Microalgal Adhesion to Model Substrates
A Quantitative in vivo Study on the Biological Mechanisms and Surface Forces
by Christian Titus Kreis
Date of Examination:2017-11-16
Date of issue:2017-12-14
Advisor:Dr. Oliver Bäumchen
Referee:Dr. Oliver Bäumchen
Referee:Prof. Dr. Stefan Klumpp
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Abstract
English
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.
Keywords: Bioadhesion; Biofilm formation; Chlamydomonas; Microalgae; Biotechnology; Flagellar functionality; Force spectroscopy; Micropipettes; Quantitative single cell adhesion study