Upcycling whey through the production of edible <i>Aspergillus oryzae</i> cell biomass

Whey is a byproduct in the manufacturing of dairy products. Its use is limited, and its nutrients make it expensive for its disposal. Therefore, we attempted to develop its upcycling method. When the Aspergillus oryzae RIB40 strain was cultured in whey, more than 75% of lactose, its major saccharide, remained after 7 days of cultivation. However, when lactase preparation was added, most sugars were efficiently removed, implying that lactase is essential for consuming whey nutrients. We created an A. oryzae lactase-overexpressing strain by introducing the tef1 promoter and lactase gene into RIB40. When cultured in whey, the transformant completely consumed its saccharides. The biological oxygen demand, chemical oxygen demand, total nitrogen concentration, and total phosphorus concentration of the whey decreased by 90%, 91%, 62%, and 95%, respectively, through this fermentation. The transformant can be considered "self-cloning" and is not subject to regulations on recombinant organisms in countries including Japan.