R. Platero, F. Battistoni, A. Arias, E. Fabiano
Laboratorio de Ecología Microbiana, Departamento de Bioquímica, Unidad Asociada a la Facultad de Ciencias, Instituto de Investigaciones Biológicas Clemente Estable, Ministerio de Educación y Cultura, Av. Italia 3318, Montevideo 11600, Uruguay
Rhizobia are able to acquire iron from different ferri-siderophores, hemin, hemoglobin and leghemoglobin in iron-depleted conditions. Four Tn5-1063a mutants of Sinorhizobium meliloti 242 defective on iron-acquisition were isolated and characterized. Mutant H38, unable to grow on iron-chelated medium, did not produce detectable amount of siderophores. Furthermore, the tagged locus of H38 was almost identical to an araC like gene found in the rhizobactin regulon of S. meliloti 2011. Mutants H26, H36 and H21 presented impaired growth on iron-chelated medium despite that they were still able to produce siderophores. The interrupted DNA region of H21 mapped in rhtA, a gene that encodes the outer membrane receptor of rhizobactin 2011. Tagged loci of H26 and H36 were found to share significant similarities with ABC (ATP-binding cassette) iron transporter genes of several gram-negative bacteria and with two ORFs present in the sequenced chromosome of S. meliloti SU47 predicted to encode ABC iron transport proteins. Despite the relevant role of iron in the rhizobia-legume symbiosis and the predictable importance of possessing high affinity iron acquisition systems, none of these loci were essential for N2-fixation.
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