High contents of eicosapentaenoic acid and docosahexaenoic acid in the mixotrophic dinoflagellate Paragymnodinium shiwhaense and identification of putative omega-3 biosynthetic genes

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are critical components and beneficial to human health. Some marine protists are known to have high contents of these omega-3 fatty acids, and thus the contents of newly described protists should be explored for their potential utility. The newly described dinoflagellate Paragymnodinium shiwhaense is known to grow mixotrophically, but not autotrophically. To examine the fatty acids of P. shiwhaense, the composition of the fatty acids and contents of EPA and DHA of P. shiwhaense fed on each of three optimal prey species, the dinoflagellate Amphidinium carterae, the raphidophyte Heterosigma akashiwo, and the cryptophyte Teleaulax sp., were investigated. Furthermore, the genes involved in EPA and DHA biosynthetic pathways in P. shiwhaense were identified by analyzing the whole transcriptomic sequencing data of this species. P. shiwhaense had high contents of EPA (19% of total fatty acids) and DHA (36%) when fed on A. carterae. However, the contents of EPA in P. shiwhaense fed on H. akashiwo, and Teleaulax sp. were only 7% and 3%, respectively. In contrast, the contents of DHA in P. shiwhaense fed on H. akashiwo, and Teleaulex sp. were 43% and 31%, respectively. Thus, the DHA contents of P. shiwhaense may not be largely affected by prey species, but that the EPA contents are affected. The EPA produced by P. shiwhaense may be converted to DHA using Δ4-desaturase and Δ5-fatty acyl elongase genes, which were identified in this study. Furthermore, Δ5 and Δ6-desaturase and Δ6-fatty acyl elongase genes were also identified. To the best of our knowledge, this is the first time that these genes have been reported in this taxonomic group of dinoflagellates.