Structure, function and biogenesis of the mycobacterial cell wall.

Structure of the mycobacterial cell wall Present-day understanding of the architecture of the mycobacterial cell wall arises from excellent electron-microscopic studies which demonstrate alternating zones of electron density and transparency almost reminiscent of Gram-negative cell walls and clearly pointing to a substantial lipid barrier [l]. This evidence is in accord with the chemical models of the mycobacterial envelope proposed by Minnikin [Z] of a substantial lipid permeability barrier, a staggered pseudoouter membrane contributed in one-half by the meromycolate and a-chains of mycolic acids and in the other half by an assortment of free lipids with medium-chain fatty acids (e.g. the mycocerosates of the phenolic glycolipids) and shortchain fatty acids (e.g. phospholipids). This concept of a staggered pseudo-outer membrane has received credence from the recent permeability, X-ray diffraction, calorimetry and bio-