EXTRACELLULAR OXIDATIVE-ENZYMES OF COAL-ATTACKING FUNGI

The participation of extracellular oxidative enzymes, as known from li gnin degraders, in fungal coal degradation is demonstrated and discuss ed in this paper. Two basidiomycete strains that are able to solubiliz e German lignite (brown coal) were isolated and characterized accordin g to their enzymology. One of them (strain RES Ik) produces extracellu lar Mn-peroxidase, the other (strain RES Ib) excretes two oxidative en zymes with laccase and peroxidase activity. These enzymes were excrete d shortly before the beginning of coal solubilization. Different coal substances can affect the production of these exoenzymes. The producti on of extracellular peroxidase by strain RES Ik can be induced by the addition of native lignite powder or different lignite fractions (bitu men, matrix and humic acids) to the culture medium. Fungal growth was enhanced under these culture conditions, too. On the other hand, produ ction of extracellular laccase activity by strain RES Ib can be stimul ated by the addition of water-soluble humic acids, too, but is inhibit ed by the addition of other coal fractions (bitumen and matrix) or by native lignite powder, In the direct neighbourhood of lignite pieces t he fungal surface cultures of the basidiomycete RES Ik show guttation. The drops are dark brown colored and contain strong peroxidase activi ty (up to 300 U/ml). But this cellfree solution is not able to solubil ize coal, alone. The fungus RES Ik possesses enzymatic capacities for modifying the structure of coal-derived humic acids. The strain can me tabolize these alkali-soluble coal macromolecules under cometabolic co nditions by simultaneous excretion of peroxidase, which probably is in volved in the degradation process. In vitro-tests with the cellfree pe roxidase (RES Ik) or laccase (RES Ib), purified by affinity chromatogr aphy, could not demonstrate the ability of these enzymes to promote wa ter solubility of low rank coals, alone. (C) 1997 Elsevier Science B.V .