Fungal degradation of pine and straw alkali lignins

Summary Kraft pine and straw lignins were fractionated into aqueous soluble and organic soluble-ether insoluble parts. Chemical analysis, UV characteristics, and gel permeation chromatograms of crude and fractionated lignins were studied. Using pure and mixed, N-limited and non N-limited standing cultures of several fungal species, the biodegradability of curde and fractionated lignins was compared. Straw lignins, especially the aqueous fraction were degraded by most of the fungi studied. Except for Sporotrichum pulverulentum, nitrogen limitation did not seem to favour degradation. The best fungi for degradation under conditions of N-limitation were S. pulverulentum, Humicola fuscoatra, and Aspergillus wentii, under sufficient nitrogen: A. wentii, Chaetomium cellulolyticum and H. fuscoatra. The greatest percentage degradation, 55%, was obtained with S. pulverulentum under nitrogen limited conditions from 1 gl^–1 organic soluble-ether insoluble kraft lignin. Gel chromatography showed that the degradation was over the complete molecular size range.