To stick or not to stick - Chlamydomonas Microalgae Switch their Adhesiveness by Light

Optimization through adaptation to the natural habitat represents a general theme in the evolution of life that can be readily observed for cells, microorganisms and even higher-level animals. For microbial life, the ability to adhere to surfaces is ultimately linked to the formation of dense populations called biofilms, which may help to protect the community of cells against external stimuli. In contrast to marine phytoplankton, many photoactive microalgae live in complex environments, such as liquid-infused soil and moist rocks, where they encounter and colonize a plethora of surfaces. We discovered that the adhesion of green microalgae to surfaces can be reversibly switched on and off by light (C. Kreis et al., Nature Physics, 2017). Using a novel micropipette force spectroscopy technique, we measured in vivo single-cell adhesion forces and show that the microalga's flagella provide light-switchable adhesive contacts with the surface. This light-induced adhesion to surfaces is an active and completely reversible process that occurs on a timescale of seconds. Light-switchable adhesiveness is regulated by a blue-light photoreceptor and mediated by flagella membrane proteins that realise substrate-unspecific adhesive contacts.