Abstract

Chlamydomonas reinhardtii is an model organism for biflagellate motility studies. They are able to reorient in respond to gravity and achieve upward swimming in quiescent fluid. The dynamics is conventionally quantified by a time scale called B. The swimming direction of algae is stochastic, quantified by rotational diffusivity Dr. Along with the swimming speed vs, the motility parameters of Chlamy have been measured in a number of studies, but less is known about their variation through the cell cycle under synchronised culturing conditions. Besides the known resorption of flagella prior to cell division, which arrests motility, this study has uncovered specific temporal variations of the three swimming parameters through the cell cycle, which are found to associate with the regulation of cell energetics. As a result, the observed collective motion of an algal suspension in response to a down-welling Poiseuille flow varies if cells were prepared from different cell-cycle stages. For the first time, the collective motion are investigated by theoretical predictions parametrised with the cell-cycle dependent motility parameters. The results reinforced the importance of including cell synchronisation and fixed time-point sampling in the experimental protocols of algal motility studies.