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The Chemistry of Fungal Humic Acid-like Polymers and of Soil Humic Acids¹

ABSTRACT

A. niger, E. nigrum, and S. chartarum were grown in glucoseasparagine media according to Martin et al. The fungal "humic acids" synthesized were isolated, purified, and characterized by elementary and functional group analyses and by permanganate oxidation of methylated preparations. The oxidation products were separated by extraction into organic solvents, followed by preparative gas chromatography. The major components were identified by mass spectrometry and microinfrared spectrophotometry. The experimental data for the fungal "humic acids" were then compared with those obtained by identical methods on soil and peat humic acids.

There were a number of similarities in surface functional groups between the fungal and soil preparations. The major oxidation products from the fungal materials were: (i) aliphatic mono- and dicarboxylic acids; (ii) benzenecarboxylic acids; (iii) phenolic acids; and (iv) aromatic compounds containing S and N. Compared with peat and soil humic acids, the fungal materials produced, per gram of initial material, relatively small amounts of aromatic but more aliphatic compounds. The E. nigrum "humic acid" yielded substantial amounts of n-C₁₄ to n-C₁₈ fatty acids. The results show that fungal "humic acids" are complex organic materials containing aliphatic and aromatic structures, only some of which are phenolic. Claims by Martin et al. that simple phenols and phenolic acids were significant constituents of fungal "humic acids" were not confirmed.

¹ Contribution no. 429 from the Soil Research Institute, Canada Agr. Ottawa, Ont.

² Senior Research Scientist; Visiting Scientist from the Universidad Nacional del Sur, Bahia Blanca, Argentina; and Research Scientist, respectively. The authors thank G.F. Morris for elementary analyses.

Received for publication August 16, 1972. Accepted for publication October 12, 1972.