Continuous ethanol fermentation was performed in a tower- shaped reactor with a working volume of 450 mL, as previously described (Tang et al., 2006). Before fermentation, the reactor was sterilized by circulating 2 mg/L of NaClO solution overnight, and then sterilized tap water was supplied continuously for 1 day. Approximately 450 mL of pre-cultivated broth (containing 1.5 × 108 cells/mL) was inoculated into the reactor, and then sweet sorghum juice was fed into the reactor at a dilution rate of 0.15 h−1. Before feeding sweet sorghum juice into the reactor, the total sugar content