Solubilization of Tricalcium Phosphate and Calcium Phytate by Soil Fungi

Solubilization of bound phosphates by soil microorganismsis one of the vital microbiological processes in soil.Several soil fungi are known to have the property of solubilizing bound phosphates in culture media (1-3).Earlier work in this laboratory has shown that several fungi associated with legume root nodules have the property of solubilizing tricalcium phosphate in culture media (4, 5).In the present study, 48 isolates of fungi from Delhi and Ludhiana soils (6) were screened for their potentialities to solubilize tricalcium phosphate and calcium phytate in culture media.The fungi were grown in 50 ml Richard's synthetic medium (10 g KN03, 2.0 g MgSO4.7H2O,0.001 g FeCl3, 50 g sucrose in 1 litre distilled water) i7 250 ml conical flasks.Each flask containing 50 ml of the medium received 50 mg of tricalcium phosphate or calcium phosphate.The flasks were sterilized at 15lbs pressure for 20 minutes and inoculated with uniform mycelial or spore suspension of fungi in water from 1 week old cultures.Flasks which were not inoculated with fungi served as controls.At the end of 21 days at 28°, the contents of the flasks were filtered through Whatman No. 1 filter paper.The mats were discarded and the following information obtained from the culture filtrates which were made up to a known volume -i) the pH using Beckman's glass electrode pH meter and ii) the amount of phosphorus in excess of that released by mere autoclaving of the medium as found in uninoculated flasks ; the figures indicated the extent to which fungal isolates solubilized insoluble phosphates in the medium.Phosphorus was determined colorimetrically by the vanado molybdate method of KOEING and JOHNSON (7) and expressed in terms of P205 in mg per 50 ml medium.The results are presented in Table 1.Among the 48 isolates of fungi screened for their ability to solubilize tricalcium phosphate, 17 of them were significantly effective in this regard.