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INHIBITION OF ASTAXANTHIN SYNTHESIS ..

the astaxanthin biosynthesis of Xanthophyllomyces dendrorhous

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Astaxanthin synthesis by Xanthophyllomyces ..

Classical mutagenesis is typically performed as the initial strategy for overproduction of astaxanthin in P. rhodozyma. The mutant MK19 was selected as an astaxanthin-overproducing host strain. Astaxanthin yield can be further enhanced by genetic modification of the carotenoid synthesis pathway. We were interested by a pink/purple-colored unknown carotenoid whose level was ~15% higher in MK19 than in wild-type strain. To evaluate the potential of the unknown compound as a substrate for further production of astaxanthin through up-regulation of astaxanthin synthase (CrtS) gene, an episomal vector to achieve functional CrtS overexpression in homologous host MK19 was used and examined the effect on astaxanthin synthesis.

Inhibition of astaxanthin synthesis in the green alga, Haematococcus pluvialis

Carotenoid composition of cultured CSR19 during bioreactor fermentation was evaluated in detail. HPLC profiles of pigments at 24, 40, and 60 h are shown in Figure a, b, c. The 24-h sample, besides major peaks 1 (astaxanthin) and 2 (HDCO), has minor peaks corresponding to intermediate products such as keto carotenoids and β-carotene. In contrast, only peaks 1 and 2 are detectable in the 40-h and 60-h samples. The carotenoid profile changed and sampling time details were shown in Figure d. The proportion of HDCO relative to total carotenoids increased from 17 to 19% until the stationary phase began at 40 h; thereafter the HDCO proportion declined by 6% while the astaxanthin proportion increased by 6%. Little change in total carotenoid and β-carotene content was observed during the entire conversion process. It is therefore reasonable to assume a relationship between the synthesis levels of HDCO and astaxanthin; the reduced proportion of the former was associated with the increased proportion of the latter (and high CrtS level) during the period of rapid astaxanthin accumulation (40–60 h). At the end of culture, the proportion of astaxanthin was 84% (18% higher than in MK19) and that of HDCO was 13.4%. The only other components were trace carotenoids.

Metabolism of carotene and astaxanthin synthesis

The crtS gene in P. rhodozyma was originally reported as encoding a bifunctional hydroxylase/ketolase enzyme responsible for conversion of β-carotene to astaxanthin [, ]. Subsequent complementation experiments on P. rhodozyma mutants, and expression analysis in Mucor circinelloides and S. cerevisiae, showed that CrtS has only hydroxylase activity []. Based on the results of the present study, we propose that CrtS has bifunctional enzymatic activities in both the bicyclic and monocyclic carotenoid biosynthesis pathways. As indicated by the dashed line at the bottom of Figure , carotenoid substrates may be transformed to HDCO as well as astaxanthin during the pigment-accumulating period. HDCO may be converted to astaxanthin at later stages of cell growth, through enhanced CrtS activity.

The large observed increase in astaxanthin suggested that it was not the inhibitor of this multi-enzyme reaction sequence. Our kinetic studies of mRNA expression patterns of structural carotenogenic genes and their relationship with carotenoid biosynthesis showed significant differences (p crtE and crtS) during the cell growth period (48 h). When entering the stationary phase (72 h), transcription levels in CSR19 compared with CS19 were 3 times higher for crtE, crtYB, and crtI, and 2 times higher for crtS (p crtS expression in CSR19 relative to CS19, in contrast to the other three carotenogenic genes which remained more highly expressed in CSR19. In the two transformants, differential expression patterns of the four genes were correlated with differential carotenoid formation patterns.

Astaxanthin chemical synthesis | …

Proportions of various pigment compounds in the three strains are shown in Table . Relative to MK19, CSR19 had a 7% higher proportion of astaxanthin, 6% lower proportion of β-carotene, and similar proportion of the unknown carotenoid. In contrast, CS19 had similar astaxanthin, 5% lower β-carotene, and 4% higher proportion of the unknown carotenoid. These findings indicated that redundant substrates for xanthophyll synthesis (e.g., β-carotene and keto derivatives) may be further transformed to both astaxanthin and the unknown carotenoid through increased CrtS (astaxanthin synthase) activity.

CSR19 and CS19 differ in the Rbs sequence in the upper end of expressed target gene crtS. The comparative study of cell growth and astaxanthin synthesis suggested that Rbs of crtS (harbored by pGBKT7-crtSr) has higher affinity with ribosomes, which results in more efficient synthesis of CrtS. Changes in metabolic flux direction were observed among carotenoid biosynthesis pathways, those indicated adaptation to differences in CrtS activity between CSR19 and CS19.

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Astaxanthin: structural and functional aspects - SciELO

The effects of broth amount (6 vs. 10% filling amount) on growth and carotenogenesis of the three strains were also studied. Because of their higher carotenoid synthesis, CSR19 and CS19 were less sensitive to oxygen content in medium; biomass accumulation and carotenoid synthesis did not show difference markedly for 6 vs. 10% filling amount. Limitation of oxygen supply is often a problem in industrial fermentation; therefore, the lack of sensitivity to this parameter is an advantage for astaxanthin production.

The Antioxidant Astaxanthin: An Interview with Rudi …

Cell growth and astaxanthin yield for the three strains are summarized in Figure . Both these parameters were promoted in CSR19 and CS19, thereby enhancing oxidative stress tolerance. Carotenoids, being secondary metabolites, are not essential for cell survival, but do promote biomass accumulation under oxidative conditions. Cell dry weight after 120 h was enhanced by 36.5 and 12.2% for CSR19 and CS19 respectively, compared with MK19 (Figure a). CrtS overexpression resulted in excessive astaxanthin production. Maximal astaxanthin yield was 25.3 mg/L for CSR19 and 21.2 mg/L for CS19, that 33.5 and 11.8% higher than for MK19, respectively (Figure b). These results demonstrated the capacity of P. rhodozyma for increased carotenoid synthesis, and its potential as a “cell factory” for commercial-scale production of various carotenoids.

Spirulina and Astaxanthin | Uses and Benefits | Nutrex …

CSR19, CS19, and MK19 were grown in flasks to evaluate the effect of CrtS overexpression. Aliquots were collected at 24, 48, 72, 96, and 120 h for determination of biomass production and amounts of synthesized astaxanthin. Experiments were performed in triplicate or quadruplicate.

Product Ingredients - Skin Biology

Astaxanthin is the most developed xanthophyll, and its antioxidant activity is higher than that of other carotenoids []. The goal of most P. rhodozyma studies is to increase production of total carotenoid pigments, particularly astaxanthin. Genetic engineering of the carotenoid biosynthesis (carotenogenic) pathway is a powerful tool for enhancing astaxanthin production [, , ].

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