Collective effects in bacterial suspensions
Résumé
Bacteria are simple living beings endowed, for some of them, with long flagellar filaments that are considered as motility organs. Provided they find a micro- scopic energy source, they use flagella rotation to self-propel in the medium at low Reynolds number. Although planktonic bacteria exhibit a “run and tumble” motility yielding to a large-scale diffusion, dense suspensions of swim- ming bacteria display remarkable properties such as the appearance of collective motions, i.e. local bacterial ordering associated with a characteristic correla- tion length scale, reminiscent of turbulent phenomenon. This behavior emerging from the group confers unconventional macroscopic properties to the suspension and leads to a new paradigmatic approach of these out-of-equilibrium physical and hydrodynamical active systems.