Myxococcus xanthus Gliding Motors Are Elastically Coupled to the Substrate as Predicted by the Focal Adhesion Model of Gliding Motility

Abstract

Myxococcus xanthus is a model organism for studying bacterial social behaviors due to its ability to form complex multi-cellular structures. Knowledge of M. xanthus surface gliding motility and the mechanisms that coordinated it are critically important to our understanding of collective cell behaviors. Although the mechanism of gliding motility is still under investigation, recent experiments suggest that there are two possible mechanisms underlying force production for cell motility: the focal adhesion mechanism and the helical rotor mechanism, which differ in the biophysics of the cell–substrate interactions. Whereas the focal adhesion model predicts an elastic coupling, the helical rotor model predicts a viscous coupling. Using a combination of computational modeling, imaging, and force microscopy, we find evidence for elastic coupling in support of the focal adhesion model. Using a biophysical model of the M. xanthus cell, we investigated how the mechanical interactions between cells are affected by interactions with the substrate. Comparison of modeling results with experimental data for cell-cell collision events pointed to a strong, elastic attachment between the cell and substrate. These results are robust to variations in the mechanical and geometrical parameters of the model. We then directly measured the motor-substrate coupling by monitoring the motion of optically trapped beads and find that motor velocity decreases exponentially with opposing load. At high loads, motor velocity approaches zero velocity asymptotically and motors remain bound to beads indicating a strong, elastic attachment.

The Screw-Like Movement of a Gliding Bacterium Is Powered by Spiral Motion of Cell-Surface Adhesins

“…Yet, genetic evidence suggests that there are clear differences in their modes of gliding. Two models have been proposed to explain the gliding of M. xanthus: the focal adhesion model (23,24) and the helical rotor model (6). In the focal adhesion model, multiprotein complexes extend from the cytoplasm to the outer membrane of a cell and attach to an external surface via focal adhesions.…”

Novel mechanisms power bacterial gliding motility

“…First, adhesive materials such as slime are required to allow the helical waves to transmit the propulsive force to the substrate . Second, according to computational modelling, a certain degree of surface adhesion is required for the maintenance of gliding direction (Balagam et al, 2014).…”

A Hybrid Approach for Segmentation and Tracking of Myxococcus Xanthus Swarms

“…Time-lapse confocal microscopy is widely used to visualize the development of M. xanthus swarms over time. Experiments have been conducted to investigate the mechanism of M. xanthus swarming at different scales, from the individual cell’s surface gliding motility [6] to the highly coordinated motions in large swarms [7]. M. xanthus has been recognized as a model organism for studying the collective cell motion principles, which may be generalized to other cellular systems [8].…”