β-1,3-Glucanase Inhibits Activity of the Killer Toxin Produced by the Marine-Derived Yeast Williopsis saturnus WC91-2

The marine-derived Williopsis saturnus WC91-2 was found to produce very high killer toxin activity against the pathogenic yeast Metschnikowia bicuspidata WCY isolated from the diseased crab. It is interesting to observe that the purified beta-1,3-glucanase from W. saturnus WC91-2 had no killer toxin activity but could inhibit activity of the WC91-2 toxin produced by the same yeast. In contrast, the WC91-2 toxin produced had no beta-1,3-glucanase activity. We found that the mechanisms of the inhibition may be that the beta-1,3-glucanase competed for binding to beta-1,3-glucan on the sensitive yeast cell wall with the WC91-2 toxin, causing decrease in the amount of the WC91-2 toxin bound to beta-1,3-glucan on the sensitive yeast cell wall and the activity of the WC91-2 toxin against the sensitive yeast cells. In order to make W. saturnus WC91-2 produce high activity of the WC91-2 toxin against the yeast disease in crab, it is necessary to delete the gene encoding beta-1,3-glucanase.