Azide-resistant mutants of Azorhizobium caulinodans with enhanced symbiotic effectiveness

Azide-resistant mutants of Azorhizobium caulinodans strains Sb3, S78, SrR13 and SrS8 were isolated and screened for nitrate reductase activity. Select ed nitrate reductase negative mutants were inoculated on Sesbania bispinosa and S. rostrata under sterile conditions in chillum jars to study their sy mbiotic behavior. Azide-resistant mutants exhibited either similar or highe r symbiotic effectiveness than the parent strain after 30 d of plant growth . Nodule mass, nitrogenase activity and uptake hydrogenase activity of the mutants varied depending on the host as well as on the plant growth stage. In comparison to wild-type parent strains, four azide-resistant mutants, Sb 3Az18, S78Az21, SrR13Az17 and SrS8Az6 showed significant increase in nodula tion and nitrogen fixation as well as shoot dry mass of the inoculated plan ts.