The practice of exposing liquid cultures of the white-rot fungus Phanerochaete chrysosporium to a pure
oxygen atmosphere under conditions of nutrient
starvation has been widely adopted to induce
lignin peroxidase (LiP) synthesis. Transmission electron microscopy was used to examine hyphal cells of
carbon-limited cultures that had been exposed to an atmosphere of pure
oxygen, and revealed evidence of a major loss in organization of cellular ultrastructure, which may be attributed to
oxygen toxicity. Under some conditions (continuous agitation in air with
cellulose as the
carbon source) cultures will produce LiP without needing to be exposed to a pure
oxygen atmosphere. A similar major loss of cellular ultrastructure was found in hyphal cells from such cultures upon examination. Investigation of the levels of H2O2,
catalase and carbonyl content of intracellular
proteins suggests that the latter cultures developed a hyperoxidant state because the rate of supply of
carbon from
cellulose hydrolysis was insufficient for
oxygen homeostasis. The association of LiP with these cultures and with those exposed to an atmosphere of pure
oxygen infers that LiP may be triggered in response to
oxidant stress.