Cells cultivated in YG2 medium for 36 h were centrifuged at 8000 g for 10 min. The cell pellets were washed two times with 50 mM potassium phosphate buffer, pH 6.0 (KPB buffer: 4 ml of 1MKH2PO4 and 46 ml of 1 M K2HPO43H2O mixed with sterile distilled water to 1000 ml) and resuspended in the same buffer