A new and unusual β-glucosidase from Aspergillus fumigatus : Catalytic activity at high temperatures and glucose tolerance

The demand for novel enzymes with the potential to catalyze reactions at high temperatures has encouraged the exploration of new thermophilic strains in recent years. Several fungal thermophilic β-glucosidases have been described previously. However, only a few β-glucosidases meet industrial requirements, such as hydrolytic activity at high temperatures and tolerance to glucose inhibition. Because tropical areas support high species diversity, the Atlantic Forest biome can offer great opportunities for bioprospecting new β-glucosidase producers to fulfill industrial needs. This study reports the production and biochemical characterization of an unusual thermophilic β-glucosidase produced by an Aspergillus fumigatus strain isolated from the Atlantic Forest biome. This enzyme can be produced using a low-cost cultivation medium with canola meal as the substrate. The highest β-glucosidase production (24.53 U/mL) was obtained when the fungus was cultivated in 2.9% canola meal over a period of 101 h at pH 4.2, and a temperature of 40 °C. This enzyme has an optimum temperature of 80 °C, which is higher than that of almost all its known fungal counterparts. Moreover, it is highly glucose tolerant, unlike other β-glucosidases that are inhibited by this sugar, with an inhibitory constant (Ki) of 543 mM. The combination of these attributes and their sustained activity at 80 °C distinguishes this enzyme from other A. fumigatus enzymes and almost every other β-glucosidase characterized from thermotolerant fungal species described to date. Therefore, this novel enzyme is a promising target for bioethanol production.