The present investigation was aimed at the isolation and characterization of phosphate solubilizing bacteria with enhanced tolerant to environmental stress. The bacterial strain isolated from a metal-contaminated soil collected from abandoned mines was identified as Klebsiella oxytoca according to 16S rRNA analysis. The strain proved the ability to solubilize inorganic phosphate under a wide range of pH (4 to 10), temperature (20 to 40°C) and salt concentrations (0 to 7.5% NaCl). However, the maximum phosphate solubilization (615 µg ml-1) was recorded when the medium contained glucose (2%) and ammonium sulphate (0.1%), respectively as the source of carbon and nitrogen and NaCl (2.5%) with pH adjusted to 7 at 35°C. As revealed by the results of plant growth promoting assays on 1-aminocyclo-propane-1-carboxylic acid (ACC) deaminase activity and production of ammonia, hydrogen cyanide (HCN) and indole acitic acid (IAA), the strain was shown to be good plant growth promoter, which was further confirmed by the enhanced growth of mung bean seedlings inoculated with the strain (31.88 and 45.53% higher shoot and root length compared to un-inoculated control). Based on the results, the strain could be identified as an ideal candidate to be included in developing microbial inoculants suit for stress environments.
Key words: Klebsiella oxytoca, phosphate solubilizing bacteria, stress environments, microbial inoculants.
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