The image shows the colony pattern that emerges during the E. coli bacteria development on a semisolid surface after 1 week of growth.

MG1655 E. coli K-12 strain was cultivated overnight in an Erlenmeyer flask containing 10 ml of Luria Bertani (LB, 1% Difco bacto-tryptone, 0.5 % Difco yeast extract, 0.5 % NaCl) broth at 37ºC until the stationary-phase of growth was reached. A 2.5 µl aliquot of this culture was inoculated on the semisolid surface of a Petri swarming plate: 1% Difco Bacto-tryptone, 0.5 % Difco Yeast extract, 0.5 % NaCl. The liquid medium was harnessed with 1% Difco agar to create a semisolid gel. The plate was incubated in an oven for 72 hours at 30ºC. After this time the plate was mantained a week at room temperature and then was photographed with epilumination using an Olympus CCD device DP70 camera fitted with an optical zoom. The total size of the colony image is 3.5 cm.

For more information see Zorzano et al. (Phys. Rev. E 2005) and Gómez-Gómez et al. (BMC Biol. 2007).