The Study On The Key Techniques For The Production Of Astaxanthin By Fermentation In Xanthophyllomyces Dendrorhous

The red yeast Xanthophyllomyces dendrorhous (formerly known as Phaffiarhodozyma) is one of the most promising microorganisms for biotechnological productionof dietary astaxanthin. In the process of X. dendrorhous fermentation，large amount ofoxygen was consumed to maintain cell metabolic level. Vitreosilla Hemoglobin (VHb) is akind of oxygen-binding protein of prokaryotic origin. The aim of this study is to expressvgb gene in X. dendrorhous, and to improve cell growth and astaxanthin production byenhancing the oxygen usage ability of cell. In this study, we also reported that theapplication of lactic acid and ethyl lactate to astaxanthin extraction from X. dendrorhous,and efficacy of antioxidants addition in protecting against oxidative degradation during theextraction process.(1) This report gives an insight into the specific changes in the transcription of fourkey carotenogenic genes (encoding geranylgeranyl diphosphate synthase (crtE), phytoenedesaturase (crtI), phytoene synthase lycopene cyclase (crtYB), and astaxanthin synthase(ast), respectively) in X. dendrorhous cultures, with regard to various dissolved oxygen(DO) contents and carbon sources. Our results suggested that a correlation betweenbiomass, astaxanthin production, and the transcripts of carotenogenic genes was evident inthe cells cultured with various substrates and DO concentration.(2) The recombinant vector pBC-Pcpc-vgb-Tnos contain vgb gene which waspromoted by the promoter of cpc-1was constructed, and the Recombinant vector wasintegrated in the chromosome of X. dendrorhous by electroporation. We confirmedrecombinants by Hygromycin B selection and PCR, and screened out twoastaxanthin-overproducing strains from the recombinants. The biomass, astaxanthin yieldand astaxanthin content of engineering strains were increased by21%,37%and13%,respectively than the original strain. PCR analysis indicated vgb had been integrated in tothe chromosome of X. dendrorhous, and CO binding difference speetrum analysis ofrecombinant strain showed that active VHb protein has been expressed in X. dendrorhous.At the same time the recombinant strain was stable at the generation and yield, andsuitable for industrial application. (3) The optimum extraction conditions were as follows: the yeast cell wall wasdisrupted by lactic acid at65oC for1h and then extracted with ethyl lactate: ethanol (1:1,v/v) for0.5h. The results showed that lactic acid and ethyl lactate has an obviouspredominance for the extraction of food-grade astaxanthin, and TOC was proved to be ahigh efficient natural antioxidant in our tests.