  Filamentous cyanobacteria are one of the oldest and today still most abundant
lifeforms on earth, with manifold implications in ecology and economics. Their
flexible filaments, often several hundred cells long, exhibit gliding motility
in contact with solid surfaces. The underlying force generating mechanism is
not yet understood. Here, we demonstrate that propulsion forces and friction
coefficients are strongly coupled in the gliding motility of filamentous
cyanobacteria. We directly measure their bending moduli using micropipette
force sensors, and quantify propulsion and friction forces by analyzing their
self-buckling behavior, complemented with analytical theory and simulations.
The results indicate that slime extrusion unlikely generates the gliding
forces, but support adhesion-based hypotheses, similar to the better-studied
single-celled myxobacteria. The critical self-buckling lengths align well with
the peaks of natural length distributions, indicating the importance of
self-buckling for the organization of their collective in natural and
artificial settings.
