Fig. 2

a: Schematic diagram of the heme synthesis pathway; b: Schematic diagram of the growth-coupled screening process and the designed ribosome binding site (RBS) library. Transcription of hemBCDEFY was initiated using two T7 promoters with four different intensities of RBS for each gene. B1–B4 represent the enhancement of strength, and the same for other genes. A darker color also represents an increase in intensity; c: RBS statistics for initial strains and strains following four rounds of subculture; d: PPIX production of initial strains and strains following four rounds of subculture in 96-well plates