Formation of Humic Acid Like Compounds by the Ectomycorrhizal Fungus, Pisolithus tinctorius 1

Formation of organic compounds by the ectomycorrhizal fungus, Pisolithus tinctorius, was studied to establish the relationship of these microbial products to humic and fulvic acids. The fungus was grown in a Melins-Norkrans liquid culture with either sucrose or a mixture of L-malic and L-succinic acid as the C and energy source. The biologically synthesized substances were characterized by chemical and infrared analyses. The fungus grown on the malic-succinic acid medium produced a black substance, whereas the organism grown on sucrose yielded only small amounts of a greenish-brown colored compound. The greenish-brown substance behaved similarly to fulvic and humic acids, when subjected to fractionation procedures using NaOH and HCl. The fraction soluble in base and acid had an infrared spectrum resembling that of fulvic acids. The fraction soluble in NaOH but insoluble in HCl had infrared features of humic acid. The black substance was insoluble in NaOH and HCl, and identification of infrared spectra revealed the black colored product to be uronic acids.