초록
<P><B>Background</B></P><P><I>Trichoderma reesei is</I> a widely used industrial strain for cellulase production, but its low yield of β-glucosidase has prevented its industrial value. In the hydrolysis process of cellulolytic residues by <I>T. reesei</I>, a disaccharide known as cellobiose is produced and accumulates, which inhibits further cellulases production. This problem can be solved by adding β-glucosidase, which hydrolyzes cellobiose to glucose for fermentation. It is, therefore, of high vvalue to construct <I>T. reesei</I> strains which can produce sufficient β-glucosidase and other hydrolytic enzymes, especially when those enzymes are capable of tolerating extreme conditions such as high temperature and acidic or alkali pH.</P><P><B>Results</B></P><P>We successfully engineered a thermostable β-glucosidase gene from the fungus <I>Periconia sp.</I> into the genome of <I>T. reesei</I> QM9414 strain. The engineered <I>T. reesei</I> strain showed about 10.5-fold (23.9 IU/mg) higher β-glucosidase activity compared to the parent strain (2.2 IU/mg) after 24 h of incubation. The transformants also showed very high total cellulase activity (about 39.0 FPU/mg) at 24 h of incubation whereas the parent strain almost did not show any total cellulase activity at 24 h of incubation. The recombinant β-glucosidase showed to be thermotolerant and remains fully active after two-hour incubation at temperatures as high as 60°C. Additionally, it showed to be active at a wide pH range and maintains about 88% of its maximal activity after four-hour incubation at 25°C in a pH range from 3.0 to 9.0. Enzymatic hydrolysis assay using untreated, NaOH, or Organosolv pretreated barley straw as well as microcrystalline cellulose showed that the transformed <I>T. reesei</I> strains released more reducing sugars compared to the parental strain.</P><P><B>Conclusions</B></P><P>The recombinant <I>T. reesei</I> overexpressing <I>Periconia sp.</I> β-glucosidase in this study showed higher β-glucosidase and total cellulase activities within a shorter incubation time (24 h) as well as higher hydrolysis activity using biomass residues. These features suggest that the transformants can be used for β-glucosidase production as well as improving the biomass conversion using cellulases.</P>