Construction of an Aspergillus oryzae △nptB△pyrG Host for Homologous Expression of Lipase and Catalytic Property Characterization of Recombinant Lipase

Aspergillus oryzae is an ideal cell factory for protein expression with powerful protein processing and secretion capabilities. The current study aimed to explore the homologous expression of A. oryzae lipase AOL (GenBank: KP975533) by constructing an auxotrophic A. oryzae △ pyrG △ nptB and subsequently characterizing the immobilization and catalytic properties of recombinant lipase. Initially, the pyrG gene knocked out in wild-type A. oryzae by homologous recombination, followed by the creation of a uridine/uracil auxotroph transformation. Through this system, the protease gene nptB was precisely knocked out, leading to a substantial decrease in extracellular (39.04%) and intracellular (90.07%) protease activity. The A. oryzae △ nptB △ pyrG strain was used as host for homologous expression of lipase AOL. After transformation of linearized lipase-expression cassette, the engineered A. oryzae AOL-8 was screened out with the lipase gene copy number of 14, exhibiting extracellular and intracellular lipase activities of 1.75 U/mL and 46.4 U/g, respectively. Subsequently, the production and immobilization of the recombinant lipase, via physical adsorption on macroporous resin XRZ04B, were achieved through submerged fermentation of the AOL-8 strain. The results of esterification catalytic properties of immobilized recombinant lipase indicated that the lipase exhibited optimal catalytic activity with lauric acid and methanol as substrates, a reaction temperature of 35 °C, and n-hexane as the preferred solvent medium; its highest conversion rate can reach at 72.3%.