Quantifying the flexural rigidity of cyanobacteria using a microfluidic flow cell

Mechanical properties of biofilms and biomats define their structure and contribute to their adaption to a variety of ecological niches. In filamentous cyanobacteria, self-driven multicellular filaments assemble into a complex structure with macroscopic properties such as bundles and vortices. One of the most important parameters relating to the motion of filamentous cyanobacteria is their flexural rigidity or bending modulus, which characterises how flexible the filaments are. We directly measure the flexural rigidity of three species of filamentous cyanobacteria via bending tests in a microfluidic flow device where single cyanobacteria filaments are introduced into flow channel and then deflected by fluid flow. Our measurements are consistent with direct measurements of the Young’s modulus of cell walls made on the same strains using atomic force microscopy and from available data on cell wall thickness of these species. The flexural rigidity of filamentous cyanobacteria will control how individual filaments bend under flow or their own activity allowing us to estimate the free energy and the force exerted on nearby objects. The flexural rigidity alongside filament length and the driving force influence filament motion through crowded environments such as porous media.