FUNGAL ATTACK ON COAL II - SOLUBILIZATION OF LOW-RANK COAL BY FILAMENTOUS FUNGI

The solubilization of low-rank coal by fungi is not accompanied by its depolymerization, which was proven by several screening programs, A t otal number of 728 fungal strains were yet tested for solubilizing a G erman low-rank coal (lignite). The coal were used oxidatively pretreat ed (3% H2O2) and natively. During the first screening, the nitrogen co ntent of the media were reduced to select fungi, which solubilize coal under nitrogen-limited conditions. Among 480 micromycetous fungi test ed, at least ten strains were able to solubilize native low-rank coal pieces on a nitrogen-reduced agar-medium. They all belong to the conid iospores forming deuteromycetes (molds). Under 'solubilizing' conditio ns, only two of these ten strains showed weak extracellular activities (oxidases, peroxidases) toward 2,2'-azinobis(3-ethylbenzthiazoline-6- sulphonate) [ABTS]. In a second screening, 256 wood and litter decayin g basidiomycetes, above all white-rot fungi, were tested for their abi lity to solubilize low-rank coal under ligninolytic conditions; not an y strain was able to form black coal droplets or conspicuous diffusion areas. By using a nitrogen-rich medium, a few basidiomycetes showed a lso coal solubilizing activities, however, their ligninolytic enzymes were inhibited. The 'typical' solubilization of low-rank coal (formati on of black liquids from solid coal particles) by molds depends mainly on the nitrogen content of the medium (resulting in higher pH values) as well as on the oxidation grade of coal (e.g. H2O2-pretreatment). E xtracellular oxidases and peroxidases, both ligninolytic and nonlignin olytic ones, seem to play a minor, (or not any), role for this process . (C) 1997 Elsevier Science B.V.