Lecture Notes on Mechanics of Single Cells

Presenter

• Rico (Symbiosis Pasta)
• Working with Professors Casey Huang and Julie Theriot

Research Area

• Focus: Mechanics of Single Cells
• Goal: Understanding how cells exert and control forces necessary for basic functions (growth, division, movement)

Key Concepts

Osmotic Pressure

• Main force used by single cells
• Analogy: Bacterial cell = microscopic water balloon
  • High water pressure inside the cell (osmotic pressure)
  • Caused by high concentration of solutes (DNA, proteins, amino acids, ions)
  • Similar to pressure in a balloon (higher concentration inside than outside)

Challenges and Benefits

• Blessing: Facilitates physical processes
• Curse: High pressure can exceed that in car tires
• Cells use cell wall to withstand this pressure and avoid exploding

Cell Wall

• Polymeric and rubber-like stiffness
• Role: Sustain osmotic pressure and prevent explosion
• Challenge: Growth despite the stiff cell wall

Hypothesis

• Cells use osmotic pressure to stretch the cell wall during growth, like inflating a balloon

Experimental Approach

• Method: Make movies of cells under a microscope
  • Label cell walls with a fluorescent stain
  • Alter osmotic pressure by changing the medium's osmolarity

Observations

E. coli

• Little effect on growth when altering osmotic pressure
• Even without osmotic pressure, growth continues

Soil Bacterium

• Thick cell wall
• Reduced osmotic pressure proportionally decreases growth rate
• Increased osmotic pressure leads to oscillations in growth rate

Conclusion

• Two mechanisms for cell wall expansion in bacteria:
  1. Pressure-independent expansion
  2. Pressure-dependent expansion
• Co-evolution with cell wall's ultrastructure (thickness)

Current Work

• Modeling processes as dynamical systems
• Integrating cell wall mechanics with bacterial osmotic pressure regulation

Contact

• Rico invites questions and further interest via email

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Summary

Rico's research highlights how bacteria utilize osmotic pressure for growth, revealing different mechanisms based on the cell wall's construction. The study exemplifies how pressure impacts bacterial growth differently, suggesting evolutionary adaptation in cell structures.