Disruption of the gene encoding β-1, 3-glucanase in marine-derived Williopsis saturnus WC91-2 enhances its killer toxin activity

As the β-1, 3-glucanase produced by the marine-derived Williopsis saturnus WC91-2 could inhibit the activity of the killer toxin produced by the same yeast, the WsEXG1 gene encoding exo-β-1, 3-glucanase in W. saturnus WC91-2 was disrupted. The disruptant WC91-2-2 only produced a trace amount of β-1, 3-glucanase but had much higher activity of killer toxin than W. saturnus WC91-2. After the disruption of the WsEXG1 gene, the expression of the gene was significantly decreased from 100% in the cells of W. saturnus WC91-2 to 27% in the cells of the disruptant WC91-2-2 while the expression of the killer toxin gene in W. saturnus WC91-2 and the disruptant WC91-2-2 was almost the same. During 2-l fermentation, the disruptant WC91-2-2 could produce the highest amount of killer toxin (the size of the inhibition zone was 22 ± 0.7 mm) within 36 h when the cell growth reached the middle of the log phase.