Looping Network Meetings

#63 February 10, 2025

Monday 15:00 (Paris/Warsaw time)

Isabelle Eisenmann (University of Amsterdam)

Light-induced phase separation with finite wavelength selection in photophobic micro-algae

Abstract:
Chlamydomonas reinhardtii is a model micro-algae that is both photosynthetic and phototactic. As such, it uses light not only as an energy source but also as a cue to orient in space. We showed that suspensions of photophobic cells can be unstable to density fluctuations, as a consequence of shading interactions mediated by light absorption. In a circular illumination geometry this mechanism leads to the complete phase separation of the system into transient branching patterns, providing the first experimental evidence of finite wavelength selection in an active phase-separating system without birth and death processes. The finite wavelength selection, that can be captured in a simple drift-diffusion framework, is a consequence of a vision-based interaction length scale set by the illumination geometry and depends on global cell density, light intensity and medium viscosity. On the physiological side we showed that algae inside dense areas underwent significantly less photo-damages than in planktonic conditions, thus demonstrating that phototaxis can efficiently contribute to photoprotection on short timescales through collective behaviors.

Recording