Abstract
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.
Highlights
Phosphorous (P) is one of the most important macronutrients required by plants
Isolation and identification of phosphate solubilizing bacterial strain Selected bacterial strain had a marked solubilizing ability of insoluble phosphate as visualized by the clear zone developed around the colony after 3 days of incubation
Indole acetic acid (IAA) production was determined using the method described by Gutierrez et al (2009)
Summary
Phosphorous (P) is one of the most important macronutrients required by plants. Though soils generally contain high amount of P (0.05%), only very small amount (0.1%) of the total P is available for plant uptake (Chang and Yang, 2009), it is considered to be the most limiting nutrient. M1 (PVK; Pikovskaya, 1948) Composition. 10 g glucose, 0.5 g (NH4)2SO4, 0.1 g MgSO4.7H2O, 0.5 g yeast extract, 0.2 g KCl, 0.2 g NaCl, 0.002 g FeSO4.7H2O, 0.002 g MnSO4.H2O, 5 g. 20 g glucose, 1 g (NH4)2SO4, 0.5 g MgSO4.7H2O, 0.2 g yeast extract, trace FeCl3, trace MnSO4.H2O, 5 g Ca3(PO4) (pH- 6.8).
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