Rock Phosphate Solubilization using Oxalic Acid - secreting Laccaria fraterna

摘要

Laccaria fraterna is an ectomycorrhizal fungus commonly associated with conifers and angiosperms. To check whether L. fraterna possess mechanism to solubilize rock phosphate by secreting organic acids, it was grown in Pikovskaya’s medium with rock phosphate as the main ‘P’ source in the presence of ammonium sulphate. The fungus grew profusely in the medium by secreting oxalic acid which caused a reduction in the pH of the medium. To understand the mechanism behind the rock phosphate solubilization, an attempt was made to clone the fungal genomic DNA. In the Pikovskaya’s medium amended with rock phosphate, the clone MAP 22 released 80 μg/mL of P at the end of 24 h while, L. fraterna released 65 μg/mL of P at the end of 30 days incubation. We used HPTLC to confirm that oxalic acid is the main mineral-transforming agent that was secreted. The wild and the sub-clone MAP 22 released 1,490 and 2,950 μg/mL of oxalic acid, respectively. Therefore, it is possible to use the clone MAP 22 for more efficient inoculum production in vivo .