Towards the Industrial Production of Omega-3 Long Chain Polyunsaturated Fatty Acids from a Genetically Modified Diatom Phaeodactylum tricornutumReport as inadecuate

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The marine diatom Phaeodactylum tricornutum can accumulate up to 30% of the omega-3 long chain polyunsaturated fatty acid LC-PUFA eicosapentaenoic acid EPA and, as such, is considered a good source for the industrial production of EPA. However, P. tricornutum does not naturally accumulate significant levels of the more valuable omega-3 LC-PUFA docosahexaenoic acid DHA. Previously, we have engineered P. tricornutum to accumulate elevated levels of DHA and docosapentaenoic acid DPA by overexpressing heterologous genes encoding enzyme activities of the LC-PUFA biosynthetic pathway. Here, the transgenic strain Pt Elo5 has been investigated for the scalable production of EPA and DHA. Studies have been performed at the laboratory scale on the cultures growing in up to 1 L flasks a 3.5 L bubble column, a 550 L closed photobioreactor and a 1250 L raceway pond with artificial illumination. Detailed studies were carried out on the effect of different media, carbon sources and illumination on omega-3 LC-PUFAs production by transgenic strain Pt Elo5 and wild type P. tricornutum grown in 3.5 L bubble columns. The highest content of DHA 7.5% of total fatty acids, TFA in transgenic strain was achieved in cultures grown in seawater salts, Instant Ocean IO, supplemented with F-2 nutrients F2N under continuous light. After identifying the optimal conditions for omega-3 LC-PUFA accumulation in the small-scale experiments we compared EPA and DHA levels of the transgenic strain grown in a larger fence-style tubular photobioreactor and a raceway pond. We observed a significant production of DHA over EPA, generating an EPA-DPA-DHA profile of 8.7%-4.5%-12.3% of TFA in cells grown in a photobioreactor, equivalent to 6.4 μg-mg dry weight DHA in a mid-exponentially growing algal culture. Omega-3 LC-PUFAs production in a raceway pond at ambient temperature but supplemented with artificial illumination 110 μmol photons m-2s-1 on a 16:8h light:dark cycle, in natural seawater and F-2 nutrients was 24.8% EPA and 10.3% DHA. Transgenic strain grown in RP produced the highest levels of EPA 12.8% incorporated in neutral lipids. However, the highest partitioning of DHA in neutral lipids was observed in cultures grown in PBR 7.1%. Our results clearly demonstrate the potential for the development of the transgenic Pt Elo5 as a platform for the commercial production of EPA and DHA.

Author: Mary L. Hamilton, Joanna Warwick, Anya Terry, Michael J. Allen, Johnathan A. Napier, Olga Sayanova



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