Screening of marine fungi for lignocellulose-degrading enzyme activities

Twenty-nine fungal isolates collected from tropical and subtropical mangrove/marine habitats were screened for the presence of lignocellulose-degrading enzyme activities in agar media. These fungi were ascomycetes, except for a basidiomycete, Calathella mangrovei, and a mitosporic fungus, Cirrenalia tropicalis. Endoglucanase and xylanase were the most common enzymes produced. However, none of the fungi exhibited an ability to decolourise Poly-R-478 dye, indicating the lack of ligninolytic peroxidases. Three groups of fungi were categorised according to their cellulolytic, xylanolytic, and ligninolytic enzymes. Group I contained 21 isolates (ca. 72% of the test fungi) able to produce the three enzymes: endoglucanase, xylanase and laccase. Group II comprised 2 isolates lacking the ability to utilise filter paper and/or xylan, whereas Group III consisted of 6 isolates ( ca. 21%) with no laccase activity. Five laccase-producing isolates selected for growth on artificial seawater (ASW) agar supplemented with 2,2'-azino-bis-3-ethylbenzthiazoline- 6-sulfonic acid ( ABTS), a substrate for this enzyme, exhibited no laccase activity. Further testing in ASW liquid medium with Hypoxylon species B and Halorosellinia oceanica showed that laccase activity was detectable from culture supernatants that had been dialysed against distilled water. Therefore, care is required in assessing laccase activity when using an agar plate assay in the presence of ASW.