Fig. 1.

Partition of spot shapes, trajectory patterns of the three different microbial species upon imposition of the potassium gradient. (1a) A representative overview of the original frames. The potassium solution (KCl) diffused passively from the inclusion point indicated by the orange bar on the top of the image. (1b) The mask detector delineated the shapes of the three different morphological spots on the transformed binary frames and partitioned them based on the defined TrackMate parameters. (1c) The shape of spots associated with P. parasitica zoospores (P). (1d) The circular shapes associated with sessile forms of V. microstoma (V) on the top; ellipsoidal shapes associated with free-swimming forms of V. microstoma (V) on the bottom. (1e) The detected spot shapes associated with E. aerogenes cells (E). (1f-g-h) trajectory patterns and mean velocity ranges generated after partition of the 3 groups of spots (1f). The confined trajectory pattern of P. parasitica zoospores (group 1) displayed negative chemotactic behavior in response to the potassium gradient, swimming away from higher concentrations. (1 g) V. microstoma (group 2) exhibited mostly linear or sinusoidal trajectories. Sessile forms, encircled in white in 1a and 1 h, did not display any trajectory. (1 h) Trajectories of E. aerogenes (group 3) in proximity to sessile V. microstoma showed characteristic patterns of vortex flows around the sessile Vorticella. At the bottom of the trajectory images 1f, 1 g, and 1 h is the corresponding mean speed (µm/s) color bar, varying from blue/green (low speed) to yellow/red (high speed). Movies were obtained at 10x magnification and analyzed in the Fiji environment. Scale bars: 100 µm.