Direct observation of bioconvection in Chlamydomonas reinhardtii

Abstract

Bioconvection of motile cells of Chlamydomonas reinhardtii was observed directly by a custom-made horizontal microscope. Upon illumination from above, the cells accumulated at the surface of culture medium, and then distinct paths were formed through which cells were rapidly dropping. The dropping cells were aggregated. This observation suggests that intercellular interaction is important in the bioconvection in this alga. This is in clear contrast with previous studies of fluid dynamics that were based on the assumption that each cell is a linearly moving ellipsoid having negligible intercellular interactions.