Figure 2

Inhibitory effect observed is independent of cell contact. Escherichia coli BW25113 was streaked in a square pattern and spotted on LB containing 0.8% agar. Cells streaked in a square pattern exhibit outward growth but no inward expansion (a, top row). The spot inoculant grows outward, uninhibited (a, bottom row). Images were taken at Day 1 and Day 5 of incubation. The two inoculation methods were combined by incubating the square streak for 0, 24, 48, or 72 h, followed by spotting an inoculant on 5 points at a 0.5 cm increment, beginning from the left of the square streak, going clockwise distance (0.5 cm on the left to 2.0 cm below the square streak) (b). Images were taken at Day 1 and Day 5 of incubation after spotting. Longer preincubation of the square streak results in stronger inhibition of the spotted inoculants, with the stronger effect seen with the center inoculant. Central inoculant spotting location highlighted for clarity (b, circles drawn on 48- and 72-h images).