Colony formation under varied nutritional conditions. E. coli cells carrying the synthetic dual operon preliminarily grown under IPTG-free (a) and IPTG-supplied (30 μM IPTG, (b)) conditions were inoculated onto M63 agar plates containing 15 μM IPTG with different amino acid contents. The newly formed single colonies were observed by fluorescence microscopy after 3–5 days of incubation. NIBA and WIG are described in Figure 3. PH and Merge indicate the phase-contrast and merged images of NIBA and WIG, respectively. The final concentrations of amino acids were all 1 mM. + and − indicate the presence and absence of leucine (Leu) and histidine (His), respectively.
