espanolLas rizobacterias promotoras de crecimiento vegetal son reconocidas y estudiadas por sus efectos beneficos en varios cultivos. Cepas de los generos Azotobacter y Pseudomonas se aislaron de suelo rizosferico de cultivos de arroz (Oryza sativa L.) de 10 fincas en el distrito de riego del rio Zulia, Norte de Santander, Colombia. El aislamiento bacteriano se hizo a partir de granulos de suelo y diluciones seriadas de suelo, sembradas en agar Ashby para Azotobacter y King B para Pseudomonas fluorescentes, respectivamente. Cuarenta y dos aislamientos se conservaron en viales con solucion salina esteril (0.85 % NaCl) en refrigeracion a 4 °C y se ingresaron al Banco de Cepas del Laboratorio de Investigaciones en Biologia Aplicada de la Universidad Francisco de Paula Santander, Cucuta, Colombia. Para seleccionar aislamientos con potencial para el desarrollo de inoculantes microbianos, en todas las cepas se determino su capacidad de solubilizacion de fosfato inorganico, fijacion biologica de nitrogeno, sintesis de acido indoloacetico y sideroforos. Con un conglomerado jerarquico de las medianas de las cuatro actividades se seleccionaron cuatro aislamientos por presentar los valores mas cercanos a los testigos disenados como cepas promisorias en las cuatro actividades segun el dendrograma de similitudes. Estas cuatro cepas se identificaron como Pseudomonas putida (RzA027 y RzA035), Azotobacter chrococcum (RzA040) y Azotobacter tropicalis (RzA042) mediante amplificacion del gen 16S ADNr. EnglishThe plant-growth promoting rhizobacteria are recognized and studied for their beneficial effects on several crops. Strains of the Azotobacter and Pseudomonas genera were isolated from rhizospheric soil where rice crops (Oryza sativa L.) are grown, from 10 farms located in the Zulia River’s irrigation district, Norte de Santander, Colombia. The bacterial isolation was obtained from granular soil and serial soil dilutions, which were planted on Ashby and King B agar, for Azotobacter and fluorescent Pseudomonas, respectively. Forty-two isolates were stored in vials with a sterile saline solution (0.85 % NaCl) in a refrigerator at 4 °C and were deposited in the Bank of Strains of the Applied Biology Research Laboratory of the Universidad Francisco de Paula Santander, Cucuta, Colombia. The capacity to solubilize inorganic phosphate, to fix biological nitrogen, and to synthesize indoleacetic acid and siderophores were determined in all strains, in order to select isolates with potential to develop microbial inoculum. With a hierarchical clustering of the medians of the four activities, four isolations were selected because they presented the closest values to the controls designed as promising strains in the four activities, according to the similarity dendrogram. These four strains were identified as Pseudomonas putida (RzA027 and RzA035), Azotobacter chrococcum (RzA040), and Azotobacter tropicalis (RzA042), by amplification of the 16S rDNA gene.