A high degree of lipid oxidative damage was detected in manganese-deficient lignin peroxidase (LIP)-producing cultures of Phanerochaete chrysosporium, indicating intensive exposure to high concentrations of reactive oxygen species (ROS), as is typically found in oxygenated LIP-producing cultures. The absence of manganese ions (Mn2+) in the cultures prevented activation of the manganese-containing antioxidant enzyme superoxide dismutase (MnSOD), but not MnSOD1 transcription and translation. In contrast, catalase activity was stimulated. In addition, the concentration of superoxide anions was enhanced and that of hydrogen peroxide was reduced, relative to Mn2+-containing control (non-LIP-producing) cultures. Significantly higher gene expression of the LIP-H2 isozyme was obtained in Mn2+-deficient cultures than in control cultures. The hydroxyl radical scavenger, dimethyl sulfoxide (DMSO; 50 mM), added to the culture every 12 h, completely abolished LIP expression at the mRNA and protein levels. These results indicate the involvement of ROS in LIP gene induction in Mn2+-deficient cultures, probably hydroxyl radicals (OH center dot) as was found in oxygenated cultures. However, the sources of ROS in general, and OH center dot, in particular, are probably different in each of the LIP-producing cultures. These observations reconfirm the hypothesis that the induction of LIP expression is at least partially mediated by the intracellular formation of ROS. (c) 2005 Elsevier Inc. All rights reserved.