Dataset of phototactic response kinetics of Chlamydomonas reinhardtii

The directed movement of microorganisms towards light is called phototaxis-a fundamental process shown by many uni- and multi-cellular photosynthetic microorganisms for their survival and growth. Here, we determine the time-dependent response of a population of model phototactic single-celled algae Chlamydomonas reinhardtii to changing light conditions. When the condition changes from dark to light, we show that the response of a dark-adapted isotropic population depends on not just the light intensity but also on the cell number density. On the other hand, when conditions change from light to dark, the time dependence of the recovery from an aligned state to an isotropic state is independent of cell density and light intensity. We find that such kinetics emerge from the coupling between flagellar dynamics, cell speed, and incident photon flux. We further show that existing minimal non-interacting models, that robustly describe the steady state properties of populations of Chlamydomonas under given light conditions, capture this time-dependent phenomenon only for dilute suspensions.

Methods
All experimental data presented here are obtained by quantitatively analysing microscopy images using MATLAB. Data analysis and numerical calculations are performed in MATLAB and Mathematica.