Swimming behavior of Paramecium in crowded environments

Paramecium is a large unicellular ciliate (100-300 µm long) that swims in fresh water environments. Its swimming behavior is classically described as alternations between “straight” paths and abrupt changes in direction, known as the avoiding reaction (AR). This AR can either be spontaneous or induced by mechanosensitive contacts with obstacles. No quantitative measurements of this swimming behavior at both local length scales and large times have been provided so far. Here, we report on extensive measurements of the trajectories of Paramecium tetraurelia in engineered environments with and without obstacles. At large times, we find that Paramecium’s motion is diffusive-like and our preliminary results suggest that the diffusion constant decreases with the obstacles density. We are currently investigating the local details of the mechanosensitive AR in order to understand how this diffusive regime depends on the mechanosensitivity of Paramecium.