Freeze-fracture observations of the cell walls and peribacillary substances of various mycobacteria.

Ultrastructure of the cell wall and peribacillary substances of various mycobacteria (32 strains of 18 species) grown in vitro was studied by a freeze-fracture technique. Peribacillary substances differed in shape among species and even among strains of the same species, and were classified into five types: (1) amorphous substances; (2) multi-layered sheaths with no filamentous units; (3) structures composed of filaments of 2-4 nm diameter, which were further classified into three subtypes according to the arrangement of the filaments; (4) helical fibres; and (5) single fibres, or networks of fibrous structures, with no visible substructures. No strains revealed peribacillary structures resembling those of uncultivable Mycobacterium leprae. These results have implications for the mechanism of freeze-fracturing in mycobacterial walls.