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.
Highlights
Myxococcus xanthus is a model organism for studying self-organization behavior in bacteria [1]
We investigate the role of mechanical interactions in the formation of aligned cell groups in Myxococcus xanthus, a model organism of bacterial self-organization
We developed a computational model that simulates mechanical interactions among a large number of model agents
Summary
Myxococcus xanthus is a model organism for studying self-organization behavior in bacteria [1]. These rod-shaped bacteria are known for their ability to collectively move on solid surfaces. This collective movement allows cells to self-organize into a variety of dynamic multi-cellular patterns [2,3]. When cells come into direct contact with other bacteria that can serve as their prey, M. xanthus cells self-organize into ripples, i.e., bands of traveling high-cell-density waves [4,5,6]. If nutrients are limited, cells initiate a multi-cellular development program resulting in their aggregation into 3-dimensional mounds called fruiting bodies [7,8]
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