Heterologous expression system of Aspergillus oryzae strain isolated from Korean traditional fermented foods

Sang-Cheol Jun Bo-Han Zhu Jong-Hwa Kim Kap-Hoon Han
Department of Pharmaceutical Engineering, Woosuk University, Wanju, South Korea

It is important to find an efficient way to amplify the expression of heterologous gene(s) of interest in a fungal expression system for giving the high potential of fungi as genetic resources. Also, mass production systems of foreign protein is important for bio-industry, including pharmaceutical engineering and functional foods production. In addition, for ensuring the safety of the products, it is highly suggested to use GRAS (Generally Recognized As Safe) strain as a host. Here, we constructed a heterologous gene expression system for producing foreign gene product including bacterial origin one such as bacterial β-glucosidase. The produced β-glucosidase is a hydrolytic enzyme and the expression of the gene was stimulated by placing it under the control of the constitutively activated gpdA gene promoter or threonine-inducing alcA gene promoter of Aspergillus nidulans. The pyrithiamine-resistant gene, ptrA, was used as the selection marker for Aspergillus transformation. The signal peptide of A. oryzae α-amylase AmyB was linked to the N-terminus of the bacterial β-glucosidase protein, and 3X FLAG was tagged at the C-terminus. The fungal transformants successfully overexpressed the β-glucosidase gene and expression level was monitored by western blot analysis with anti-FLAG antibody. The functional activity of the protein was detected by esculin converting test. The expression system of A. oryzae could be beneficial for industrial applications.