PHYSIOLOGICAL-CHARACTERISTICS OF RHIZOBIUM-MELILOTI 1021-TN5 MUTANTS WITH ALTERED RHIZOBACTIN ACTIVITIES

Rhizobium meliloti 1021 and several Tn5 generated mutants were examined for physiological activities which would reflect the capacity of these strains for efficient iron metabolism. Rhizobactin production in liquid culture, as measured by CAS reactivity, was greatest in R. meliloti 1021 with lesser amounts formed by strains PRR 63 and PRR 62. Examination of the various strains of R meliloti grown under different levels of iron revealed that all strains tested were constitutive for ferric reductase. Evaluation of Medicago saliva L. cultivated in peat pots and inoculated with R meliloti revealed that greatest levels of growth was with R meliloti 1021, the only strain in this study with an efficient rhizobactin system. Evaluation of dinitrogen fixed by nodulated plants grown in a hydroponic system indicated that the amount of nitrogen fixed per bacteroid in the nodule was not constant but was correlated with the rhizobactin producing capability of the R. meliloti strains. Levels of dinitrogen fixed per unit of viable bacteroids was greater with R. meliloti 1021 than with PRR 29 or PRR