Algal-derived biodiesel is of particular interest because of several factors including: the potential for a near-carbon-neutral life cycle, the prospective ability for algae to capture carbon dioxide generated from coal, and algae's high per acre yield potential. Our group and others have shown that in nitrogen limitation, and for a single species of Chlorella, a rise in culture medium pH yields triacylglycerol (TAG) accumulation. To solidify and expand on these triggers, the influence and interaction of pH and nitrogen concentration on lipid production was further investigated on Chlorophyceae Scenedesmus sp. and Coelastrella sp. Growth was monitored optically and TAG accumulation was monitored by Nile red fluorescence and confirmed by gas chromatography. Both organisms grew in all treatments and TAG accumulation was observed by two distinct conditions: high pH and nitrogen limitation. The Scenedesmus sp. was shown to grow and produce lipids to a larger degree in alkaliphilic conditions (pH >9) and was used to further investigate the interplay between TAG accumulation from high pH and/or nitrate depletion. Results given here indicate that TAG accumulation per cell, monitored by Nile red fluorescence, correlates with pH at the time of nitrate depletion.
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Financial disclosure/Acknowledgments The authors would like to thank Dr. Brett Barney and the Seefeldt lab group (Utah State University) for assistance with the gas chromatographic analyses and for technical support from the Montana State University Algal Biofuels Group, especially, Dr. Matthew Fields and Grant Justin for molecular fingerprinting work done on CHLOR-1 and PC-3. Also of special note is the 18S rRNA gene sequence interrogations done by Seth D’Imperio and Rich Macur, along with instrumental support from the Montana State University Center for Biofilm Engineering. Funding was provided by the Air Force Office of Scientific Research (AFOSR grant FA9550-09-1-0243), US Department of Energy (Office of Biomass Production grant DE-FG36-08GO18161), and support for RG was provided by NSF IGERT Program in Geobiological Systems (DGE 0654336) at Montana State University.
- Fatty acid methyl ester (FAME)
- Nile red fluorescence
- Nile-red-specific fluorescence
- Triacylglycerol (TAG)