Identification of genes affecting lycopene accumulation in Escherichia coli using a shot-gun method

Genes enhancing lycopene production in Escherichia coli were identified through colorimetric screening of shot-gun library clones constructed with E. coli chromosomal DNA. These E. coli cells had been engineered to produce lycopene, a red-colored carotenoid, which enabled screening for genes that enhance lycopene production. Six clones with enhanced lycopene production were isolated. Among 13 genes in these clones, dxs, appY, crl, and rpoS were found to be involved in enhanced lycopene production. While dxs and rpoS have been already reported to enhance lycopene production, appY and crl have not. DXP (1-deoxy-D-xylulose-5-phosphate) synthase is encoded by dxs and participates in the rate-limiting step in the synthesis of isopentenyl pyrophosphate (IPP), a building block of lycopene. Sigma S factor, encoded by rpoS, regulates transcription of genes induced at the stationary phase. The appY and crl genes encode transcriptional regulators related to anaerobic energy metabolism and the formation of curli surface fibers, respectively. E. coli harboring appY plasmids produced 2.8 mg lycopene/g dry cell weight (DCW), the same amount obtained with dxs despite the fact that appY is not directly involved in the lycopene synthesis pathway. The co-expression of appY, crl, and rpoS with dxs synergistically enhanced lycopene production. The co-expression of appY with dxs produced eight times the amount of lycopene (4.7 mg/g DCW) that was produced without expression of both genes (0.6 mg/g DCW).