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  • Title: High level production of β-galactosidase exhibiting excellent milk-lactose degradation ability from Aspergillus oryzae by codon and fermentation optimization.
    Author: Zhao Q, Liu F, Hou Z, Yuan C, Zhu X.
    Journal: Appl Biochem Biotechnol; 2014 Mar; 172(6):2787-99. PubMed ID: 24435763.
    Abstract:
    A β-galactosidase gene from Aspergillus oryzae was engineered utilizing codon usage optimization to be constitutively and highly expressed in the Pichia pastoris SMD1168H strain in a high-cell-density fermentation. After fermentation for 96 h in a 50-L fermentor using glucose and glycerol as combined carbon sources, the recombinant enzyme in the culture supernatant had an activity of 4,239.07 U mL(-1) with o-nitrophenyl-β-D-galactopyranoside as the substrate, and produced a total of extracellular protein content of 7.267 g L(-1) in which the target protein (6.24 g L(-1)) occupied approximately 86 %. The recombinant β-galactosidase exhibited an excellent lactose hydrolysis ability. With 1,000 U of the enzyme in 100 mL milk, 92.44 % lactose was degraded within 24 h at 60 °C, and the enzyme could also accomplish the hydrolysis at low temperatures of 37, 25, and 10 °C. Thus, this engineered strain had significantly higher fermentation level of A. oryzae lactase than that before optimization and the β-galactosidase may have a good application potential in whey and milk industries.
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