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.