Solubilization of aluminum phosphate by specific Penicillium spp.

Abstract

The solubilization of hardly soluble aluminum phosphate (AlPO₄) by specific Penicillium spp. isolated from wheat rhizospheric soils was investigated in Pikovskaya agar and liquid medium, respectively. Most of the Penicillium isolates except P. simplicissimum AP11 and P. variabile AP15 developed clear transparent zone around the colony margin in plate assays. Results of broth assays show that the Penicillium isolates can efficiently solubilize aluminum phosphate in Pikovskaya liquid medium, and vary in their capabilities to release soluble phosphate from aluminum phosphate. All the isolates exhibit different abilities to lower the pH and increase the titratable acidity in the broth compared to the control. HPLC analysis shows that most of the isolates except the species of P. aurantiogriseum can excrete different concentrations of organic acids, including gluconic acid, citric acid, oxalic acid, malic acid and tartaric acids, in the broth. The release of soluble phosphate by the isolate P. oxalicum AP2, which is the best solubilizer of aluminum phosphate among the isolates, is accompanied by a significant drop of pH and an obvious rise of titratable acidity during 7 d of aluminum phosphate-solubilizing experiments. The effects of temperature, initial pH, concentration of aluminum phosphate and shaking speed on aluminum phosphate solubilization by P. oxalicum AP2 were also investigated, and the maximum contents of soluble phosphate released are recorded at temperature 30 °C, initial pH 6, aluminum phosphate concentration 20 g/L, and shaking speed 160 r/min.

Keywords

solubilization / aluminum phosphate / Penicillium spp. / soluble phosphate / Penicillium oxalicum

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