Disruption of the acid protease gene in Saccharomycopsis fibuligera A11 enhances amylolytic activity and stability as well as trehalose accumulation

The acid protease gene in Saccharomycopsis fibuligera A11 was disrupted by integrating the HPT (hygromycin B phosphotransferase) gene into ORF (Open Reading Frame) of the acid protease gene. The mutant 12 obtained could grow in the medium containing hygromycin. No clear zone formed by the mutant grown on the plate containing milk protein was observed whereas a big clear zone formed by the strain A11 was detected. The acid protease and amylases activities produced by the mutant within 3 days were 0.89 U/ml and 424.7 U/ml, respectively while those produced by the strain A11 were 13.5 U/ml and 259.9 U/ml, respectively. The amylases preparations produced by the mutant 12 and the strain A11 kept 88.8% and 45.5% of amylase activity, respectively after they were incubated at 37 °C for two days. Trehalose amount accumulated in the mutant cells was 28.3% (w/w) while that accumulated in the cells of S. fibuligera A11 was 23.6 (w/w).