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 (H2O2), superoxide and hydroxyl radical (.OH), and the oxidation of synthetic lignin to CO2 was studied in whole cultures of the white-rot fungus Phanerochaete chrysosporium Burds. The kinetics of the synthesis of H2O2 coincided with the appearance of the ligninolytic system; also, H2O2 production was markedly enhanced by growth under 100% O2, mimicking the increase in ligninolytic activity characteristic of cultures grown under elevated oxygen tension. Lignin degradation by whole cultures was inhibited by a specific H2O2 scavenger, catalase, implying a role for H2O2 in the degradative process. Superoxide dismutase also inhibited lignin degradation, suggesting that superoxide 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% O2 correlated with that of the lignin-degrading system. However, lignin degradation was inhibited by compounds which react with .OH. It is concluded that H2O2, and perhaps superoxide, 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.