Squared algae: stability and propulsion

Microscopic green algae show great diversity in structural complexity, and successfully evolved efficient swimming strategies at low Reynolds numbers. Gonium is one of the simplest multicellular algae, with only 16 cells arranged in a flat squared plate. This peculiar structure is characteristic to these colonies, and I will investigate its mechanical stability. This unique cellular arrangement is also a conundrum for efficient propulsion. Indeed, the swimming of unicellular organisms, like Chlamydomonas, is nowadays widely studied, but it is less clear how a colony made of independent Chlamydomonas-like cells performs coordinated motion. Gonium is therefore a key organism to model the evolution from single-celled to multicellular locomotion. In a second time, I will present experiments investigating the phototactic swimming of Gonium, using trajectory tracking and micro-pipette techniques. I will explain our model linking the individual flagella response to the colony trajectory. This eventually emphasises the importance of biological noise for efficient swimming.