Fig. 4
Application of promoter stnYp for indigoidine production. (A) Visual observation of indigoidine production on R5A agar medium from recombinant strain harboring indC gene under control of stnYp promoter and other promoters (ermEp*, kasOp* and SP44). The empty plasmid pSET152 was introduced into S. albus J1074 as a negative control. The plates were photographed every day in 5-day cultivation (1–5 days). Representative images of three independent experiments with similar results were shown. (B) Indigoidine production in R5A liquid media from recombinant strains (S. albus-ermEp*-indC, S. albus-kasOp*-indC, S. albus-SP44-indC, S. albus-stnYp-indC) harboring the indC gene under the control of ermEp*, kasOp*, SP44 and stnYp were monitored, and empty plasmid pSET152 was introduced into S. albus J1074 as a negative control. Indigoidine production was measured by detecting OD600 of the 10-fold diluted supernatant of fermentation cultures with DMSO. Fermentation was carried out for five days and the cultures were collected every day. Three independent experiments were carried out for each strain and all data were the average data. Statistical analyses were performed and marked (*, p ≤ 0.1; **, p ≤ 0.05; ***, p ≤ 0.01)