Interplay between phototaxis and photosynthesis in a model motility

Photosynthetic microorganisms are fundamental to the global ecosystem. They form a large portion of the base of major food webs, including oceanic, and contribute about half of all global oxygen production. These organisms also present possible exciting solutions to many of the most pressing global issues, from the production of fuel alternatives to sustainable agriculture. Light management is essential to the function of such organisms. Specifically, spatio-temporal variations provide information critical to biological regulation and impart energy to fuel intracellular processes. Crucially, these organisms must avoid excess light, as even small deviations can cause serious photooxidative cellular damage and death. Motile organisms deploy two strategies to mitigate intense exposure. Firstly, by using light as information, phototaxis (PT) mechanisms redirect organisms towards/away from light. Secondly, by using light as energy, photosynthesis (PS) systems regulate or dissipate excesses, non-photochemical quenching (NPQ). Observations suggest a fundamental link between PS, PT and NPQ, which has not been studied in quantitative detail. However, the links between these strategies is poorly understood. In this work we aim to bridge this gap, combining experimental measurements of the model microswimmer Chlamydomonas reinhardtii and a modelling approach. This is aimed at linking the intracellular level (SP, NPQ) and the extracellular level (PT) to understand how light is managed by motile photosynthetic microorganisms, and further to enable predictions of the responses at the individual and collective levels.