Biodiversity of populations of phosphate solubilizing rhizobia that nodulates chickpea in different Spanish soils

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Within rhizobia, two species nodulating chickpea, Mesorhizobium ciceri and Mesorhizobium mediterraneum, are known as good phosphate solubilizers. For this reason, we have analysed the ability to solubilize phosphate of a wide number of strains isolated from Cicer arietinum growing in several soils in Spain. The aim of this work was to analyse microbial populations nodulating chickpea, that are able to solubilize phosphates, using molecular techniques. In the present work we analyzed 19 strains isolated from effective nodules of C. arietinum growing in three soils from the North of Spain. Nineteen strains showed ability to solubilize phosphate in YED-P medium. These strains were separated into 4 groups according to the results obtained by 879F-RAPD fingerprinting. The 16S rDNA sequencing of a representative strain from each group allowed the identification of strains as belonging to the genus Mesorhizobium. Strains from groups I and II showed a 99.4% and 99.2% similarity with M. mediterraneum UPM-CA142T, respectively. The strains from group III were related to M. tianshanense USDA 3592T at a 99.4% similarity level. Finally, the strain from group IV was related to M. ciceri USDA 3383T with a 99.3% similarity. The LMW RNA profiles confirmed these results. Strains from groups I and II showed an identical LMW RNA profile to that of M. mediterraneum UPM-CA142T; the profile of strains from group III was identical to that of M. tianshanense USDA 3592T and the profile of strains from group IV was identical to that of M. ciceri USDA 3383T. Different 879F-RAPD patterns were obtained for strains of the group I, group II and the M. mediterraneum type strain (UPM-CA142T). The 879-RAPD patterns obtained for group III also differed from the pattern shown by M. tianshanense USDA 3592T. Finally, the patterns between group IV and M. ciceri USDA 3383T were also different. These results suggest that groups I and II may be subspecies of M. mediterraneum, group III a subspecies of M. tianshanense and group IV a subspecies of M. ciceri. Nevertheless, more studies are needed to establish the taxonomic status of strains isolated in this study.