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Abstract
BackgroundRed yeast, Xanthophyllomyces dendrorhous (Phaffia rhodozyma) is the only yeast known to produce astaxanthin, an anti-oxidant isoprenoid (carotenoid) that is widely used in the aquaculture, food, pharmaceutical and cosmetic industries. Recently, the potential of this microorganism as a platform cell factory for isoprenoid production has been recognized because of high flux through its native terpene pathway. Addition of mevalonate, the common precursor for isoprenoid biosynthesis, has been shown to be critical to enhance the astaxanthin content in X. dendrorhous. However, addition of mevalonate is unrealistic during industrial isoprenoid production because it is an unstable and costly chemical. Therefore, up-regulating the intracellular mevalonate supply by enhancing the mevalonate synthetic pathway though genetic engineering is a promising strategy to improve isoprenoid production in X. dendrorhous. However, a system to strongly express multiple genes has been poorly developed for X. dendrorhous.ResultsHere, we developed a multiple gene expression system using plasmids containing three strong promoters in X. dendrorhous (actin, alcohol dehydrogenase and triose-phosphate isomerase) and their terminators. Using this system, three mevalonate synthetic pathway genes encoding acetoacetyl-CoA thiolase, HMG-CoA synthase and HMG-CoA reductase were overexpressed at the same time. This triple overexpressing strain showed an increase in astaxanthin production compared with each single overexpressing strain. Additionally, this triple overexpression of mevalonate synthetic pathway genes together with genes involved in β-carotene and astaxanthin synthesis showed a synergetic effect on increasing astaxanthin production. Finally, astaxanthin production was enhanced by 2.1-fold compared with the parental strain without a reduction of cell growth.ConclusionsWe developed a system to strongly overexpress multiple genes in X. dendrorhous. Using this system, the synthetic pathway of mevalonate, a common substrate for isoprenoid biosynthesis, was enhanced, causing an increase in astaxanthin production. Combining this multiple gene overexpression system with a platform strain that overproduces mevalonate has the potential to improve industrial production of various isoprenoids in X. dendrorhous.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-014-0175-3) contains supplementary material, which is available to authorized users.
Highlights
Red yeast, Xanthophyllomyces dendrorhous (Phaffia rhodozyma) is the only yeast known to produce astaxanthin, an anti-oxidant isoprenoid that is widely used in the aquaculture, food, pharmaceutical and cosmetic industries
It has already been reported that overexpressing hmgR, which is one of genes involved in the mevalonate synthetic pathway, under its original promoter was critical to enhance the astaxanthin content in X. dendrorhous [10]
It has already been reported that overexpressing hmgR increased a carotenoid, lycopene, in a yeast Candida utilis mutant with an endogenous carotenoid synthetic pathway [11]
Summary
Xanthophyllomyces dendrorhous (Phaffia rhodozyma) is the only yeast known to produce astaxanthin, an anti-oxidant isoprenoid (carotenoid) that is widely used in the aquaculture, food, pharmaceutical and cosmetic industries. The common precursor for isoprenoid biosynthesis, has been shown to be critical to enhance the astaxanthin content in X. dendrorhous. Melillo, et al, showed the potential of the red yeast, Phaffia rhodozyma (sexual form, Xanthophyllomyces dendrorhous), as a platform microorganism for isoprenoids production because of the higher flux through its native terpene pathway compared with S. cerevisiae and E. coli [5]. This made cell growth slower because fatty acids and ergosterol are important structural components of the cell membrane This suggests that strengthening the mevalonate synthetic pathway by overexpressing genes encoding enzymes involved in the mevalonate synthetic pathway is a promising approach to enhance biosynthesis of astaxanthin or any other isoprenoids without additional compounds and effects on cell growth in X. dendrorhous. It has already been reported that overexpressing hmgR, which is one of genes involved in the mevalonate synthetic pathway, under its original promoter was critical to enhance the astaxanthin content in X. dendrorhous [10]
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