Molecular and Physiological Characterization of Plant Growth Promoting Rhizobacteria from Rhizosphere Soil in Al-Qassim, Saudi Arabia

Plant growth-promoting bacteria (PGPB) are associated with many plant species. The most widely studied group of PGPB are plant growth-promoting rhizobacteria (PGPR) colonizing the root surfaces. PGPR have shown promise as biofertilizers. Moreover, phosphorous solubilizing bacteria (PSB) are important for crop plants as they increase phosphorous uptake. The goal of this study was the identification of PGPR isolates by 16S rDNA sequencing, and the evaluation of their ability of phosphorus solubilizing and their physiological traits. Eighteen soil samples were collected from the rhizosphere of alfalfa plants in different areas of Al-Qassim region. The isolates were identified using 16S rDNA gene sequencing. Based on 16S rDNA gene sequencing, these bacterial strains were identified under several genera: Enterobacter, Acinetobacter, Pantoea, Stenotrophomonas, Klebsiella and, Serratia. In a total of eighteen isolates from alfalfa, just 4 isolates (Acinetobacter calcoaceticu, Acinetobacter baumannii, Klebsiella  pneumoniae and Serratia marcescens) have showed high ability in phosphorus solubilizing. All the PGPR isolates were able to grow in NaCl up to 6% and temperatures between 35 and 40°C. QUSA 6, identified as Acinetobacter lwoffii, was found to grow even at 50°C. Therefore, these isolates may have the potential to act as plant-growth-promoting rhizobacteria and can enhance plant growth, particularly under stressed environmental conditions.