Spherical E. coli due to elevated levels of D-alanine carboxypeptidase.

Abstract

The characteristic shape of bacterial cells is maintained by the strength and form of the murein layer of the cell wall1. Thus, rod-shaped bacteria need to synthesize a rod-shaped murein. The shape of the murein may be determined by the properties of the penicillin-binding proteins (PBPs) that catalyse the insertion of murein precursors into the cell wall2. In Escherichia coli inhibition of PBPs produces characteristic effects on bacterial morphology. For example, inactivation of PBP 2 results in an inability to synthesize cylindrical murein during cell elongation and the growth of E. coli as spherical cells2. We report here that osmotically stable spherical cells of E. coli can also be produced by an increase in the level of PBP 5, a D-alanine carboxypeptidase3, and show that these cells, and those produced by inactivation of PBP 2, have the same abnormality in the structure of the newly inserted murein.