Abstract
Myxococcus xanthus performs coordinated social motility of cell groups through the extension and retraction of type IV pili (TFP) on solid surfaces, which requires both TFP and exopolysaccharides (EPS). By submerging cells in a liquid medium containing 1% methylcellulose, M. xanthus TFP-driven motility was induced in isolated cells and independently of EPS. We measured and analyzed the movements of cells using community tracking algorithms, which combine single-cell resolution with statistics from large sample populations. Cells without significant multi-cellular social interactions have surprisingly complex behaviors: EPS− cells exhibited a pronounced increase in the tendency to stand vertically and moved with qualitatively different characteristics than other cells. A decrease in the EPS secretion of cells correlates with a higher instantaneous velocity, but with lower directional persistence in trajectories. Moreover, EPS− cells do not adhere to the surface as strongly as wild-type and EPS overproducing cells, and display a greater tendency to have large deviations between the direction of movement and the cell axis, with cell velocity showing only minimal dependence on the direction of movement. The emerging picture is that EPS does not simply provide rheological resistance to a single mechanism but rather that the availability of EPS impacts motility pattern.
Highlights
Clear how EPS impacts single-cell motility, or how single-cell motility is modified when more cells are involved
Recent work has shown that the relation between EPS and TFP motility can be complex in P. aeruginosa[12,13,14,15]; it is likely that EPS may influence single-cell motility parameters other than cell speed
Using community tracking algorithms[13,17,18], the motility histories of individual M. xanthus cells can be extracted by translating video microscopy movies into searchable databases of cell behavior, and motility patterns can be identified by tracking every cell in the database
Summary
Clear how EPS impacts single-cell motility, or how single-cell motility is modified when more cells are involved. Recent work has shown that the relation between EPS and TFP motility can be complex in P. aeruginosa[12,13,14,15]; it is likely that EPS may influence single-cell motility parameters other than cell speed. It is not clear whether M. xanthus can combine TFP activity with EPS production to produce different motility outcomes. We leverage recent advances in the tracking of early P. aeruginosa biofilm communities to combine single-cell resolution with large sample populations in the motility analysis of M. xanthus[12]. We quantitatively characterized TFP-mediated single-cell motility of M. xanthus and correlated the differences in motility pattern to EPS production
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