Control of the localized bioconvection unit of Euglena suspension by manipulating light environment*

Collective motion of active matters within a confined region, i.e. bird flocking, has attracted  attention not only in biology but also in fluid dynamics, and has therefore been investigated extensively. However, there have been few reports on flocking in bioconvection. The present study is focused on the collective motion of Euglena.

Euglena has the negative phototaxis that the individual moves away from a strong light source. When Euglena suspension is illuminated with strong light from below, a coherent structure called “bioconvection” emerges.

Suematsu et al. (JPSJ 2011) showed that the bioconvection in this setup is localized in a certain region in the container. Shoji et al. (JPSJ 2014) revealed the existence of “bioconvection unit” consisting of two convection cells in annular container where radial motion is restricted. The bioconvection unit exists in spatially uniform environment. The control and characteristics of bioconvection unit will contribute to the understanding of localized structure in dissipative systems.

We conducted experiments to control the bioconvection unit by preparing artificial non-uniform light environments and succeeded in controlling its onset in cylindrical container, a more general container shape. The details will be discussed on presentation.