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.

Small angle neutron scattering (SANS) was used to study the structure of Avicel (FD100) microcrystalline cellulose during enzymatic digestion. Digestions were performed in either of two modes: a static, quiescent mode or a dynamic mode using a stirred suspension recycled through a flow cell. The scattering pattern for as-received Avicel in D(2)O buffer is comprised of a low Q power law region resulting from the surface fractal character of the microcrystalline fibers and a high Q roll-off due to scattering from water-filled nanopores with radii approximately 20 A. For digestions in the dynamic mode the high Q roll-off decreased in magnitude within approximately 1 h after addition of enzymes, whereas in the static digestions no change was observed in the high Q roll-off, even after 60 h. These results indicate that only with significant agitation does enzyme digestion affect the structure of the nanopores.

Algal biofuels are a growing interest worldwide due to their potential in terms of sustainable greenhouse gas displacement and energy production. This article describes a comparative survey of biodiesel production and conversion yields of biodiesel via alkaline transesterification of acylglycerols extracted from the microalgae Thalassiosira pseudonana and Phaeodactylum tricornutum, grown under silicate or nitrate limitation, and that of model vegetable oils: soybean, and rapeseed oil. Acylglycerols were extracted with n-hexane and the total yield per biomass was determined by gravimetric assay. Under our conditions, the total acylglycerol yield from the microalgae studied was 13-18% of total dry weight. The biodiesel samples were analyzed using gas chromatography-flame ionization detector to determine quantitative information of residual glycerol, mono-, di-, and tri-acylglycerol concentrations in the biodiesel. All of the algal-based biodiesel demonstrated less mono-, di-, and tri-acylglycerol concentrations than the vegetable-based biodiesel under identical transesterification conditions. The fatty acid compositions of all the feedstock oils and their resultant biodiesel were also analyzed and reported. Based on the fatty acid methyl ester compositions of our samples we qualitatively assessed the suitability of the algal-derived biodiesel in terms of cetane number (CN), cold-flow properties, and oxidative stability.