Laccase activity of lignicolous aquatic hyphomycetes isolated from the River Nile in Egypt

Eleven species of aquatic hyphomycetes were isolated from 92 samples of different lignin sources (unidentified wood segments, skeleton and neck of leaves, bark). The most common species were Pyramidospora casuarina (on 3.7% of samples), Triscelophorus monosporus (3.2%) and Flagellospora curvula (3%). Varying levels of laccase activity were present in most of the fungi included in this study. The laccase plate assay was found to be much less reliable than the spectrophotometric assay. Several factors including type of growth medium, the media pH and assay pH had marked effects on laccase activity. A few species produced high levels of laccase in both malt extract (ME) medium and low N medium; however, a majority of the species produced laccase in low nitrogen (N) medium (pH 4.5) but not in the ME medium. When the tested species were grown in low N medium at pH 4.5, six species showed acidic laccase (pH 4.5) activity; of these, four also showed alkaline laccase (pH 8.2) activity. Alatospora acuminata and Tetracladium marchalianum exhibited laccase activity only when grown in the low N medium at pH 8.2. These results indicate that aquatic hyphomycetes may play a role in the decomposition of lignin materials in freshwater environments.