SIDEROPHORE-MEDIATED IRON ACQUISITION MUTANTS IN RHIZOBIUM-MELILOTI-242 AND ITS EFFECT ON THE NODULATION KINETIC OF ALFALFA NODULES

The aim of the present work was to characterize the iron acquisition s ystem present in Rhizobium meliloti 242. Tn5-mob induced mutagenesis o f Rm 242 was done using standard methods. Mutants obtained were classe d in three general groups: i) those that produced no detectable or fun ctional siderophore, ii) those that overproduce a functional sideropho re, but were unable to grow on iron-starved conditions and, iii) those that overproduce a functional siderophore in both iron-limiting and i ron-sufficient conditions and were able to grow on iron-starved media. According to the properties of the Tn5-mob induced mutants, this syst em appears to be complex, involving different components. The results obtained in plant assays suggest that the high-affinity iron acquisiti on system expressed by the free-living form is not essential for nitro gen-fixation, although it can affect the early events of nodulation. S iderophore mediated competition is a widespread phenomenon among soil microorganisms. The mutants obtained in this work will be a useful too l to study the role of iron uptake in the competition between rhizobia and other soil microorganisms.