Screening of Filamentous Fungi for Xylanases and Cellulases Not Inhibited by Xylose and Glucose

Aims: Screening different filamentous fungi for thermostable xylanases and cellulases that would not be inhibited by xylose and glucose, respectively.

Methodology: Samples of fungi collected in the Atlantic forest region, Minas Gerais, Brazil, and some fungi from our Culture Collection were used in this screening. All fungi were grown in liquid media containing 1% sugar cane bagasse (SCB). After that, an aliquot of the crude broth was incubated at different temperatures (from 4 to 60 °C) in carboxymethyl cellulose (CMC) or xylan-media plates, for 12 hours. After this period, the plates were stained with Congo Red. Fungi that presented the best results (larger halos) were tested for the effect of adding xylose and glucose in the xylanase and cellulases activities, respectively. Crude extracts obtained from fungi grown in SCB were used for laccase and lichenase assay.

Results: The screening on agar plates with CMC/xylan presented halos of different sizes. From all tested fungi, the best cellulase producer was Malbranchea pulchella, which also presented the most thermostable xylanase. Penicillium griseofulvum presented bigger halos at all temperatures tested, but the xylanase lost almost 14% of its stability in higher temperatures. The effect of xylose and glucose on the enzymatic activities recorded dose-dependent. It was observed that 20% activation of the enzymes produced by M. pulchella with 30 mM glucose or 20 mM xylose to cellulase and xylanase, respectively. It was observed a loss of less than 20% for P. griseofulvum xylolytic activity using 50 mM xylose. Lichenase was detected in some fungi prospected but laccase was not detected.

Conclusion: Malbranchea pulchella was a good producer of xylanase and cellulase tolerant to xylose and glucose, respectively. Other studies must be performed with this fungus so that it can be used in the future for biotechnological purposes.