Lipid-Derived Biofuels: Determination of Factors that Control Triglyceride Accumulation in Microalgae
Final rept. 1 Mar 2009-31 Oct 2012
MONTANA STATE UNIV BOZEMAN
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The generality of earlier work with a Chlorophyte was verified in four other Chlorophytes and three diatoms. Neutral lipid droplet accumulation was dependent on medium pH at stationary phase. It was not entirely dependent on medium N and responded positively to bicarbonate addition 25-50mM to the medium close to stationary phase. Bicarbonate inhibited cell replication in Chlorophytes but not in diatoms, indicating different Inorganic carbon acquisition systems. Effects of N and P limitation were cumulative. Transcriptomic analyses of Phaeodactylum tricornutum cultures when lipid accumulation was maximal showed that genes related to P or N acquisition were up-regulated, as were genes related to carbon uptake possible C-4 pathway. Expression of genes involved directly in lipid accumulation were unchanged, suggesting that control of lipid accumulation is not at the level of acetyl CoA carboxylase, but earlier in the pathway. Real time PCR supported these conclusions. Changes in expression of genes related to control of the cell cycle Cyclins were observed which may explain a general mechanism for lipid accumulation in microalgae.