Microalgae Synthesize Hydrocarbons from Long-Chain Fatty Acids via a Light-Dependent Pathway

Microalgae are considered a promising platform for the production of lipid-based biofuels. While oil accumulation pathways are intensively researched, the possible existence of a microalgal pathways converting fatty acids into alka(e)nes has received little attention. Here, we provide evidence that...

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Published in:Plant physiology (Bethesda) 2016-08, Vol.171 (4), p.2393-2405
Main Authors: Sorigué, Damien, Légeret, Bertrand, Cuiné, Stéphan, Morales, Pablo, Mirabella, Boris, Guédeney, Geneviève, Li-Beisson, Yonghua, Jetter, Reinhard, Peltier, Gilles, Beisson, Fred
Format: Article
Language:English
Subjects:
Alkanes - chemistry
Alkanes - metabolism
Alkenes - chemistry
Alkenes - metabolism
Biochemistry
BIOCHEMISTRY AND METABOLISM
Biochemistry, Molecular Biology
Biofuels
Biomass
Biosynthetic Pathways
Biotechnology
Botanics
Chlamydomonas reinhardtii - chemistry
Chlamydomonas reinhardtii - genetics
Chlamydomonas reinhardtii - metabolism
Chlamydomonas reinhardtii - radiation effects
Chlorella - metabolism
Chloroplasts - metabolism
Diatoms - metabolism
Fatty Acids - chemistry
Fatty Acids - metabolism
Hydrocarbons - chemistry
Hydrocarbons - metabolism
Life Sciences
Light
Microalgae
Oleic Acids - chemistry
Oleic Acids - metabolism
Stearic Acids - chemistry
Stearic Acids - metabolism
Vegetal Biology
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Summary:Microalgae are considered a promising platform for the production of lipid-based biofuels. While oil accumulation pathways are intensively researched, the possible existence of a microalgal pathways converting fatty acids into alka(e)nes has received little attention. Here, we provide evidence that such a pathway occurs in several microalgal species from the green and the red lineages. In Chlamydomonas reinhardtii (Chlorophyceae), a C17 alkene, n-heptadecene, was detected in the cell pellet and the headspace of liquid cultures. The Chlamydomonas alkene was identified as 7-heptadecene, an isomer likely formed by decarboxylation of cis-vaccenic acid. Accordingly, incubation of intact Chlamydomonas cells with per-deuterated D₃₁-16:0 (palmitic) acid yielded D₃₁-18:0 (stearic) acid, D₂₉-18:1 (oleic and cis-vaccenic) acids, and D₂₉-heptadecene. These findings showed that loss of the carboxyl group of a C₁₉ monounsaturated fatty acid lead to heptadecene formation. Amount of 7-heptadecene varied with growth phase and temperature and was strictly dependent on light but was not affected by an inhibitor of photosystem II. Cell fractionation showed that approximately 80% of the alkene is localized in the chloroplast. Heptadecane, pentadecane, as well as 7- and 8-heptadecene were detected in Chlorella variabilis NC64A (Trebouxiophyceae) and several Nannochloropsis species (Eustigmatophyceae). In contrast, Ostreococcus tauri (Mamiellophyceae) and the diatom Phaeodactylum tricornutum produced C₂₁ hexaene, without detectable C₁₅-C₁₉ hydrocarbons. Interestingly, no homologs of known hydrocarbon biosynthesis genes were found in the Nannochloropsis, Chlorella, or Chlamydomonas genomes. This work thus demonstrates that microalgae have the ability to convert C₁₆ and C₁₉ fatty acids into alka(e)nes by a new, light-dependent pathway.
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.16.00462