A simple model and strategies for orientation in phototactic microorganisms

A simple mathematical model for the signal received by the photoreceptors of microorganisms such as Chlamydomonas and Euglena is described and used to test hypotheses for the control strategies employed by the microorganisms during phototaxis. When a suspension of Euglena gracilis is irradiated by two perpendicular and unpolarized beams of light, the distribution of swimming directions is bidisperse. An alternative to the Jennings-Mast shading hypothesis is proposed and shown to be consistent with this behaviour