The periseptal annulus: An organel in Gram-negative bacteria

Evidence is presented that the site of cell division in Salmonella typhimurium is flanked by two circumferential zones of cell envelope differentiation, the periseptal annuli, which sep- arate the division site from the remainder of the cell envelope. Each annulus is, composed of a continuous structure in which the mem- branous elements of the cell envelope are closely associated with the murein cytoskeleton. The paired annuli appear early in the di- vision process and the region between them defines a new cellular domain, the periseptal compartment, within which the division septum is formed.