Cnidarian-Dinoflagellate Symbiosis Lipidomics Figure 7. Schematic representation of the lipogenesis pathways utilizing DI13C (HCO32) as a carbon source (dash arrow = potentially active and ? = links by evidence of incorporation, but not previously described) [2]. doi:10.1371/journal.pone.0046801.g007 incorporation into C20:4, n–6 at around 120 hr. Multiple pathway long-chain fatty acid lipogenesis have previously been proposed and shown in other algae [44,45,46], and appears to be also active within the dinoflagellate Symbiodinium sp. A proposed pathway interaction of these pathways as a result of this study is shown in Figure 7. Although n–6 FAs were detected continuously along the pathway up and including until adrenic acid (C22:4) within the dinoflagellates, the incorporation was only detected up to arachidonic acid (C20:4) which may link back across to the n–3 pathway and EPA (C20:5 n–3) and onwards downstream (Figure 7). There was no indication of direct utilization of DI13C in further n– 6 downstream products, including and beyond docosatetraenoic/ adrenic acid (C22:4, n–6), which would normally be attributed to host/animal only (Figure 4D). The remaining downstream FAs with incorporation were associated with the n–3 lipogenesis pathway (within the dinoflagellate) including eicosapentaenoic acid (EPA, C20:5) and docosapentaenoic/clupanodonic acid (DPA; C22:5), which ap- PLOS ONE | www.plosone.org 11 October 2012 | Volume 7 | Issue 10 | e46801