Effect of nitrogen source on the solubilization of different 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 (Mps(-)) 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 (P < 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 MPS- mutant the involvement of the H+ pump mechanism in the solubilization of small amounts of phosphates. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.