Long chain polyunsaturated fatty acids (PUFAs), such as the omega-3 fatty acids eicosapentaeonic (EPA) and docosahexaenoic (DHA), are produced by a seemingly small fraction of marine microorganisms, which supply these essential lipids to the rest of the food web. While microalgae typically use FA desaturases to produce omega-3 PUFAs in the surface ocean, a pathway involving polyketide synthases, encoded by the pfa gene cluster, has been found in unicellular eukaryotes and a few bacterial isolates. However, the contribution of these taxa to the production of PUFAs in the global ocean remains unknown. To determine the global diversity, abundance, and activity of potential marine microbial PUFA producers, we have examined more than 35,000 microbial genomes from the Ocean Microbiomics database and the eukaryotic fraction of Tara Oceans. We detected 240 potential PUFA producers, some of them featuring a novel domain architecture of the pfa gene cluster. Known producers of omega-3 PUFAs (e.g., Shewanella, Colwellia, Vibrio) did not show high abundance or activity in marine metagenomes and metatranscriptomes. By contrast, we uncovered the presence of the pfa gene cluster in ecologically relevant lineages such as SAR324, which presented high cumulative abundance and activity in all ocean layers, especially at depth. Our results broaden the current knowledge on potential PUFA suppliers to the marine trophic web, including the mesopelagic and bathypelagic realm. For these microorganisms, PUFAs may have a key role in their adaptation to cold temperature or high-pressure conditions.

Primary Presenter: Raquel Liébana, AZTI (rliebana@azti.es)

Authors:

Raquel Liébana, AZTI  (rliebana@azti.es)

Anders Lanzén, AZTI  (alanzen@azti.es)

Francisco M. Cornejo-Castillo, ICM-CSIC  (fmcornejo@icm.csic.es)

Pablo Sánchez, ICM-CSIC  (pablosanchez@icm.csic.es)

Josep M. Gasol, ICM-CSIC  (pepgasol@icm.csic.es)

Silvia G. Acinas, ICM-CSIC  (sacinas@icm.csic.es)

Laura Alonso-Sáez, AZTI  (lalonso@azti.es)