Solubilization of phosphate by a strain of Rhizobium leguminosarum bv. trifolii isolated from Phaseolus vulgaris in El Chaco Arido soil (Argentina)

José Luis Zurdo-Piñeiro¹, Adriana Abril², Alvaro Peix³, Raúl Rivas¹, Pedro F. Mateos¹, Eustoquio Martínez-Molina¹, Encarna Velázquez¹

¹Departamento de Microbiología y Genética, Facultad de Farmacia, Universidad de Salamanca. SPAIN.

²Cátedra de Microbiología Agrícola. Facultad de Agronomía. Universidad de Córdoba. ARGENTINA.

³Instituto de Recursos Naturales y Agrobiología (IRNA). CSIC. Salamanca. SPAIN.

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Several strains were isolated from Phaseolus vulgaris plants growing in a soil from El Chaco Arido (Argentina). Although strains nodulating Phaseolus are not P-solubilizers in plates containing bicalcium phosphate, we tested the isolates and among them, one strain (ARPV02) was able to solubilize phosphate in plates. This strain showed a high ability to nodulate and to fix nitrogen in common bean. Sequencing of 16S rRNA was performed in the strain ARPV02, showing a 100% similarity with the former type strain of Rhizobium trifolii ATCC14480^T. This strain is currently considered as a biovar of species Rhizobium leguminosarum together biovars viceae and phaseoli. These biovars have been defined basing on its ability to nodulate a concrete group of legumes. In this way, strains nodulating Vicia are named Rhizobium leguminosarum bv viciae, strains nodulating Trifolium are considered as belonging to biovar trifolii and those nodulating Phaseolus are included in biovar phaseoli. However, in previous studies we have shown that in some soils strains nodulating Phaseolus belong to biovar trifolii according to their chromosomal background. Therefore the results of the present work are in agreement with our previous results, but in this case the strain was isolated in an American soil whereas in the previous studies the strains belonging to R. leguminosarum bv. trifolii were isolated from Spanish soils. Nevertheless, the phosphate solubilization of the strain ARPV02 coincides with the results obtained in some strains from biovar trifolii endophytic in rice that are able to solubilize phosphates in vitro.