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

Outline 1.Background and motivation for measuring the growth-rate response to osmotic shock. 2.The case of E. coli. Review of old data: hyperosmotic shocks. New data: Hypoosmotic shocks and MreB motion during osmotic shocks. 3.Brief comparison to the experimental results from B. subtilis. 4.Chalk talk: simple theory comparing the mechanics of Gram-negative and Gram-positive bacteria. 5.Preliminary results from V. cholera and P. aeruginosa. 6.Mini-presentation by Alex Cobb.

B. subtilis Background: osmotic pressure and the cell wall.

History of the idea that osmotic pressure drives cell growth

Christian, 1955 History: Growth rate and medium osmolarity are negatively correlated

History: Theories of pressure driven bacterial growth. Koch, 1980s Jiang, 2010 Furchtgott, 2011Misra, 2013 Amir 2012

Do acute osmotic downshocks reduce elongation rate?

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

Do acute osmotic downshocks reduce elongation rate?

Cell width gives us an indirect measurement of osmotic pressure?

Hyperosmotic shock reduces growth rate at short time scales, but growth is “stored.”

A brief history of “stored growth.” Proseus, 2008

Does MreB velocity depend on osmotic pressure?

Comparing phase tracking to cell wall tracking.

Decreased growth may be due to slight plasmolysis.

Cells do not stretch significantly in response to hypoosmotic shock. 400mM Upshock 400mM Downshock

E. coliV. cholerae V. cholera never stretches upon downshock.

The width reveals that osmotic pressure may be ratcheting down.

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

Consequences of wall thickness for growth strategy. E. coliB. subtilis

Thank you!