2.4 Transformation of B. subtilis
The B. subtilis SCK6 strain was inoculated into 4 ml of YN medium with 5 mg/L erythromycin in a test tube. The cells were cultivated at 37 °C with shaking at 220 rpm overnight (~12 h). The culture was diluted to an optical density at 600 nm (OD600) of 1.0 in a fresh YN medium containing 1.5 % (w/v) xylose and then was grown for 2 h. The resulting cell culture was ready to be transformed. 100 ng of DNA was mixed with different volumes of the supercompetent cells in a 1.5-ml eppendorf tube and cultivated at 37 °C with shaking at 220 rpm for 90 min.