The ultrastructure of microbial colonies was studied. Inside the colonies three types of intercellular contacts were demonstrated. In the colonies of Gram-negative bacteria, the cells were found to be connected by tight adhesions of outer membranes of the cell walls and membrane bridges. In the colonies of Gram-positive bacteria, the intercellular contacts were formed by fusion of peptidoglucan layers of the cell walls. Bacterial cells were differentiated by the presence of a capsule-like envelope. The obtained data indicate the existence of elements of cellular cooperation and specialization in microbial colonies.

The structure of the surface of colonies of various Gram-negative and Gram-positive bacteria was examined by transmission electron microscopy. The results indicate that bacterial colonies in the course of their development produce a film which becomes thicker with increased duration of growth. The basic part of the film is an elementary membrane, which is a stable structure with a large surface area. The inner and outer surfaces of the film membrane are covered by amorphous layers. These layers are thicker in the surface film of Gram-negative bacterial colonies than in those of Gram-positive bacteria. Membrane vesicles from the bacterial colonies take part in the formation of the surface film. The presence of the film on the surface of the colonies of different bacteria suggests that this structure may play an important role.

Electron microscopic examination of the morphology of normal Escherichia coli MC4100 and Shigella flexneri cells and their htpR-defective recombinants has shown the presence in the latter of noncrystalline granules after growth at 37 degrees C. The defect of the htpR gene leads to some changes in ultrastructure of bacterial colonies and the intensification of the processes of development and aging of colonies as integral structures. These phenomena are manifested by early formation of intercellular contacts and thick surface films as well as the enhanced destruction of microorganisms. The recombinant Shigella strain grown at 30 degrees C retained its ability to provoke keratoconjunctivitis.

Escherichia coli colony surfaces were examined using SEM and TEM. The results indicated that bacterial colonies in the course of their development produce surface films which become thicker with increased growth duration. Membrane vesicles contribute to the formation of the surface film. The complex organization of the film suggests that it may perform specific functions.