E¡ect of nitrogen source on the solubilization of di¡erent inorganic phosphates by an isolate of Penicillium rugulosum and two UV-induced mutants

The mechanisms of action of mineral phosphate solubilization (MPS) were studied in the wild-type Mps‡ Penicillium rugulosum strain IR94-MF1 and in negative (Mps3) and superpositive (Mps‡‡) mutants derived from it. MPS activities were measured in liquid media using sucrose as C source, four N (arginine, nitrate, nitrate+ammonium and ammonium) and P sources (KH2PO4, hydroxyapatite, FePO4 and AlPO4). Ammonium significantly (P6 0.01) decreased phosphate solubilization, and this activity was 1^66 times higher in the Mps‡‡ mutant than in the wild-type depending on the P and N sources used. The Mps‡ phenotype was strongly associated with the production of gluconic or citric acids. The results also suggest for the MPS3 mutant the involvement of the H‡ pump mechanism in the solubilization of small amounts of phosphates. z 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.