Bacteria in the Azolla-Anabaena symbiosis

Abstract

The leaf cavities of the fern Azolla contain the N2-fixing cyanobacterium Anabaena azollae and bacteria. These bacteria have been isolated from five Azolla species; they were aerobic, Gram-positive and with a rod-coccus life cycle. Moreover they neither fixed nitrogen nor produced gas, H2S or indole, and they were catalase positive. Nutritionally non-exacting strains grew on mineral salts medium with an ammonium salt and a carbon source. Most of the isolates produced mucilage. The bacteria were identified as Arthrobacter globiformis, A. nicotianae, A. aurescens and A. cristallopoietes or A. pascens. Among the species isolated A. globiformis is the most common. It is likely that the mucilage produced by A. globiformis and A. aurescens fulfils the function of retaining bacteria and Anabaena in the leaf cavities; moreover the bacteria, alone or together with the endophyte, may contribute to the formation of the envelope, which contains bacteria and algal cells. Source: CAB