Kinetics of light-switchable surface association of C. reinhardtii populations

Bacterial and microalgal colonization on surfaces produce favorable and adverse effects in technological and medical settings. Consequently, the fundamental aspects of biofilm formation on solid substrates are actively studied. While bacteria have been the main focus of research to understand microbial surface colonization, analogous studies using archetypes in microalgae are thus far elusive. It is known that the flagellar adhesion of the microalga C.reinhardtii is switched on in blue light and switched off under red light [Kreis et al., Nature Physics, 2018]. We exploit the ability to switch the adhesiveness of C. reinhardtii to study the kinetics of adsorption and desorption of cell suspensions on glass using bright field microscopy and image analysis. We observe that both processes exhibit a lag response relative to the time at which blue- or red-light conditions are set and we model this feature using time-delayed Langmuir kinetics. We find that adsorption occurs significantly faster than desorption, with the delay to be an order of magnitude larger. Adsorption experiments of phototactically blind C.reinardtii mutants show that phototaxis does not affect the kinetics of either process. Hence, our method can be used as an assay for characterizing surface colonization.