Solubilization of CAHPO4 and ALPO4 by Aspergillus niger in culture media with different carbon and nitrogen sources

The solubilization of inorganic phosphates by microorganisms supplies phosphates for plant nutrition and increases their growth. The solubilization of CaHPO4 (Ca- P) and AlPO4 (Al- P) by Aspergillus niger using several carbon and nitrogen sources was studied. Solubilization of Ca- P was enhanced when the carbon sources were mannitol, maltose, galactose and glucose (in that order). Galactose, sucrose and maltose were the carbon sources that enhanced the solubilization of Al- P. More extensive growth, acid production, and decrease in pH were obtained in the Al- P medium than in the Ca- P medium, however, the quantity of solubilized phosphate was 12% less. Phosphate solubilization was related to acid production, pH drop and fungal growth in the culture medium. The results of a study carried out under abiotic conditions showed that organic acids solubilize more Ca- P than Al- P. Evaluating the effect of the nitrogen source, the solubilization of Ca- P or Al- P decreased in the following order: glycine > NH4Cl > NaNO3 and NH4NO3 > urea > (NH4) 2SO4, respectively. Ammoniacal nitrogen (NH4 (+)- N) sources were the most effective in the production of acids and in lowering of the pH.