The heterotrophic culture of Chlorella protothecoides for the production of lipids

In this age of concern about dwindling supplies of fossil fuels, research into alternative and especially renewable fuels is growing. Microalgae are seen to have potential as a source of biodiesel fuels via the lipids that they can produce. In this project, Chlorella protothecoides, a microalga which is claimed able to accumulate lipids to between 60 and 75%, was chosen for study of the heterotrophic production of lipids. The objectives of the project were to discover via examination of a sequence of fermentation variables, a set of conditions for good lipid yield, to elucidate the relationship between cell growth and lipid production, and to obtain quantitative data to characterize lipid production by Chlorella protothecoides UTEX250. Specific Growth Rate and Specific Rate of Lipid Production data indicate that lipid production by Chlorella protothecoides has the pattern of a primary metabolite when cultured at 25 degrees C. However, when incubated at 35 degrees C, the data suggests that lipids are a secondary metabolite. In shake flask culture, when an inoculum size of 20%, incubation temperature of 35 degreesC, shaking speed of 200 r.p.m., initial glucose concentration of 1.5%, a C:N ratio of 150 in the medium, and the culture pH is uncontrolled, a lipid yield of 44.8% of dry cell weight can be obtained. The lipids were produced with Yx/s at 3.23 and Yp/s at 0.066. When translated to a 4 L bioreactor culture, the lipid yield was similar at 46.1%. These results are at the lower end of a range of yields obtained in other heterotrophic studies with Chlorella protothecoides (46 -58%).