Characterization of lycopene-overproducing E. coli strains in high cell density fermentations.

Previous work identified two recombinant strains of Escherichia coli capable of significant lycopene overproduction. These strains were constructed by superimposing the deletion of three genes, selected through combinatorial and systematic searches of the metabolic landscape, onto a previously engineered strain over-expressing critical genes in the lycopene biosynthesis pathway. In this paper, we characterize the performance of these two strains in comparison to the parental, pre-engineered strain. Specifically, high cell density fermentations were performed after identifying optimized putative operating parameters. High oxygen levels and increased pH values were found to be critical for increasing both specific and volumetric product titers. Carbon balances suggest linkages between glutamate, NADPH, formate, and alanine levels with lycopene overproduction. Furthermore, lycopene production reached nearly 220 mg/l from approximately 27 g dry cell weight/l in these reactors, which is the highest value reported to date for E. coli.