Fig. 3

Control of spontaneous mutagenesis during the precursor toxicity-based screening. a, b Survival rates of DH10B- and LowMut-based positive a and negative b controls on the screening plate with 1 mM IPTG and a variation of mevalonate concentration. Survival rate was the ratio of colony forming units (CFUs) on the selected mevalonate concentration to CFUs on 0 mM mevalonate. Pie graphs in b represent the location of mutagenesis in the MBIS operon of 4 randomly selected colonies from each condition. White, no mutation in the MBIS operon; olive, ERG12; cyan, ERG8 (see the color scheme of Fig. 1a). c Recovery of LowMut-based positive control strains from a simulated mixture on the screening plate with 1 mM IPTG and 8 mM mevalonate. d Scheme of the second screening process using fresh LowMut pA5c–MBIS strain to exclude false positives that evade the precursor toxicity via spontaneous mutations (red crosses)