Localization of ampicillin-sensitive sites in Escherichia coli by electron microscopy.

Growth of Escherichia coli B/r ATCC 12407 (doubling time, 65 to 70 min) in the presence of 500 mug of ampicillin per ml for 15 to 20 min induces a sphere alongside the cell. The position was determined with respect to the length axis of the cell by electron microscopy. Although spheres may be found anywhere, some prominent sites do occur. In the shortest cells, which have a length of about 1.5 mum, they are found at the presumed new cell pole. In slightly older cells (length, about 1.8 mum), the position of the sphere is not well defined. Later on spheres occur predominantly at the cell center. In dividing cells (average length, 2.5 mum) a sphere may also occur at about one-quarter of the cell length. The position of the spheres bears resemblance to sites where a pulse of 3H-labeled diaminopimelic acid is incorporated into the peptidoglycan, as has been found by others.