[Colony structure of a consortium of nitrogen-fixing bacteria]

Colonies produced by a consortium of nitrifying bacteria were studied using light and electron microscopy. The colonies were obtained by direct plating of inoculum from a two-stage nonsterile chemostat fermentor and by repeatedly passing the microbial community of the fermentor through selective media containing ammonium or nitrite. The colonies studied can be characterized by a specific combination of six types of cells differing in their ultrastructure and spatial location within the colony. The types of cells occurring within a given colony were found to depend on the nitrogen compound present in the medium. As a result of our study, morphological features of colonial bacterial communities were preliminarily identified. The proposed approach can be viewed as a method to describe microbial associations and communities.