Mechanism for collective cell alignment in Myxococcus xanthus bacteria

TL;DR

This study investigates how mechanical interactions and slime trail-following contribute to cell alignment and clustering in Myxococcus xanthus bacteria, using agent-based simulations to replicate observed behaviors.

Contribution

It introduces a biophysical agent-based model demonstrating that mechanical interactions and slime trails explain clustering in reversing and non-reversing M. xanthus cells.

Findings

Mechanical interactions can induce alignment and clustering.

Slime trail-following enables clustering in reversing cells.

Model results match experimental observations.

Abstract

Myxococcus xanthus cells self-organize into aligned groups, clusters, at various stages of their lifecycle. Formation of these clusters is crucial for the complex dynamic multi-cellular behavior of these bacteria. However, the mechanism underlying the cell alignment and clustering is not fully understood. Motivated by studies of clustering in self-propelled rods, we hypothesized that M. xanthus cells can align and form clusters through pure mechanical interactions among cells and between cells and substrate. We test this hypothesis using an agent-based simulation framework in which each agent is based on the biophysical model of an individual M. xanthus cell. We show that model agents, under realistic cell flexibility values, can align and form cell clusters but only when periodic reversals of cell directions are suppressed. However, by extending our model to introduce the observed ability of cells to deposit and follow slime trails, we show that effective trail-following leads to clusters in reversing cells. Furthermore, we conclude that mechanical cell alignment combined with slime-trail-following is sufficient to explain the distinct clustering behaviors observed for wild-type and non-reversing M. xanthus mutants in recent experiments. Our results are robust to variation in model parameters, match the experimentally observed trends and can be applied to understand surface motility patterns of other bacterial species.