Disordered ultrastructure in lignin-peroxidase-secreting hyphae of the white-rot fungus Phanerochaete chrysosporium.

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.