Calculating vegetative and swarmer cell division times.

We prepared vegetative cells by diluting an overnight culture 1:200 in fresh medium and grew the cells at 30°C with shaking at 200 rpm to an optical density (OD; λ = 600 nm) of 0.6. We prepared swarmer cells as described previously (10). We monitored the growth of P. mirabilis, V. parahaemolyticus, and E. coli vegetative cells over 120 min at 30°C in the microfluidic flow chamber device described in the next section. We performed a similar experiment with P. mirabilis and V. parahaemolyticus swarmers growing over 65 min at 30°C to determine the amount of time that elapsed before the cells divided. We collected images of cells at 1-min intervals and determined the division time for a maximum of 10 generations (for vegetative cells) and 4 division events (for swarmer cells).