Isolation and Characterization of Phosphate-solubilizing Bacteria (PSB) from Bhitarkanika Mangrove Sediments

Abstract

The phosphate solubilizing activity of twenty bacterial isolates obtained on Pikovskaya’s medium from sediments of Bhitarkanika mangrove forest, India were studied. Out of the 20 isolates obtained, 16 were selected on the basis of halo zone on the above medium. These 16 isolates were identified using PIBW in software after Gram’s staining, biochemical characterization, enzymatic assay, sugar utilization and antibiotic sensitivity tests. From the phosphate solubilization index, the most efficient phosphate solubilizers selected were S7, S12, S13, S20 and identified as Bacillus psychrophilus, Bacillus licheniformis, Pseudomonas aeruginosa and Pseudomonas cepacia respectively, producing largest halos of approximately 19 - 23 mm within 8 days of incubation. Spectrophotometric quantification of phosphate solubilization showed that all bacterial species solubilized insoluble phosphate well in a liquid medium which was accompanied by a significant drop in pH from an initial pH 7.0 to 4.3- 5.0 of the medium after 72 hrs. The HPTLC analysis of cell-free spent culture medium from the four bacteria demonstrated that lactic acid was produced by all the bacterial isolates indicating production of organic acids by these mangrove microorganisms as a possible mechanism involved in the solubilization of insoluble calcium phosphate.