Heterologously expressed Aspergillus aculeatus β-glucosidase in Saccharomyces cerevisiae is a cost-effective alternative to commercial supplementation of β-glucosidase in industrial ethanol production using Trichoderma reesei cellulases

Abstract

Trichoderma reesei is a filamentous organism that secretes enzymes capable of degrading cellulose to cellobiose. The culture supernatant of T.reesei, however, lacks sufficient activity to convert cellobiose to glucose using β-glucosidase (BGL1). In this study, we identified a BGL (Cel3B) from T.reesei (TrCel3B) and compared it with the active β-glucosidases from Aspergillus aculeatus (AaBGL1). AaBGL1 showed higher stability and conversion of sugars to ethanol compared to TrCel3B, and therefore we chose to express this recombinant protein for use in fermentation processes. We expressed the recombinant protein in the yeast Saccharomyces cerevisiae, combined it with the superb T.reesei cellulase machinery and used the combination in a simultaneous saccharification and fermentation (SSF) process, with the hope that the recombinant would supplement the BGL activity. As the sugars were processed, the yeast immediately converted them to ethanol, thereby eliminating the problem posed by end product inhibition. Recombinant AaBGL1 activity was compared with Novozyme 188, a commercially available supplement for BGL activity. Our results show that the recombinant protein is as effective as the commercial supplement and can process sugars with equal efficiency. Expression of AaBGL1 in S.cerevisiae increased ethanol production effectively. Thus, heterologous expression of AaBGL1 in S.cerevisiae is a cost-effective and efficient process for the bioconversion of ethanol from lignocellulosic biomass.