[Structures cohérentes dans un bio-fluide]
Collective motion of micro-swimmers leads to the emergence of coherent macroscopic structures. In the case of diluted cultures of micro-organisms, a typical dotted pattern can spontaneously appear within a few minutes, even in the absence of external stimulus, a signature of bioconvection. However, we know little about the resilience of bioconvective plumes facing an environmental alteration. Here, we take advantage of the phototactic behaviour of the green micro-algae Chlamydomonas reinhardtii to perturb bioconvection with an asymmetric lightning. Our experiments demonstrate that plumes first disappear, leaving place for a new anisotropic structure at the illuminated wall. We characterise the dynamics of this rising pattern at various scales and propose a mechanism based on the physical properties of the micro-swimmers.
Le mouvement collectif de micro-nageurs peut générer des structures macroscopiques. Les plumes de bioconvection en sont un exemple : elles apparaissent spontanément dans les cultures diluées de micro-organismes. Cependant, l’impact de signaux extérieurs sur ces structures reste peu exploré. Dans cette étude, nous exploitons le comportement phototactique de micro-algues vertes, Chlamydomonas reinhardtii. Elles nagent préférentiellement vers l’une des parois, éclairée, ce qui introduit une asymétrie dans la dynamique. Nos expériences montrent tout d’abord que les plumes de bioconvection disparaissent. Puis, de nouvelles structures anisotropes émergent le long de la paroi. Nous analysons la dynamique de ces motifs à différentes échelles et proposons un mécanisme basé sur les propriétés physiques des micro-nageurs.
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Mots-clés : Hydrodynamique, instabilités, micro-nageur, matière active
Anaëlle Givaudan 1 ; Francesco Picella 1 ; Hélène de Maleprade 1
CC-BY 4.0
@article{CRPHYS_2026__27_G1_7_0,
author = {Ana\"elle Givaudan and Francesco Picella and H\'el\`ene de Maleprade},
title = {Roll formation in a bio-active fluid},
journal = {Comptes Rendus. Physique},
pages = {7--16},
year = {2026},
publisher = {Acad\'emie des sciences, Paris},
volume = {27},
doi = {10.5802/crphys.268},
language = {en},
}
Anaëlle Givaudan; Francesco Picella; Hélène de Maleprade. Roll formation in a bio-active fluid. Comptes Rendus. Physique, Volume 27 (2026), pp. 7-16. doi: 10.5802/crphys.268
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