Bacterial morphogenesis: learning how cells make cells.

Bacteria furnish tractable models for complex biological processes, and morphogenesis is now taking its turn. We can already explain in general terms how such elementary forms as rods and cocci are produced, and the shapes of several individual organisms are coming into focus. In most bacteria shape is maintained by the cell wall, specifically the peptidoglycan layer, which has the attributes of a strong stiff fabric. Compliance of that fabric with turgor pressure is an important aspect of morphogenesis. The shape of the wall sacculus is determined by the way it is deposited, which is controlled by a cytoskeleton made up of two molecular families. One, related to the eukaryotic tubulins, is responsible for the construction of the septum and the poles. The other, related to eukaryotic actins, localizes peptidoglycan synthesis in the lateral walls of rod-shaped cells. Just how the cytoskeleton itself is organized remains to be discovered, but it seems likely that, as in eukaryotes, the cytoskeleton is produced by self-organized assembly, guided by the fabric of the cell.