To prepare methanol extracts,10 g of lyophilized S. varians WT
or Mut was homogenized in100mL of methanol,and the mixture was stirred at 4 C in are frigerator.After 48 h,the homogenate was centrifuged(20,000g) at 4 C for 20 min to remove the
residue. The supernatant wasf iltered through a 0.45-mm filter
(Millipore Corporation,Billerica,MA,USA)and concentrated by rotary evaporation(EYELA,modelN-1001s-W;Tokyo,Japan).The
resulting methanol extracts were stored in are frigerator at 4 C
until further use.