1. DSCG liquid crystal’s viscosity: Insight into the motility of bacteria in an anisotropic liquid environment By Ismaël Duchesne, Simon Rainville and Tigran Galstian In this talk Anisotropic medium: DSCG liquid crystal Isotropic and anisotropic motility of flagellar bacteria (E. coli) Speed and orientation of bacteria in DSCG solution Viscosity of DSCG solution

2. www.ulaval.ca Anisotropic liquid environment:  Physical properties depend on the direction (as birefringence) Flagellar bacteria:  Bacteria that may swims in aqueous medium by rotating theirs flagella Why anisotropic motility:  Many biological tissues and media may be anisotropic (biofilms, enriched chitin soils...)  Difficult task: only few studies 2 DSCG liquid crystal’s viscosity: Insight into the motility of bacteria in an anisotropic liquid environment

3. www.ulaval.ca Anisotropic medium: nematic liquid crystal (LC) 3 Temperature

4. www.ulaval.ca Lyotropic LC: cromolyn sodium salt (DSCG) 4 Yu. A. Nastishin and al., Physical Review E, November 2004.

5. www.ulaval.ca Isotropic motility of bacteria: runs and tumbles 5 source: Wikipedia Random walk

6. www.ulaval.ca Anisotropic motility of flagellar bacteria (E. coli) 6

7. www.ulaval.ca Experiments: montages 7 Chamber and light-guided dark-field microscopy Microscope

8. www.ulaval.ca Results: bacterial motility 8 Purely isotropic phase: as if there were no DSCG Pretransitional phase: sticky effect Anisotropic phase: decrease of speed and runs in the direction of the director SpeedOrientation variation

9. www.ulaval.ca Results: viscosity measurements (from diffusion of 0,2-2µm microspheres) 9 Purely isotropic phase: little viscosity increase Pretransitional phase: exponential viscosity increase Anisotropic phase: anisotropic viscosity ViscosityAxial ratio

10. www.ulaval.ca Can we explain the anisotropic motility with the anisotropic viscosity? 10 IsotropicAnisotropic Beads diffusion Swimming bacteria

11. www.ulaval.ca Conclusion 11 Bacteria behave very differently in anisotropic media Viscosity doesn't explain everything (active motility important) “New” pretransitional phase Viscosity increase (aggregation – threshold) Sticky effect New possibilities for controlling motion of microorganisms

12. www.ulaval.ca Acknowledgements 12 Dr Simon Rainville phD students Guillaume Paradis Ismael Duchesne Dr Tigran Galstian phD students Karen Allahverdyan

13. www.ulaval.ca Viscosity dependency to the beads size 13

14. www.ulaval.ca Propulsive force of bacteria 14