Relationship Between Lignin Degradation and Production of Reduced Oxygen Species by Phanerochaete chrysosporium

Abstract

The relationship between the production of reduced oxygen species, hydrogen peroxide (H(2)O(2)), superoxide (O(2)), and hydroxyl radical (.OH), and the oxidation of synthetic lignin to CO(2) was studied in whole cultures of the white-rot fungus Phanerochaete chrysosporium Burds. The kinetics of the synthesis of H(2)O(2) coincided with the appearance of the ligninolytic system; also, H(2)O(2) production was markedly enhanced by growth under 100% O(2), mimicking the increase in ligninolytic activity characteristic of cultures grown under elevated oxygen tension. Lignin degradation by whole cultures was inhibited by a specific H(2)O(2) scavenger, catalase, implying a role for H(2)O(2) in the degradative process. Superoxide dismutase also inhibited lignin degradation, suggesting that O(2) is also involved in the breakdown of lignin. The production of .OH was assayed in whole cultures by a benzoate decarboxylation assay. Neither the kinetics of .OH synthesis nor the final activity of its producing system obtained under 100% O(2) correlated with that of the lignin-degrading system. However, lignin degradation was inhibited by compounds which react with .OH. It is concluded that H(2)O(2), and perhaps O(2), are involved in lignin degradation; because these species are relatively unreactive per se, their role must be indirect. Conclusions about a role for .OH in ligninolysis could not be reached.