Polyphasic
characterization of phosphate-solubilizing bacteria isolated from rhizospheric
soils of the north-eastern region of Portugal
Angel
Valverde, José M. Igual and Emilio Cervantes.
Instituto de Recursos
Naturales y Agrobiología de Salamanca. IRNA-CSIC. Salamanca. SPAIN.
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Phosphate-solubilizing
microorganisms are often used as plant growth promoters. In the frame of a
project focused on the isolation of endosymbionts and ectorhizospheric bacteria
associated with Phaseolus vulgaris plants growing in a
mountain soil at the north-east of Portugal, we obtained six bacterial strains
with high phosphate-solubilizing capacity, as demonstrated by the formation of
“halos” when plated in YED medium supplemented with tri-calcium phosphate.
These
bacterial strains were characterized by a polyphasic approach using both
phenotypic (API 20 NE, API ZYM) and molecular assays (RAPD, with M 13 primer,
TP-RAPD, 16S rDNA sequencing).
TP-RAPD yielded an identical band patterns in the six strains indicating that they belong to the same bacterial species. The 16S rRNA sequence analysis of a group-representative strain revealed a sequence similarity value of 99.48% with Pseudomonas pavonaceae. Moreover, the RAPD fingerprints of these six strains did not show differences, indicating that they form a highly homogenous group. This high homogeneity could be a consequence of the recurring agronomical practices used in this region from the antiquity that include organic fertilization and monoculture of Phaseolus vulgaris.