
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!