Fig. 1

Morphology of a growing bacterial colony. Snapshots of a growing colony, from a few cells (a; t = 125 min, N = 15), through the early stages of growth where the colony elongates (b; t = 171 min, N = 56), followed by later stages of growth in which the colony shape becomes less anisotropic (c; t = 216 min, N = 164), up to the time immediately prior to the colony invading the third dimension (d; t = 261 min, N = 475). Inset: The average ratio of long and short axes of 32 colonies plotted against time. The axes are estimated as the square roots of the larger and smaller eigenvalue of the second moment of area. Error bars are standard errors of the mean