New method for isolation of iron and aluminum phosphates solubilizing microogranims using dye

Ravi S. Gadagi and Tongmin Sa

Department of Agricultural Chemistry, Chungbuk National University, Cheongju, Chungbuk, 361-763, KOREA

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The halozone formation on the media containing insoluble phosphates is a basic technique to identify and isolate the phosphate solubilizing microorganisms. Identification and isolation of iron or aluminum phosphate-solubilizing microorganisms on media were found to be difficult, because of halozone formation by phosphate-solubilizing microorganisms was not detected on a media containing iron or aluminum phosphate. An investigation was carried out to develop a method to isolate and identify the phosphate solubilizing microorganisms. Two pH indicator dyes, bromo cresol green (BCG) and bromo phenol blue (BPB) were used to develop a new method for the isolation of microorganisms that solubilize iron and aluminum phosphates based on the fact that the solubilization of iron and aluminum phosphates was associated with the decrease of the pH. Bromo cresol green was found to be superior to bromo phenol blue in terms of clarity and visibility. The use of Reyes’s basal medium plus dye was found to be preferable to that of Pikovaskaya’s medium plus dye in terms of halo zone formation. These results indicated that Reyes’s basal medium plus bromo cresol green is the best medium for the isolation of iron and aluminum phosphates-solubilizing microorganisms. Four efficient iron phosphate solubilizers and five efficient aluminum phosphate solubilizers were isolated on Reyes’s basal medium containing FePO₄ and AlPO₄, respectively, plus bromo cresol green.