Novel sources of β-glucanase for the enzymatic degradation of schizophyllan

Schizophyllan is a homoglucan produced by the fungus Schizophyllum commune, with a β-1,3-linked backbone and β-1,6-linked side chains of single glucose units at every other residue. Schizophyllan is commercially produced for pharmaceutical and cosmetics uses. However, surprisingly little information is available on the biodegradation of schizophyllan. Enzymes that attack schizophyllan could be useful for controlled modifications of the polymer for novel applications. Enrichment cultures were used to isolate 20 novel fungal strains from soil samples, capable of growing on schizophyllan as a sole carbon source. Three additional strains were isolated as contaminants of stored schizophyllan solutions. Strains showing the highest levels of β-glucanase activity were identified as Penicillium simplicissimum, Penicillium crustosum, and Hypocrea nigricans. β-glucanases also showed activity against the similar β-glucans, laminarin and curdlan. By comparison, commercial β-glucanase from Trichoderma longibrachiatum and laminarinase from Trichoderma sp. showed lower specific activities toward schizophyllan than most of the novel isolates. β-glucanases from P. simplicissimum and H. nigricans exhibited temperature optima of 60 °C and 50 °C against schizophyllan, respectively, with broad pH optima around pH 5.0. Partial purifications of β-glucanase from P. simplicissimum and P. crustosum demonstrated the presence of multiple active endoglucanase species, including a 20–25 kD enzyme from P. simplicissimum.