Cell-free supernatant was obtained by centrifuging the culture broth at 2000 g, 30min,
4 C. The supernatantwas dialyzed across amembrane with a 10 kDa molecularweight cut-off against 20mMsodium acetate buffer (Ajax Finechem Pty Ltd, Australia), pH 5.0 at ten times of supernatant volume. The buffer was changed every 6 h until 24 h and the dialyzed
culture fluid was freeze-dried.