Nine fungal species were isolated from Egyptian soil. They were identified as Aspergillus niger, Aspergillus fumigatus, Aspergillus terrus, Aspergillus flavus, Trichoderma spp., Fusarium spp., Pencillium spp., Mucor spp. and Alternaria spp. The efficiency of the isolated fungi for phosphate ore (Rock phosphate and Tricalcium phosphate) solublization was studied. A. niger and A. fumigatus showed the highest solublization value. The optimum growth parameters for phosphate ore solublization by both fungi were, 28°C, 10days incubation period, 1% ore concentration, initial pH 6.5-7, sucrose as a carbon source, NaNO3 as a nitrogen source for A. niger and NH4Cl for A. fumigatus. The amount of solublized phosphate from ores (Rock phosphate and Tricalcium phosphate) under optimum conditions reached to approximately 78% and 74% for A. niger, respectively whereas, it was 56% and 54% for A. fumigatus, respectively. Total amount of organic acids produced by both fungi in the growth medium containing rock phosphate was higher than in the control medium. The presence of rock phosphate in the growth medium was highly stimulated the production of oxalic and acetic acid by A. niger. While, it stimulated oxalic and malic acid by A. fumigatus. Whereas, formic and citric acid was high in the control medium of both fungi and only little amounts was detected in rock phosphate containing medium, this may refer to the consumption of both acids in the solublization process.
Key words: Phosphate solublization, Organic acids, Soil fungi