Solubilization of insoluble inorganic phosphates by a novel temperature-, pH-, and salt-tolerant yeast, Rhodotorula sp. PS4, isolated from seabuckthorn rhizosphere, growing in cold desert of Ladakh, India

The study was aimed to develop biofertilizer solubilizing inorganic phosphates for region experiencing temperature, pH and salt stressed conditions. A yeast strain PS4, which was temperature-, pH- and salt-tolerant and capable of solubilizing insoluble inorganic phosphate was isolated from rhizosphere of seabuckthorn (Hippophae rhamnoides L.), growing in the Indian Trans-Himalaya. Based on morphological, biochemical, whole cell FAME analysis and molecular characterization, strain PS4 was identified as Rhodotorula sp. The soluble phosphate production under optimal conditions at pH 7 and 30°C was 278.3 mg l^-1. Strain PS4 showed ability to solubilize insoluble phosphate under different stress conditions viz. 5-40°C temperature, 1-5% salt concentration and 3-11 pH range. Soluble phosphate production from Ca₃(PO₄)₂ under combined stress conditions at extreme values of temperature, pH and salt concentration showed 81.6-83.2% reduction as compare to optimal conditions after 5 days incubation. The strain solubilize Ca₃(PO₄)₂ to a great extent than FePO₄ and AlPO₄. The solubilization of insoluble phosphate was associated with drop in pH of the culture media. Inoculation of tomato seedling with the strain increased fruit yield, roots and shoot length. Rhodotorula sp. PS4 with phosphate-solubilizing ability under stress conditions appeared to be attractive for exploring their plant growth-promoting activity towards the development of microbial inoculants in stressed region.