Structural mechanics of filamentous cyanobacteria

TL;DR

This study measures the mechanical properties of filamentous cyanobacteria, revealing how their stiffness and shape are maintained, which informs understanding of their collective behavior and potential bioengineering applications.

Contribution

It provides the first quantitative measurements of bending stiffness, Young's modulus, and cell wall thickness for filamentous cyanobacteria, linking mechanical properties to their natural shapes.

Findings

Cyanobacteria stiffness is well-modeled by a flexible rod with a rigid outer wall.

Measured Young's modulus and cell wall thickness support the rod model.

Internal forces maintain the curved shapes during gliding.

Abstract

Filamentous cyanobacteria, forming long strands of connected cells, are one of the earliest and most successful forms of life on Earth. They exhibit self-organised behaviour, forming large-scale patterns in structures like biomats and stromatolites. The mechanical properties of these rigid structures have contributed to their biological success and are important to applications like algae-based biofuel production. For active polymers like these cyanobacteria, one of the most important mechanical properties is the bending modulus, or flexural rigidity. Here, we quantify the bending stiffness of three species of filamentous cyanobacteria using a microfluidic flow device, where single filaments are deflected by fluid flow. This is complemented by measurements of the Young's modulus of the cell wall, via nanoindentation, and the cell wall thickness. We find that the stiffness of the cyanobacteria is well-captured by a simple model of a flexible rod, with most stress carried by a rigid outer wall. Finally, we connect these results to the curved shapes that these cyanobacteria naturally take while gliding, and quantify the forces generated internally to maintain this shape. The measurements can be used to model interactions between filamentous cyanobacteria, or with their environment, and how their collective behaviour emerges from such interactions.