Fig. 3

Screening of 1-butanol production driven by the different FRE combinations. Strain ΔldhA ΔfrdBC ΔadhE Δpta was transformed with the three plasmids carrying the operon atoB-adhE2-crt-hbd, gene ter, and fdh expressed by the different FRE. Since each plasmid has four possible FRE to pair with, a total of (4 × 4 × 4) 64 combinations was resulted. Genotype (FRE::gene) of the three plasmids is boxed by gray borders on the top and on the left. Each unique FRE is highlighted by color blocks. The dot in the table indicates the specific plasmid (FRE::gene) combination harbored in each strain. Production results from the 64 different strains are grouped according to the FRE::fdh combination shown on the left. Cells were grown in TB medium aerobically to an OD₆₀₀ of about 4 then switched into anaerobic condition to induce 1-butanol fermentation. Samples were taken after 24 h of anaerobic switch