Fig. 4

Production of bottromycin A2 from 4-hydroxybenzoate (4HB) in S. lividans ΔYA8-DG2 using a fed-batch process with repeated substrate feeding. The data represent the mean values and standard deviations of three biological replicates (n = 3) (A). At the end of the process, the product was extracted from the culture broth using ethyl acetate and analysed for the presence of bottromycin A2 [M + H]⁺  = 823.453) and methylated bottromycin A2 [M + H]⁺  = 837.453) using LC–MS (B). A commercial bottromycin standard was analysed for comparison (C). As shown, a minor fraction of the methylated derivative was formed in addition to bottromycin A2