Stress Tolerance and Genetic Variability of Phosphate-solubilizing Fluorescent Pseudomonas from the Cold Deserts of the Trans-Himalayas
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Nineteen efficient phosphate-solubilizing fluorescent Pseudomonas from the cold deserts of the trans-Himalayas were screened for stress tolerance against temperature, alkalinity, salinity, calcium salts, and desiccation. Phylogenetic analysis based on 16S rRNA gene sequencing placed these bacteria under three groups with fourteen strains in Group I including Pseudomonas trivialis and P. poae, two strains in Group II together with Pseudomonas kilonensis and P. corrugata, and three strains in Group III along with Pseudomonas jessenii and P. moraviensis. Genetic diversity assessed by ERIC and BOX-PCR revealed variability among strains belonging to the same phylogenetic groups. Cluster analysis based on the growth characteristics under regimes of different stress levels placed the strains into three distinct clusters displaying no correlation to their phylogenetic groups. Stress-tolerant strains differed in the level of decline in phosphate solubilization under increasing intensity of various stress parameters. The highest decrease occurred with 5% CaCO3, followed by 2.5% CaCO3, pH 11, 5% NaCl, temperature of 37°C, 40% PEG, 5% CaSO4, 2.5% NaCl, 2.5% CaSO4, pH 9 and temperature of 15°C. Two strains belonging to Phylogenetic Group I exhibited higher phosphate solubilization at lower temperature. The results revealed that stress-tolerance ability was not limited to any particular phylogenetic group. Knowledge about the genetic variants of phosphate-solubilizing fluorescent Pseudomonas with potential for tolerance to desiccation, alkalinity, temperature, and salinity could be useful in understanding their ecological role under stressful environments of low phosphate availability.
The authors acknowledge the Director, Institute of Himalayan Bioresource Technology for providing the necessary facilities. Thanks are also due to Mr. Digvijaya Singh Naruka for the technical support in operating the DNA Sequencer. The financial support by the Council of Scientific and Industrial Research under the CSIR Network Project “Exploitation of India’s Rich Microbial Diversity” is also acknowledged.
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