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Zusammenfassung:
Microalgae are the most important primary producers of biomass on Earth. They inherit enormous
technological potential to harness photosynthesis for the sustainable production of biofuels,
proteins, and food components. In aqueous environments, microalgal surface colonization
and biofouling cause severe implications on anthropogenic structures. Despite the fundamental
interest in understanding microalgal adhesion, the biological mechanisms that trigger microalgal
adhesion to surfaces and the surface forces that govern their adhesion remain unknown. In
this work, the flagella-mediated adhesion to surfaces of soil-dwelling, green microalgae is studied
quantitatively on a single-cell level. Micropipette-based force spectroscopy experiments are
performed to quantify microalgal adhesion to model substrates in various experimental configurations
and environmental conditions. In vivo force measurements show that the adhesion of
microalgae to surfaces can be reversibly switched on and off within seconds by tailoring the
light conditions. The light-switchable adhesion appears to be based on a relocalization of the
adhesion-mediating protein. An active adhesion process, termed auto-adhesion, enables the
alga to establish adhesive contact to surfaces once a small part of one flagellum adhered to the
surface. Experiments with other species of the family Chlamydomonadaceae suggest that the
light-switchable flagellar adhesiveness might be a generic trait of soil-dwelling microalgae. Force
spectroscopy experiments on model substrates with tailored intermolecular interactions with
the Chlamydomonas flagella demonstrate that Chlamydomonas inherits an universal adhesion
mechanisms that allows the algae to adhere to virtually all types of substrates. In conjunction
with light-directed motility, the ability to adhere to any surfaces that provide optimal light
exposure might have evolved as an adaptation of photosynthetic organisms to heterogeneous
light conditions in their natural habitats. The findings of this work will raise the interest of an
interdisciplinary audience, from biologists working on behavior and evolution of microalgae to
biophysicists to bioengineers, and might stimulate further work on the molecular biology and
functionality of eukaryotic flagella.
