FIG. 1.
Swarming in air or under PDMS. Cells of E. coli strain HCB1668, inoculated at the center of a 150- by 15-mm swarm agar plate (inside diameter, 14 cm), were grown overnight, covered in part by a half-round sheet of PDMS (0.17 mm thick) (right), returned to the incubator for another 1 h, and then photographed. During the final hour, the radius of the swarm increased from ∼2.5 cm to ∼4.5 cm, in essentially the same way whether the swarm was exposed to air or covered by PDMS. The point of inoculation appears as a cluster of small white spots. The larger circular spots (at 3 and 6 o'clock) are air bubbles. The inoculum was a 2-μl droplet of a saturated culture diluted 10−6-fold.