Genes for de novo biosynthesis of omega-3 polyunsaturated fatty acids are widespread in animals

Marine ecosystems are responsible for virtually all production of omega-3 (omega 3) long-chain polyunsaturated fatty acids (PUFA), which are essential nutrients for vertebrates. Current consensus is that marine microbes account for this production, given their possession of key enzymes including methyl-end (or omega x) desaturases. cox desaturases have also been described in a small number of invertebrate animals, but their precise distribution has not been systematically explored. This study identifies 121 omega x desaturase sequences from 80 species within the Cnidaria, Rotifera, Mollusca, Annelida, and Arthropoda. Horizontal gene transfer has contributed to this hitherto unknown widespread distribution. Functional characterization of animal cox desaturases provides evidence that multiple invertebrates have the ability to produce omega 3 PUFA de novo and further biosynthesize omega 3 long-chain PUFA. This finding represents a fundamental revision in our understanding of omega 3 long-chain PUFA production in global food webs, by revealing that numerous widespread and abundant invertebrates have the endogenous capacity to make significant contributions beyond that coming from marine microbes.