Phenotype characterization
Cell samples from cultures in duplicate or triplicate shake flasks were collected at various time points throughout the fermentation. Dry cell weight (DCW) in 3 mL culture was measured after filtration for monitoring cell growth. The concentration of residual glucose in culture was determined by salicylic acid method (Zou, Hang, Chu, Zhuang, & Zhang, 2009b). The erythromycin titer was measured by the modified colorimetric method (Zou et al., 2009a).