A high-throughput screening method for identifying lycopene-overproducing E. coli strain based on an antioxidant capacity assay

A straightforward, high-throughput screening method for identifying recombinant Escherichia coli strains that yield high levels of lycopene was developed based on the antioxidative properties of lycopene. Twenty-four recombinant E. coli strains were constructed using plasmids with various orderings of lycopene biosynthesis genes, Shine-Dalgarno regions, and aligned spacing regions. The high-throughput screening was based on antioxidant capacity measurements; we assessed the 2,2-diphenyl-1-picrylhydrazyl method, reducing activity method, and hydroxyl free radical scavenging method; the hydroxyl free radical scavenging method was determined to be the most suitable for use with our lycopene-overproducing system. The accuracy of this method was comparable to that of assay by high-performance liquid chromatography. The strain E. coli IEB11, which had the strongest antioxidant capacity and the highest lycopene-accumulating capacity, was selected and investigated for its ability to produce lycopene at different temperatures, glycerol concentrations, and fermentation times. In the optimal conditions in a 5-L fermenter, lycopene content of 1288 mg/L and a mean productivity of 53.7 mg/L/h were obtained after 24 h.