Strong promoters might not be optimal to obtain maximum metabolic flux towards desired products, whereas modulating gene expression with multiple regulatory parts is an option to obtain optimal expression strength. Therefore, we assessed the difference of impact on beta-carotene production between modulating isoprenoid gene expression with multiple regulatory parts and strong promoter, to improve beta-carotene production through combined modulation of essential isoprenoid genes. Eight isoprenoid genes were modulated with six artificial regulatory parts having a wide range of strengths to assess their effects on beta-carotene production. Optimal strength for each isoprenoid gene expression was identified, leading to 1.2 to 3.5-fold increase in beta-carotene production. In contrast to previous reports, our work suggests that modulating dxr, ispG and ispH genes with appropriate strengths increase beta-carotene production. Beta-carotene yield reached 17.59 mg/g after combined modulation of dxs and idi genes, 8-fold higher than that of the parent strain. Modulating gene expression with multiple regulatory parts was better than strong promoter, providing a new gene modulation strategy for targeted biosynthesis.
Escherichia coli ; genetics ; metabolism ; Gene Expression Regulation ; Promoter Regions, Genetic ; Terpenes ; metabolism ; beta Carotene ; biosynthesis

β-carotene belongs to carotenoids family, widely applied in pharmaceuticals, neutraceuticals, cosmetics and food industries. In this study, three key genes (dxs, idi, and crt operon) within β-carotene synthetic pathway in recombinant Escherichia coli strain CAR005 were modulated with RBS Library to improve β-carotene production. There were 7%, 11% and 17% increase of β-carotene yield respectively after modulating dxs, idi and crt operon genes with RBS Library, demonstrating that modulating gene expression with regulatory parts libraries would have more opportunities to obtain optimal production of target compound. Combined modulation of crt operon, dxs and idi genes led to 35% increase of β-carotene yield compared to parent strain CAR005. The optimal gene expression strength identified in single gene modulation would not be the optimal strength when used in combined modulation. Our study provides a new strategy for improving production of target compound through modulation of gene expression.
Escherichia coli ; metabolism ; Gene Expression ; Gene Library ; Operon ; beta Carotene ; biosynthesis

β-carotene has a wide range of application in food, pharmaceutical and cosmetic industries. For microbial production of β-carotene in Saccharomyces cerevisiae, the supply of geranylgeranyl diphosphate (GGPP) was firstly increased in S. cerevisiae BY4742 to obtain strain BY4742-T2 through over-expressing truncated 3-hydroxy-3-methylglutaryl-CoA reductase (tHMGR), which is the major rate-limiting enzyme in the mevalonate (MVA) pathway, and GGPP synthase (GGPS), which is a key enzyme in the diterpenoid synthetic pathway. The β-carotene synthetic genes of Pantoea agglomerans and Xanthophyllomyces dendrorhous were further integrated into strain BY4742-T2 for comparing β-carotene production. Over-expression of tHMGR and GGPS genes led to 26.0-fold increase of β-carotene production. In addition, genes from X. dendrorhous was more efficient than those from P. agglomerans for β-carotene production in S. cerevisiae. Strain BW02 was obtained which produced 1.56 mg/g (dry cell weight) β-carotene, which could be used further for constructing cell factories for β-carotene production.
Basidiomycota ; enzymology ; Farnesyltranstransferase ; genetics ; metabolism ; Hydroxymethylglutaryl CoA Reductases ; genetics ; metabolism ; Metabolic Engineering ; Polyisoprenyl Phosphates ; Saccharomyces cerevisiae ; metabolism ; beta Carotene ; biosynthesis

Blakeslea trispora is a natural source of carotenoids, including β-carotene and lycopene, which have industrial applications. Therefore, classical selective breeding techniques have been applied to generate strains with increased productivity, and microencapsulated β-carotene preparation has been used in food industry (Li et al., 2019). In B. trispora, lycopene is synthesized via the mevalonate pathway (Venkateshwaran et al., 2015). Lycopene cyclase, which is one of the key enzymes in this pathway, is a bifunctional enzyme that can catalyze the cyclization of lycopene to produce β-carotene and exhibit phytoene synthase activity (He et al., 2017).
Citric Acid Cycle ; Fermentation ; Gas Chromatography-Mass Spectrometry/methods* ; Lycopene/metabolism* ; Mucorales/metabolism* ; Nicotine/pharmacology* ; beta Carotene/biosynthesis*