Abstract
Zeaxanthin is vital to human health; thus, its production has received much attention, and it is also an essential precursor for the biosynthesis of other critical carotenoids such as astaxanthin and crocetin. Yarrowia lipolytica is one of the most intensively studied non-conventional yeasts and has been genetically engineered as a cell factory to produce carotenoids such as lycopene and β-carotene. However, zeaxanthin production by Y. lipolytica has not been well investigated. To fill this gap, β-carotene biosynthesis pathway has been first constructed in this study by the expression of genes, including crtE, crtB, crtI, and carRP. Three crtZ genes encoding β-carotene hydroxylase from different organisms were individually introduced into β-carotene-producing Y. lipolytica to evaluate their performance for producing zeaxanthin. The expression of crtZ from the bacterium Pantoea ananatis (formerly Erwinia uredovora, Eu-crtZ) resulted in the highest zeaxanthin titer and content on the basis of dry cell weight (DCW). After verifying the function of Eu-crtZ for producing zeaxanthin, the high-copy-number integration into the ribosomal DNA of Y. lipolytica led to a 4.02-fold increase in the titer of zeaxanthin and a 721% increase in the content of zeaxanthin. The highest zeaxanthin titer achieved 21.98 ± 1.80 mg/L by the strain grown on a yeast extract peptone dextrose (YPD)–rich medium. In contrast, the highest content of DCW reached 3.20 ± 0.11 mg/g using a synthetic yeast nitrogen base (YNB) medium to culture the cells. Over 18.0 g/L of citric acid was detected in the supernatant of the YPD medium at the end of cultivation. Furthermore, the zeaxanthin-producing strains still accumulated a large amount of lycopene and β-carotene. The results demonstrated the potential of a cell factory for zeaxanthin biosynthesis and opened up an avenue to engineer this host for the overproduction of carotenoids.
Highlights
Zeaxanthin is a C40 hydroxyl-carotenoid with a chemical structure that has an unsaturated polyene chain as a skeleton and two β-rings on each side of the skeleton with a hydroxyl-group located on the 3 site of each ring
To further enable the strain to biosynthesize β-carotene, the gene carRP was introduced into the lycopene-producing strain in this study (Velayos et al, 2000)
A zeaxanthin biosynthesis pathway was constructed in this study by the expression of crtE, crtB, crtI, carRP, and crtZ genes in non-carotenoid-producing Y. lipolytica
Summary
Zeaxanthin is a C40 hydroxyl-carotenoid with a chemical structure that has an unsaturated polyene chain as a skeleton and two β-rings on each side of the skeleton with a hydroxyl-group located on the 3 site of each ring. Zeaxanthin is Engineering Yeast for Zeaxanthin Production found in the human eyes, liver, kidneys, ovaries, and other organs. Zeaxanthin and its isomer, lutein, provide unique health benefits to the human macular region. These two carotenoids, including zeaxanthin and its isomer, lutein, greatly enrich the human retinal macula region to improve visual function, filter blue light, and prevent oxidative damage (Carpentier et al, 2009). These beneficial effects of zeaxanthin on human health led to the tremendous commercial value of zeaxanthin production
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