Hyphal sheath formation and iron-chelator production by liquid cultures of the brown rot fungi Gloeophyllum trabeum and Postia placenta were monitored over time. The effects of incubation at various temperatures, pH's and concentrations of iron, manganese and nitrogen were determined. Hyphal sheath production was observed microscopically and quantified with JAVA video analysis. The hyphal sheath was found on young and rejuvenated hyphae around the growing points and along the length of hyphae but not on the necrotic hyphae. Sheath formation was first detected after 4-6 days growth and increased until day 15. Sheath production was significantly greater in fungi growing at low concentrations of metals (0-50 µM iron or manganese) than in fungigrowing under other conditions. Increasing nitrogen concentration was correlated with decreased sheath production in Gloeophyllum trabeum. Iron-chelator production, as monitored by the chrome azurol S (CAS) assay, did not occur in detectable quantities until 3 weeks after inoculation. Iron-chelator production correlated with low concentrations of metals, but was not influenced by the sources or types of nitrogen. High levels of manganese (1000 µM) and iron (200 µM) repressed both iron-chelator production and hyphal sheath formation. Temperature and pH influenced the formation of hyphal sheath and iron-chelator production by both brown rot fungi. Gloeophyllum trabeum produced more hyphal sheath in pH 3.5 at 35°C than in the other conditions tested. Postia placenta yielded more sheath in pH 4.5 at 25°C than under other conditions.No significant relationship was observed between pH and the production of iron-chelator. Hyphal sheath formation and iron-chelator production have previously been implicated in the process of wood degradation by basidiomycetes.

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