RELATIONSHIP OF AZOTOBACTER-CHROOCOCCUM SIDEROPHORES WITH NITROGEN-FIXATION

In iron-limited medium, a siderophore producing soil isolate of Azotob acter chroococcum showed a high level of hydroxamate with relatively l ow level of nitrogen fixation. Inclusion of iron in the medium resulte d in increased nitrogen Fixation with decreased hydroxamate production . Under shake culture conditions, the level of both hydroxamate and ca techol type of siderophores decreased after 2 d of incubation in iron- deficient medium. However, under iron-sufficient conditions, both side rophore production and nitrogen fixation increased with time although the level of siderophore was quite low. A number of soil isolates and mutants of A. chroococcum were tested for nitrogen fixation, hydroxama te and catechol. type of siderophore production. Wide variation was ob served in the siderophore level and nitrogen fixation in the cultures tested. Nitrogen fixation was higher in the iron-sufficient medium tha n in iron-limited one while hydroxamate yield was higher in iron-limit ed medium than in the iron-sufficient one in all the cultures. Inclusi on of ammonium acetate in the medium induced catechol synthesis in mor e than 60 % of the cultures.