The Response of Bacterial Growth to Osmotic Shock

The Response of Bacterial Growth to Osmotic Shock Rico Rojas Theriot and Huang Labs Simbios Center for Biomedical Computation

“Do not worry about your difficulties in mathematics. I can assure you mine are still greater. ” –Albert Einstein, in response to a letter from a grade school student who was having trouble with math

Background E. coli h=3 nm P=1 atm (Deng, 2011) B. subtilis h=40 nm P=10 atm (Whatmore, 1990)

E. coli grows faster after upshock than it does at steady state.

B. subtilis grows slower after upshock than it does at steady state.

Consequences of wall thickness E. coli B. subtilis

Layered wall dynamics yield a growth rate dependence on pressure Force balance Deformation/Advectio n

Ringing may be a phenomenon general to Gram-positive species.

Scaling rules will be strong constraints on this model.

Scaling rules will be strong constraints on this model.

Ringing depends on the availability of wall precursors.

Do the cells ring upon upshock? Sort of.

Potential Feedback Mechanisms Pressure Model: osmotic shock triggers nonlinear feedback in osmoregulation. Synthesis Model: osmotic shock results in an imbalance of wall precursors.

The layered model yields a ringing-like response

Including strain-stiffening accentuates ringing somewhat.

Dynamic pressure can explain the undershoot.

Vancomycin vs. Ramoplanin

Vancomycin vs. Ramoplanin

Can we calibrate the PG biosynthetic pathway in time?

To do: -Modularize the model. -Characterize the different qualitative behaviors across parameter space. -Figure out whether ion channels are doing anything or not.

Conclusions/Working Models: B. subtilis: Osmotic shock results in E. coli: Synthesis is rate limiting, but osmotic pressure is required for an imbalance of cell wall precursors. growth.