Fife Yeast Biosynthesis Of Astaxanthin

The wild strain of Phaffla rhodozyma is low in astaxanthin productivity. The most important task is to screen high astaxanthin-producing mutants for potential commercial application. After chemical mutation treatment by NTG and careful design of selective medium, mutants with high astaxanthin productivity were obtained, in which, the astaxanthin yield was three times higher than that in wild strain. Also the cultivation temperature of wild strain is low (? 1 0C), to screen a strain with higher cultivation temperature is favorable. Three mutants were obtained from the NTG mutation treatment, which could grow on YM medium at 280C. But the mutants can only produce carotenoids without astaxanthin accumulation. Cultivation conditions and nutrition composition can greatly affect Phaffia rhodozyma growth and astaxanthin accumulation. Experimental results showed that Phaffia rhodozyma is able to metabolize various kinds of carbon sources, of which, cellubiose, glucose, sucrose, and maltose are good ones for cell growth and astaxanthin biosynthesis. The optimal carbon and nitrogen sources were: Glucose concentration 3%, (NH4)2S04 0.5%, and the initial pH value should be adjusted to pH 4.5-5.5. The inoculation size of 5-10% was suitable for high astaxanthin productivity. Because of high oxygen requirement in astaxanthin biosynthesis, enhancement of oxygen supply is very important for cell growth and astaxanthin accumulation. The results indicated that there exist a linear relationship between dissolved oxygen concentration and astaxanthin productivity. Addition of precursors of astaxanthin such as carrot and tomato juice into the media could improve the accumulation of astaxanthin in III Abstract Phaffia rhodozyma. Astaxanthin accumulation in Phaffia rhodozyma was associated with cell growth in Phafjia rhodozyma. Because of 揼lucose effects? high initial glucose concentration (eg. >4%) will inhibit cell growth and astaxanthin formation in batch culture. And continuous culture also gave out poor results. Fed-batch fermentation would be a good approach to increase cell density, therefore, astaxanthin productivity. In this work, various fed- batch fermentation modes were adopted, and cell growth as well as astaxanthin production were compared. With constant feeding, exponential feeding, pH-stat and p02-stat fed-batch fermentation modes, the highest DCW (31 .56g11) and astaxanthin formation(1 7.12mg/I) were observed in exponential- feeding culture. In both exponential fed-batch and p02-stat fed- batch modes, the Y~/5 were aboutt 3mgI(g glucose). When tomato juice and carotene were fed, astaxanthin yield was increased obviously, up to 15.21mg/I and 6.1 2mg/I respectively. Because of glucose effect, during Phaffia rhodozyma fermentation, partial glucose will be used for ethanol synthesis besides for cell growth and astaxanthin formation even in aerobic condition. After glucose is consumed, the yeast cells can metabolize ethanol for diauxic cell growth as well as product formation. A mathematical model was proposed to describe the above phenomena. The model parameters were simulated from experimental data and the calculated curves were in good agreement with the experimental data.