Isolation and phosphate-solubilizing ability of a fungus, Penicillium sp. from soil of an alum mine.

The use of microorganisms to solubilize elemental phosphorus from insoluble rock phosphate is a promising method to greatly reduce not only environmental pollution but also production costs. Phosphate-solubilizing microorganisms were isolated from soils in China, and a fungus strain (PSM11-5) from a soil sample from an alum mine, with the highest phosphate solubilization potential, was selected and identified as a Penicillium sp. Strain PSM11-5 could grow in buffered medium with pH values between 3.0 and 8.0 and showed phosphate solubilizing activity at pH values from 5.0 to 8.0. It also exhibited a degree of tolerance to the heavy metal ions, Cd(2+), Co(2+), and Cr(6+). PSM11-5 could rapidly solubilize tricalcium phosphate, and a high phosphate-solubilizing efficiency of 98% was achieved in an optimized medium. The strain could solubilize rock phosphate and aluminum phosphate with a solubilizing efficiency of approximately 74.5%, but did not solubilize iron phosphate. Solubilization of phosphate depended on acidification. Analysis of PSM11-5 culture supernatants by capillary electrophoresis showed that tricalcium phosphate was solubilized to PO(4) (3-) and Ca(2+) , and that the organic acid produced by the fungus was mainly gluconic acid at approximately ca. 13 g l(-1). In addition, PSM11-5 produced ca. 830 mg l(-1) of citric acid when it was used to solubilize rock phosphate. These excellent properties of strain PSM11-5 suggest that the fungus has potential for agricultural and industrial utilization.