Electron microscopic observations of intracytoplasmic membrane systems and cell division in Mycobacterium lepraemurium.

The fine structures and the interconnections between the intracytoplasmic membrane systems and cell division of murine leprosy bacilli in liver tissue from mice infected intraperitoneally with Mycobacterium lepraemurium, Hawaiian strain, were studied in ultrathin serial sections at the electron microscopic level. Intracellular membranous organelles (mesosomes) were seen as vesicular, tubular and/or lamellar structures. The formation of mesosomes appeared to be initiated by invagination and/or folding of the cytoplasmic membrane. A few dividing bacilli were observed. The lateral extension and the centripetal growth of the septal wall seemed to result from the original development of cytoplasmic membrane occurring at or near the leading edge of the nascent septum. After the septum formation was completely accomplished, the separation of two new daughter cells is assumed to occur. The mesosome was associated with the newly formed cytoplasmic membrane (septal wall). It was shown that both the cytoplasmic membrane and the mesosome played an important part in septum formation.