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Abstract
BackgroundThe yeast Xanthophyllomyces dendrorhous is one of the most promising and economically attractive natural sources of astaxanthin. The biosynthesis of this valuable carotenoid is a complex process for which the regulatory mechanisms remain mostly unknown. Several studies have shown a strong correlation between the carbon source present in the medium and the amount of pigments synthesized. Carotenoid production is especially low when high glucose concentrations are used in the medium, while a significant increase is observed with non-fermentable carbon sources. However, the molecular basis of this phenomenon has not been established.ResultsIn this work, we showed that glucose caused transcriptional repression of the three genes involved in the synthesis of astaxanthin from geranylgeranyl pyrophosphate in X. dendrorhous, which correlates with a complete inhibition of pigment synthesis. Strikingly, this regulatory response was completely altered in mutant strains that are incapable of synthesizing astaxanthin. However, we found that addition of ethanol caused the induction of crtYB and crtS gene expression and promoted de novo synthesis of carotenoids. The induction of carotenogenesis was noticeable as early as 24 h after ethanol addition.ConclusionFor the first time, we demonstrated that carbon source-dependent regulation of astaxanthin biosynthesis in X. dendrorhous involves changes at the transcriptional level. Such regulatory mechanism provides an explanation for the strong and early inhibitory effect of glucose on the biosynthesis of this carotenoid.
Highlights
The yeast Xanthophyllomyces dendrorhous is one of the most promising and economically attractive natural sources of astaxanthin
Effect of glucose on the expression of carotenoid biosynthesis genes Several observations support the hypothesis that glucose has an inhibitory effect on carotenoid production in
To determine whether glucose affects the expression of the carotenogenic genes, X. dendrorhous cells were grown in YM liquid medium without glucose to prevent the production of ethanol, which can influence the phenomenon under investigation
Summary
The yeast Xanthophyllomyces dendrorhous is one of the most promising and economically attractive natural sources of astaxanthin The biosynthesis of this valuable carotenoid is a complex process for which the regulatory mechanisms remain mostly unknown. During the first phase of biosynthesis, the phytoene synthase activity of the bifunctional enzyme phytoene-b-carotene synthase (PBS, product of crtYB) catalyzes the condensation of two GGPP molecules to produce one molecule of phytoene, the first carotenoid of the pathway [5]. The b-carotene is oxidized at both ends in a process that requires cytochrome p450 astaxanthin synthase (product of crtS) [7,8] This reaction requires the accessory activity of a cytochrome p450 reductase enzyme as an electron donor [9]
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