Type 2 IDI performs better than type 1 for improving lycopene production in metabolically engineered E. coli strains

In this study a comparison was made between type 1 and type 2 isopentenyl diphosphate isomerases (IDI) in improving lycopene production in Escherichia coli. The corresponding genes of Bacillus licheniformis and the host (i Bl and i Ec , respectively) were expressed in lycopene producing E. coli strains by pTlyciBl and pTlyciEc plasmids, under the control of tac promoter. The results showed that the overexpression of i Ec improved the lycopene production from 33 ± 1 in E. coli Tlyc to 68 ± 3 mg/gDCW in E. coli TlyciEc. In contrast, the expression of i Bl increased the lycopene production more efficiently up to 80 ± 9 mg/gDCW in E. coli TlyciBl. The introduction of a heterologous mevalonate pathway to elevate the IPP abundance resulted in a lycopene production up to 132 ± 5 mg/gDCW with i Ec in E. coli TlyciEc-mev and 181 ± 9 mg/gDCW with i Bl in E. coli TlyciBl-mev, that is, 4 and 5.6 times respectively. When fructose, mannose, arabinose, and acetate were each used as an auxiliary substrate with glycerol, lycopene production was inhibited by different extents. Among auxiliary substrates tested, only citrate was an improving one for lycopene production in all strains with a maximum of 198 ± 3 mg/gDCW in E. coli TlyciBl-mev. It may be concluded that the type 2 IDI performs better than the type 1 in metabolic engineering attempts for isoprenoid production in E. coli. In addition, the metabolic engineering of citrate pathway seems a promising approach to have more isoprenoid accumulation in E. coli.