Phenotypes of E3 and NRRL23338
Phenotypes of NRRL23338 and E3 were compared on agar medium and in liquid culture with glucose as a carbon source. With respect to the glossy colonies of NRRL23338 on agar medium, E3 produced gray spores more intensively (Fig. 1a). In order to show the exclusive effects of genome mutation on phenotypes as clear as possible, batch cultivation ofS. erythraea in a minimal liquid medium was performed (Hopwood, 1985). The growth rate of E3 was reduced by 14% compared to NRRL23338, and the biomass formation of E3 was decreased by approximately 18% (Fig. 1b). Both strains showed a two-step diauxic growth in the minimal medium, with growth suspension happening approximately at 30 h (Marcellin et al., 2013) followed by a growth slowdown until 45 h. The glucose consumption rate of E3 also decreased markedly compared to NRRL23338 (Fig. 1c). Approximately 450 mg/L of erythromycin was produced by E3 in the liquid culture, whereas NRRL23338 produced only 20 mg/L (Fig. 1d). Regarding the production of the diffusible pigment (Cortés et al., 2002), NRRL23338 colonies appeared more reddish by excreting more pigment out of the cells than retaining it within (Fig. 1a). The reddish pigment 7-O-rahmnosyl flaviolin is a kind of secondary metabolite, which is derived from malonyl-CoA (Cortés et al., 2002).