Cnidarian-Dinoflagellate Symbiosis Lipidomics Figure 6. The mass spectrum profile of the fatty acid, DHA (C22:6, n–3) within (A) Acropora millepora and (B) within a clade B dinoflagellate culture removed from the DI13C ASW treatments at 48 hr. (R.A.% = Relative Amount). doi:10.1371/journal.pone.0046801.g006 associated with regulation of cnidarian-dinoflagellate symbiosis [42]. The linear incorporation profile of palmitic acid (C16:0) (Figure 2B) was reciprocated in the conversion of a proportion into palmiteolic acid (C16:1, n–7) (Figure 2C). C16:0 is one of the most abundant FAs, a precursor to lipogenesis and in combination with C16:1 represent two of the main components of total lipids in the cnidarian-dinoflagellate consortium [9,14,40,43]. The consis- tent linear incorporation profile into C16:0 correlated with the continuous synthesis and turnover of a large quantity of FA for other products, as shown with a consistent increase in 13C as 12C supplies and subsequent incorporation were reduced over time. The C16:1 profile aligns with the C16:0 explanation for synthesis as this is a direct downstream derivative of C16:0. However, the function within the symbiosis remains unknown. In tracking lipogenesis pathways the saturated FA synthesized from C16:0 is stearic acid (C18:0), displayed a profile indicative of an intermediate undergoing rapid turnover into downstream oleic acid (C18:1) (Figure 2D and 3A). The subsequent high incorpora- tion within linoleic acid (C18:2) and linolenic acid (C18:3) from symbiotic anemones and CEDP followed the n–3 lipogenesis pathway, which is found within marine algae (Figure 3B and C). The C18:2, n–6 to C18:3 conversion is a potential diversion point for pathways of FA lipogenesis. The incorporation into either a- linolenic C18:3, n–3 or c-linolenic C18:3, n–6 from C18:2, n–6, was not examined, although both isomers were detected. However, by tracking downstream incorporation to either arachidonic acid (C20:4, n–6) or stearidonic acid (C18:4, n–3), the active pathway(s) for further incorporation can be identified. In keeping with this assumption, incorporation was detected within C18:4, I–3 (Figure 3D) and dihomo-c-linoleic acid (C20:3, n–6), indicating both further n–3 and n–6 activity in both the symbiotic anemones and CEDP (Figure 4A). The evidence of a division of DI13C resource between n–3 and n–6 pathways during long-chain FA synthesis, was only apparent within the dinoflagellate, which was reciprocated within the CEDP samples up until and including PLOS ONE | www.plosone.org 10 October 2012 | Volume 7 | Issue 10 | e46801