Dynamics of Lipid Biosynthesis and Redistribution in the Marine Diatom Phaeodactylum tricornutum Under Nitrate Deprivation Elizabeth H. Burrows & Nicholas B. Bennette & Damian Carrieri & Joseph L. Dixon & Anita Brinker & Miguel Frada & Steven N. Baldassano & Paul G. Falkowski & G. Charles Dismukes Published online: 4 May 2012 # Springer Science+Business Media, LLC 2012 Abstract One approach to achieve continuous overproduc- tion of lipids in microalgal “cell factories” relies upon de- pletion or removal of nutrients that act as competing electron sinks (e.g., nitrate and sulfate). However, this strat- egy can only be effective for bioenergy applications if lipid is synthesized primarily de novo (from CO 2 fixation) rather than from the breakdown and interconversion of essential cellular components. In the marine diatom, Phaeodactylum tricornutum, it was determined, using 13 C-bicarbonate, that cell growth in nitrate (NO 3 - )-deprived cultures resulted predominantly in de novo lipid synthesis (60 % over 3 days), and this new lipid consisted primarily of triacylglycerides (TAGs). Nearly complete preservation of 12 C occurred in all previously existing TAGs in NO 3 - -deprived cultures and thus, further TAG accumulation would not be expected from inhibition of TAG lipolysis. In contrast, both high turnover and depletion of membrane lipids, phosphatidylcholines (PCs), were observed in NO 3 - -deprived cultures (both the headgroups and fatty acid chains), while less turnover was observed in NO 3 - replete cultures. Liquid chromatography- tandem mass spectrometry mass spectra and 13 C labeling patterns of PC headgroups provided insight into lipid syn- thesis in marine diatoms, including suggestion of an internal pool of glycine betaine that feeds choline synthesis. It was also observed that 16C fatty acid chains incorporated into TAGs and PCs contained an average of 14 13 C carbons, indicating substantial incorporation of 13 C-bicarbonate into fatty acid chains under both nutrient states. Keywords Algae . Biodiesel . Nitrate . Nutrients . Fatty acid metabolism . De novo lipid biosynthesis . Phaeodactylum tricornutum Introduction Photosynthesis stores solar energy as chemical bond energy in the form of carbohydrates, lipids, and other cellular ma- terial, and photosynthetically derived lipids can be extracted or secreted and readily saponified and transesterified to form biodiesel [1]. Although lipid-rich plants, such as soybean, jatropha, and oil palm, have received much attention, some natural strains of aquatic microalgae have 6- to 12-fold higher energy yield per unit area per year than terrestrial crops [2] and the theoretical maximum per unit area per year is almost 60 times reported yields for the most productive terrestrial crops [3]. Electronic supplementary material The online version of this article (doi:10.1007/s12155-012-9201-7) contains supplementary material, which is available to authorized users. E. H. Burrows : N. B. Bennette : G. C. Dismukes (*) Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, USA e-mail: dismukes@rci.rutgers.edu D. Carrieri : S. N. Baldassano Department of Chemistry, Princeton University, Piscataway, NJ, USA J. L. Dixon : A. Brinker Department of Nutritional Sciences, Rutgers University, Piscataway, NJ, USA J. L. Dixon : A. Brinker : P. G. Falkowski Rutgers Center for Lipid Research, Rutgers University, Piscataway, NJ, USA M. Frada : P. G. Falkowski Environmental Biophysics and Molecular Ecology Program, Rutgers University, Piscataway, NJ, USA Bioenerg. Res. (2012) 5:876–885 DOI 10.1007/s12155-012-9201-7