# Chiral gliding: Right-handed navigation of filamentous cyanobacteria

## TL;DR

Filamentous cyanobacteria use a right-handed twisting motion to steer toward wet areas when moving across dry surfaces.

## Contribution

A novel chiral steering mechanism is identified that allows cyanobacteria to navigate based on structural chirality and environmental inhomogeneity.

## Key findings

- Filaments curve right on dry surfaces due to intrinsic chirality and rotation.
- Switching gliding direction allows left turns along slime traces.
- Chiral motility transfers structural asymmetry to macroscopic navigation.

## Abstract

Filamentous cyanobacteria use gliding motility to move along solid surfaces. They can respond to environmental stimuli by reversing the direction of motion. Our study reveals an additional mechanism by which gliding cyanobacteria can steer their movement. We show that the intrinsic chirality of a bacterium, which causes rotation about the filament axis, together with an inhomogeneity in the surrounding conditions, bends the filament such that it glides on a curved path. This chiral steering enables a unique navigation strategy that guides the filaments that encounter dry conditions back toward the favorable aqueous environments. Hence, the gliding motility exhibits a mechanism of chirality transfer from the molecular to the macroscopic scale, akin to the establishment of body asymmetry in higher organisms.

Cyanobacteria are the earliest known organisms that produced oxygen through photosynthesis, leading to the oxygen atmosphere that allowed the evolution of more complex life forms. Many species of cyanobacteria exhibit gliding motility along surfaces to navigate complex environments and adapt to fluctuating conditions. Here, we studied the gliding motility of filamentous cyanobacteria Lyngbya lagerheimii at the transition between different physical environments. We show that on a dry surface, a filament adopts a curved shape that turns right while gliding. When a filament switches the gliding direction, the curvature is initially preserved and a filament can turn left as long as it backtracks along a slime trace. We propose a model of chiral motility that explains the bending based on the right-handed rotation of gliding filaments and a velocity mismatch between the leading and the trailing end of the filament. The mechanism involves a unique way of transferring the structural chirality to the macroscale and also a unique physical navigation mechanism.