The leaf cavities and the sporocarps of the water fern Azolla contain bacteria belonging to the genus Arthrobacter Conn and Dimmick. The number of these bacteria can be decreased by treating the plants with novobiocin and erythromycin. The latter antibiotic kills the Anabaena, so Anabaena free plants can be obtained. In these plants the bacteria disappear almost completely. The novobiocin does not affect the heterocyst differentiation, but it decreases the N2-fixation activity by affecting the synthesis of the dinitrogenase reduciase.
