Triacylglycerol accumulation and profiling in the model diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum (Baccilariophyceae) during starvation

Although substantial economic barriers exist, marine diatoms such as Thalassiosira pseudonana and Phaeodactylum tricornutum hold promise as feedstock for biodiesel because of their ability to manufacture and store triacylglycerols (TAGs). The recent sequencing of these two marine diatom genomes by the United States Department of Energy Joint Genome Institute and the development of improved systems for genetic manipulation should allow a more systematic approach to understanding and maximizing TAG production. However, in order to best utilize these genomes and genetic tools, we must first gain a deeper understanding of the nutrient-mediated regulation of TAG anabolism. By determining both the yield and molecular species distribution of TAGs we will, in the future, be able to fully characterize the effects of genetic manipulation. Here, we lay the groundwork for understanding TAG production in T. pseudonana and P. tricornutum, as a function of nitrate and silicate depletion. Diatoms were starved of either nitrate or silicate, and TAGs were extracted with hexane from lyophilized samples taken at various time intervals following starvation. The timing of TAG production and the relative abundance of TAGs were estimated by fluorescence spectroscopy using Nile red and the total yield per biomass determined by gravimetric assay. TAGs were analyzed using thin layer chromatography, gas chromatography-mass spectrometry, and electrospray ionization mass spectrometry to identify the major TAG species produced during the growth curve. Under our conditions, the TAG yield from T. pseudonana is about 14-18% of total dry weight. The TAG yield from P. tricornutum is about 14% of total dry weight. Silicate-starved T. pseudonana accumulated an average of 24% more TAGs than those starved for nitrate; however, the chemotypes of the TAGs produced were generally similar regardless of the starvation condition employed.