Initial divisions of three Escherichia coli K-12 cells leading to microcolony formation on agar-coated slides show the development from a single cell to a characteristic four-cell array.

　　Following the first division, cell elongation became asymmetric, so that the two daughter cells elongated preferentially towards each other, displacing their inside poles and continuing to elongate alongside each other until the four poles were aligned. Septation and division occurred during the elongation process so that a characteristic four-celled structure resulted after somewhat less than 2 h of incubation.

　　Selected video frames were photographed off the monitor and are arranged in sequential order from top to bottom to show the development. The numerals at the left of each panel give the time of the video frame (hours:minutes:seconds). (The exact magnifications of these figures were not determined, but they are on the order of x2,000).

James Shapiro and Clara Hsu, Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Ill., USA