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.Comment: Added paragraph on high cell density simulations (new Supp. Figure
S6) in Discussion section; Moved cell model and simulation procedure from
Supplementary methods to Methods section in Main Tex
