(506a) Effect of C/N Ratio on Microbial Lipid Production with the Oleaginous Yeast Lipomyces Starkeyi

Neutral lipids have been used as raw materials for the production of biodiesel. Since agricultural and plant-derived neutral lipids are often utilized in food preparations, alternative sources of lipids are being investigated. A number of microorganisms possess the ability to produce significant fractions of their dry weight as neutral lipids. The oleaginous yeast, Lipomyces starkeyi, is a promising candidate for industrial production of neutral lipids which will ultimately be converted into biofuels. The yeast grows rapidly on various carbon sources and can produce lipids upto 75% of its dry weight. Lipid accumulation most commonly occurs when the nutrient supply is exhausted in the presence of excess carbon at the stationary phase. Under nutrient limiting conditions, yeast cells accumulate lipids as a means of storage when energy sources are abundantly available and when the cellular mechanisms for the microbial synthesis are active. In this research work, experiments are conducted by varying the C:N ratio in the growth medium, and its effect on cell growth and the accumulation of lipids.  The carbon source utilized in this work is laboratory grade sweet potato starch as well as starch from raw sweet potato.  All the experiments were conducted in the shake flasks as well as in the fermenters with controlled pH, and temperature conditions.  Different feeding strategies will also be studied and discussed with this presentation. Cell mass, starch content and lipid content were analyzed periodically.  The cell mass was recorded by weighing the sample before and after drying.  Lipid content was measured by Nile red florescence.  The supernatant from centrifugation or filtrate was used to measure starch concentration by iodine method.