Intracellular Fe content influences nodulation competitiveness of Sinorhizobium meliloti strains as inocula of alfalfa

Rhizobia, as well as most soil bacteria, frequently face variable Fe conditions. The effects of Fe limitation or starvation upon rhizobia infectiveness are not fully understood. Our aim was to evaluate the effects of Fe limitation as well as the ability to acquire Fe in rhizobia competitiveness. Sinorhizobium meliloti 242 wild type strain and one of two-iron acquisition mutants (2.1 and 5.6) were co-inoculated at equal ratio onto alfalfa plants. Legumes were grown under gnotobiotic conditions in Fe-supplemented or Fe-chelated defined medium. Our results show that highly efficient Fe acquisition systems are involved in nodule competitiveness when Fe availability is low. Moreover, Fe-scarce inocula were out-competed by Fe-sufficient inocula.