FIGURE 1.

Surface motility is induced by extracellular putrescine. Bacterial cultures were diluted in LB medium to an A₆₀₀ of 0.4, and 3 μl of the diluted cultures were dropped onto the center of LBGS plates, supplemented with or without 400 μm putrescine, and incubated at 37 °C. The plates were photographed 40 h after inoculation.