Ultrastructural explanation for snapping postfission movements in Arthrobacter crystallopoietes.

The ultrastructure of dividing rod-stage cells of Arthrobacter crystallopoietes was examined by electron microscopy. The cell walls consist of two layers. During cell division, the inner layer invaginates to form the septum. The outer layer does not participate in septum formation. After septum formation is completed, the two daughter cells remain attached by the outer layer of the cell wall. It appears that localized rupture of the outer layer during further wall growth is responsible for the phenomenon known as "snapping division" or "snapping postfission movement."