Chemical and ultrastructural investigations of Mycobacterium bovis BCG: implications for the molecular structure of the mycobacterial cell envelope.
The mycobacterial cell wall visualized by transmission electron microscopy (TEM) of thin sections of resin-embedded specimens is generally believed to consist of an electron-dense peptidoglycan, an electron-transparent arabinogalactanmycolate layer and an electron-dense outer layer (OL). In addition, a pseudocapsule known as the 'electron-transparent zone' (ETZ) has been observed after phagocytosis of mycobacteria by macrophages. TEM of thin sections of Mycobacterium bovis BCG, Tice substrain, revealed an OL bilayer, each of which measured 2-4 nm in diameter. The intermediate electron-transparent layer varied from 1 to about 250 nm in diameter and appears to be a previously observed oxygen-dependent amorphous integument that consists of hot water-extractable neutral polysaccharides, especially a recently characterized alpha glucan, comprising about 12% of the dry cell weight. This and other recent studies of BCG have revealed cell-surface features that may provide a better understanding of the outer mycobacterial cell envelope.
Institute for Tuberculosis Research, College of Pharmacy, University of Illinois at Chicago 60607, USA.
M E
ME
Klegerman
P O
PO
Devadoss
J L
JL
Garrido
H R
HR
Reyes
M J
MJ
Groves
D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D002473:Cell Wall / Q000737:chemistry* / Q000648:ultrastructure*; D005936:Glucans / Q000032:analysis / Q000378:metabolism; D006358:Hot Temperature; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D009163:Mycobacterium bovis / Q000737:chemistry* / Q000648:ultrastructure*; D011135:Polysaccharides, Bacterial / Q000032:analysis / Q000502:physiology
D005936:Glucans; D011135:Polysaccharides, Bacterial