RESUMO
Aspergillus sp PS 104, a soil isolate had excellent potential to solubilize rock phosphate in vitro. The process was influenced by the presence of various concentrations of local loess (red soil). The simultaneous occurrence, in our experiment, of high levels of solubilized phosphate and synthesized citric acid, together with the lowest reached pH values, confirmed the role of citric acid in the phosphate solubilization mechanism. When the soil was present, phosphate release was better correlated than citrate synthesis with H+ concentration. Changes in soluble phosphate concentration did not follow a sigmoid pattern. The ability of organism to release phosphatase was also studied. An interesting relationship was observed between the two processes of phosphate mobilization: citric acid synthesis and phosphatase production.