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PLoS One. 2018 Sep 27;13(9):e0204505. doi: 10.1371/journal.pone.0204505. eCollection 2018.

Induction of oil accumulation by heat stress is metabolically distinct from N stress in the green microalgae Coccomyxa subellipsoidea C169.

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Department of Biochemistry, Beadle Center, University of Nebraska-Lincoln, University of Nebraska-Lincoln, Lincoln, NE, United States of America.
Department of Chemical and Biomolecular Engineering, Othmer Hall, University of Nebraska-Lincoln, Lincoln, NE, United States of America.


Algae are often promoted as feedstock organisms to produce a sustainable petroleum fossil fuel alternative. However, to induce lipid accumulation most often requires a severe stress that is difficult to induce in large batch cultures. The objective of this study is to analyze and mathematically model heat stress on growth, chlorophyll content, triacylglyceride, and starch synthesis in algae. We initially screened 30 algal species for the most pronounced induction of lipid droplets from heat stress using confocal microscopy and mass spectroscopy techniques. One species, Coccomyxa subellipsoidea C169, was selected and subjected to further biochemical analyses using a jacketed bioreactor amended with 1% CO2 at 25°C, 30°C, 32°C, 33°C, 34°C, 35°C, and 36°C. Lipid and starch accumulation was less extreme than N stress. Growth was reduced above 25°C, but heat stress induced lipid droplet synthesis was negatively correlated with growth only past a demonstrated threshold temperature above 32°C. The optimal temperature for lipid accumulation was 35°C, which led to 6% of dry weight triglyceride content and a 72% reduction from optimal growth after 5 days. Fatty acid influx rates into triglycerides and 15N labeling of amino acids and proteins indicate that heat stress is mechanistically distinct from N stress. Thus, this study lends support to a novel hypothesis that lipid droplet triglycerides result from a redistribution of carbon flux as fatty acids to neutral storage lipids over membrane or other lipids.

Conflict of interest statement

Affiliations with Vestal W2O LLC and The Vajra Instruments Inc. do not alter our adherence to PLOS ONE policies on sharing data and materials.

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