From 1992 to 1995, Dr. Jane Schneider worked at NREL with Dr. Roessler on a project funded by the United States-Israel Binational Agricultural Research and Development Fund. The research was performed in collaboration with Dr. Assaf Sukenik and other scientists at the Israel Oceanographic and Limnological Institute in Haifa. The goal of the research was to understand the biochemistry of lipid synthesis in the eustigmatophyte Nannochloropsis sp., particularly with respect to fatty acid desaturation pathways. There has been a significant amount of research on lipid synthesis pathways in higher plants, and the pathways hve been assumed to be similar in lipogenic algae. However, unlike plants, nutrient deprivation produces major effects on the quantity and quality of lipids in algae; so there are likely to be significant differences in the biochemical pathways. In addition, like many algae, Nannochloropsis contains a high proportion of long fatty acids (i. e., C-20, C-22) with a high degree of unsaturation (20:5). These very long chain-polyunsaturated fatty acids (VLC-PUFAs) are important in aquaculture applications as they improve the nutritional quality of feed for fish and shellfish, and have nutritional and pharmaceutical applications for humans. Understanding the details of the biochemistry of lipid accumulation in microalgae could help researchers develop strategies for genetic manipulation of lipid synthesis pathways to affect not only the quantity but also the quality (chain length, degree of desaturation) of lipids produced for optimal biodiesel performance.

In one set of experiments, pulse-chase radiolabeling was used to study de novo synthesis of lipids in Nannochloropsis. Exponentially growing cells under low light were fed 14C-bicarbonate or acetate for 1 hour. The cells were then washed and allowed to grow in unlabeled medium. At various time points, cells were removed and lipids extracted. The substrates resulted in a different distribution of labeled carbon in the lipids and fatty acids. The work demonstrated the probable existence of two pools of malonyl-CoA used as substrates for fatty acid synthesis, and resulted in a new model for the sites of desaturation of fatty acids and the identification of a new acyltransferase activity in this organism. In another set of experiments, Nannochloropsis cells were mutagenized using UV light and screened for unusual fatty acid profiles using gas chromatography. This work resulted in the isolation of a mutant deficient in 20:5 fatty acids, probably due to a mutation affecting a desaturase enzyme that utilizes 20:4 fatty acids as substrate.

These experiments will not be described in detail here, primarily because the funding for this research did not come from DOE. In addition, it would require a lengthy discussion of the details of fatty acid synthesis and processing for the reader to understand the relevance of the findings. Readers interested in the details of this research are referred to the three publications that resulted from this research (Schneider and Roessler 1994; Schneider et al. 1995; Schneider and Roessler 1995).