Ultrastructure of the cell wall and the mechanism of cellular division of a Gram-variable coccus

An ultrastructural study of a Gram-variable coccus was carried out. The cell wall of this microorganism was composed of an inner peptidoglycan layer, a middle electron-transparent compartment, and an undulating trilayered outer membrane. This microorganism also possessed numerous mesosomes which were simple bulb-like invaginations of the cytoplasmic membrane. The mechanism of cellular division involved the formation of a septum by the cytoplasmic membrane and the inner layer of the cell wall. Membranous structures were associated with the developing septum throughout the process. The outer membrane of the cell wall did not invaginate with the inner layer but reformed as the completed septum began to split. In isolated cell wall preparations, no 2-keto-3-deoxyoctonate or heptose could be detected. It is suggested that the Gram-variable cocci previously classified as micrococci may represent a group that is intermediate between true Gram-negative and Gram-positive bacteria.