Fig. 3
Combinatorial modular pathway optimization for enhanced ethyl lactate biosynthesis by varying plasmid copy number. a Re-modularization of the ethyl lactate biosynthesis pathway. Pyruvate-to-lactate ester and ethanol modules were re-modulated into upstream and downstream modules using plasmids with different copy numbers. b Ethyl lactate production, c OD600, d Consumed glucose, e Acetate, f Lactate, g Ethanol, and h Ethyl acetate of EcJW106-108 and EcJW203-208 in high cell density cultures induced with various concentrations of IPTG. Green rectangle: low copy number plasmid (10); P15A: origin of pACYCDuet-1; blue rectangle: medium copy number plasmid (40); ColE1: origin of pETDuet-1; red rectangle: high copy number plasmid (100); RSF1030: origin of pRSFDuet-1; PT7: T7 promoter; TT7: T7 terminator. All of the strains were induced at 0 h with 0.01, 0.1, or 1.0 mM IPTG, respectively. Each error bar represents 1 s.d. (n = 3). Red arrows indicate the selected strain with an optimum concentration of IPTG for the further studies