13C NMR spectroscopic analysis of soil humic acids recovered after incubation with some white rot fungi and actinomycetes

Culture media containing soil humic acids were inoculated with either white-rot fungi (Phanerochaete chrysosporium and Trametes versicolor) or actinomycetes (Streptomyces viridosporus and Streptomyces sp.) and incubated until a loss of about 30% of humic acids had occurred in the growth medium. The humic acids were recovered by the use of a metal chelate affinity procedure and studied by 13C NMR spectroscopy in order to collect more information about the mechanism of attack on humic acids. The spectra resulting from fungal activity were the most modified; however, no important changes in the main constituents of these compounds and no increase in carboxyl content were recorded. The results suggest an unusual degradation process.