Lycopene is a red carotenoid pigment with strong antioxidant activity. Saccharomyces cerevisiae is considered a promising host to produce lycopene, but lycopene toxicity is one of the limiting factors for high-level production. In this study, we used heterologous lycopene biosynthesis genes crtE and crtI from Xanthophyllomyces dendrorhous and crtB from Pantoea agglomerans for lycopene production in S. cerevisiae. The crtE, crtB, and crtI genes were integrated into the genome of S. cerevisiae CEN.PK2-1C strain, while deleting DPP1 and LPP1 genes to inhibit a competing pathway producing farnesol. Lycopene production was further improved by inhibiting ergosterol production via downregulation of ERG9 expression and by deleting ROX1 or MOT3 genes encoding transcriptional repressors for mevalonate and sterol biosynthetic pathways. To further increase lycopene production, CrtE and CrtB mutants with improved activities were isolated by directed evolution, and subsequently, the mutated genes were randomly integrated into the engineered lycopene-producing strains via delta-integration. To relieve lycopene toxicity by increasing unsaturated fatty acid content in cell membranes, the OLE1 gene encoding stearoyl-CoA 9-desaturase was overexpressed. In combination with the overexpression of STB5 gene encoding a transcription factor involved in NADPH production, the final strain produced up to 41.8 mg/gDCW of lycopene, which is approximately 74.6-fold higher than that produced in the initial strain.
Keywords: Delta-integration; Directed evolution; Lycopene; Ole1; Saccharomyces cerevisiae; Stb5.