Microbial lipid production

Abstract

For the production of lipids by microbial means as an alternative or unique lipid source other than the conventional plant and animal sources, fundamental studies on such cellular physiology as growth, lipid production and biochemistry of lipid accumulation in oleaginous yeast have been undertaken. Rhodotorula gracilis (syn. Rh. glutinis) NRRL Y-1091, a red oleaginous yeast, has been grown under favorable and less favorablelipogenic conditions using batch and continuous culture systems. At first, to select most suitable carbon and nitrogen sources for the efficient lipid production, the yeast cells were grown on various carbon and nitrogen sources. Among the sources examined, glucose and ammonium sulfate were found to be most suitable. Both good growth and lipid production have also been observed when yeast cells are grown on cellulase hydrolyzate of alkali-treated rice straw. The quantitative physiology of the organism has been studied by use of a continuous culture system. Specific uptake rates of the key nutrients have been measured at various dilution rates, i.e., various specific growth rates, and from these results the cellular growth, yield coefficients and maintenance coefficients for each nutrient are obtained. From the fermentation data, the volumetric lipid productivity and specific lipid production rate also have been estimated. The lipids obtained from batch and continuous cultures are characterized in detail. The proportions of lipid classes in intracellular lipids have been changed as dilution rate altered. The amounts of components in each lipid class were also varied depending upon the cultural conditions. The effects of cultural conditions on fatty acid composition and degree of unsaturation have been observed. From the data of nutrient consumption, growth yield coefficient and lipid analysis, the conversion efficiency of glucose to storage lipid has been estimated. The catabolic pattern of glucose in oleaginous yeast is known to be different ...