Fig. 4

Optimisation of the HBA module with the new promoter library. Promoter fine-tuning of the HBA module. Six degenerate σ⁷⁰ promoters were selected for EcoFlex assembly with each pathway gene, E. coli DH10β was transformed and grown on 2YT agar with antibiotics for 3 days at 30 °C. Colonies with distinct yellow-orange colouration were grown and quantified for pathway intermediates as described in the methods. The low-strength pathway (J23114-RK) and an empty plasmid control (pTU1-A) were tested for relative comparison. Data and error bars (standard deviation) is representative of three biological repeats. Sequencing summary is provided in Additional file 1: Table S2