Collective Motion of Ciliates the Microswimmers

Abstract

Ciliates are swimming microorganisms living in aquatic environments. It has been known that they prefer fields as their habitats near nutrient-rich solid-liquid interfaces such as pond bottom walls and waterweed surfaces. We investigated the interaction dynamics of the behavior of ciliates beside a solid surface without nutrients. The ciliates start sliding on the flat wall of glass substrate after collision. Based on the experimental results on the cilia motions of the surface of the cell, we found that the ciliary thrust force becomes asymmetric due to stop ciliary beating caused by the steric interaction between the wall and the cilium, and the asymmetry of the thrust force results in the cell sliding on the wall. Interestingly, this mechanism brings several behaviors of the ciliate known as habitats, cell accumulation on a solid wall and rheotaxis behavior which is swimming ability toward upstream direction. The accumulated cells form a self-crowded granular system.