Structural similarities between a membrane-like surface layer on the cell wall of some microbial cells and the lamellar layer of vesicles formed by short-chain phosphonic acids in water. A freeze-fracture study

Abstract

A thin layer on the cell wall of some microbial cells, among them such of medical importance (Aspergillus niger, Trichophyton sp.), is characterized by a mosaic-like rodlet pattern in freeze-fracture electron microscopy. A very similar texture could be found in freeze-fractured bilayer vesicles of n-octan phosphonic acid in presence of 50% glycerol. The formation of this structure in phosphonic acid vesicles is connected with the transformation of the bilayer into the solid crystalline state by cooling. The texture could be suppressed by a higher cooling velocity. In absence of glycerol by the normal quick freezing procedure predominantly intermediate stages were fixed. For the interpretation of the structures revealed a model is proposed, where trigonal subunits stick together, because they are hydrophobic on the one side. These subunits are small crystals with a diameter of 4--7 nm. They are in principle also able to construct a bilayer arrangement directly by a "subassembly-selfassembly" mechanism of selforganization. The membrane-like layer on the cell wall of microbial cells may consist of a crystalline bilayer arrangement of similar substances.