| dc.description.abstracteng | Cyanobacteria are phototrophic prokaryotes that occur in almost any natural habitat on Earth, from polar to tropical climates, from the Archaean to the present. Roughly 2.5 billion years ago, they have generated the atmospheric oxygen on which animal life is based, still contributing significantly to the global fixation of nitrogen and atmospheric carbon. Some filamentous species exhibit gliding motility on surfaces, which provides the basis for intriguing collective behavior. However, the specific mechanisms and the interplay of gliding motility, pattern formation, and aggregation into dense colonies is not understood in detail. Here, the stimuli-dependent self-organization in colonies of filamentous cyanobacteria is investigated. The projects presented are anchored on different length scales, systematically increasing the population size. First, the propulsion forces of individual filaments are measured with buckling experiments in microfluidic devices, revealing a strong correlation to transverse friction. Then, velocity, growth and pigmentation of multiple filaments are monitored in response to different pH and light intensity, showing a positive correlation between gliding velocity and external pH. Nutrient concentration and illumination intensity additionally influence pigmentation of cyanobacteria and morphology of their colonies. Finally, local alignment with and accumulation at illumination boundaries emerges in ensembles of filaments. The results presented here demonstrate that the self-organization of filamentous cyanobacteria depends on various, albeit simple, external factors and provide a foundation for understanding their collective organization and their immense evolutionary success. | de |