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).