Direct evidence of rolling in gliding bacteria

Determine whether gliding bacteria such as Myxococcus xanthus exhibit transverse rolling motion during surface motility powered by spinning, by obtaining direct experimental evidence of sideways rolling concomitant with their spinning-based gliding.

Background

The paper develops a microscopic model of spinning self-propelled rods (active screws) and derives hydrodynamic equations that predict chiral active nematic stresses when rods roll sideways as they spin. Using experimental data on Myxococcus xanthus colonies, the authors infer the presence of chiral flows around nematic defects and estimate a small but nonzero rolling speed consistent with their model.

However, the authors note that there is no direct experimental observation of rolling in gliding bacteria. They suggest that the observed chiral defect flows might serve as indirect evidence and call for experiments to directly detect rolling or identify alternative mechanisms responsible for chiral flows.