Regulation of cell-wall morphology and growth encoded by plasmids in Shigella dysenteriae type 1.

Shigella dysenteriae type 1, isolated locally, was found to contain six plasmids and these could be eliminated using SDS. A 70-kb plasmid was necessary to maintain the normal cell-wall morphology. Synthesis of nine major membrane proteins (90 to 40 kDa) was severely impaired in all-plasmid cured strains. Electron microscopy revealed a prominent separation between the outer and inner membranes of the cured strains, indicating that plasmid loss led to defects in the cell envelope. The growth rates of the strains having only the 70-kb plasmid and the plasmidless strain were 3- to 30-fold less than in the wild type strain.