Solubilization of phosphate rocks and minerals by a wild-type strain and two UV-induced mutants of Penicillium rugulosum

Two Venezuelan phosphate rocks (PRs), apatite deposits from Monte-Fresco and Navay areas, and two minerals, Florida apatite and Utah variscite were used to investigate phosphate solubilization by the wild type strain IR-94MF1 of Penicillium rugulosum initially selected for its high mineral phosphate activity (Mps(+)) and two of its mutants Mps(++) and Mps(-). In liquid cultures, the three fungal strains showed better growth on the Navay PR than on Monte Fresco PR. The Utah variscite was the best phosphorus (P) source for the growth of the wild type and the Mps(++) mutant. Solubilization of the various P sources by the wild-type IR-94MF1 and the Mps(++) mutant resulted mostly from the action of organic acids. Citric acid seemed to be more active agent for the solubilization of the Utah variscite while gluconic acid appeared to be responsible for the solubilization of the Florida apatite and the Monte Fresco PR. Both organic acids are likely involved in the solubilization of the Navay PR. The Mps(+) mutant did not produce any organic acid when grown on all the P sources used. (C) 2001 Elsevier Science Ltd. All rights reserved.