Brief Summary

C₂₅ and C₃₀ highly branched isoprenoid (HBI) alkenes are unusual secondary metabolites that are derived from diatoms. Volkman and co-workers were the first to determine biological sources of these isoprenoids, namely the marine diatoms Haslea ostrearia (C₂₅) and Rhizosolenia setigera (C₃₀) (Volkman et al., 1994). Since this initial report, we have reported on a further species of diatom capable of biosynthesising the C₂₅ HBIs (viz. Pleurosigma intermedium) and elucidated the structures of numerous C₂₅ and C₃₀ HBIs (including the most widespread and abundant sedimentary isomers) following isolation from large scale diatom cultures and analysis by NMR spectroscopy (Belt et al., 2000ab ; Belt et al., 2001). Some representative structures of C₂₅ (haslenes) and C₃₀ (rhizenes) HBIs are shown in Fig. 1.

Whilst investigations into the biosynthesis of isoprenoids have seen a dramatic resurgence over the past few years, following the discovery of the so-called non-mevalonate pathway (Schwender et al., 1996 ; Rohmer, 1999), only one study of isoprenoid biosynthesis in diatoms has been made (Cvejic and Rohmer, 2000).

Here, we describe an investigation into the biosynthesis of phytol (C₂₀), and both C₂₅ and C₃₀ HBI alkenes by two different diatom species: Rhizosolenia setigera, a large ubiquitous planktonic diatom and Haslea ostrearia, a benthic pennate diatom (Fig. 2) using a combined approach integrating pathway specific blocking experiments and stable isotope incorporation (NMR and MS analysis). Our observations provide evidence for the co-occurrence of both mevalonate (MVA) and non-mevalonate (MEP) routes and reveal a dependence of the utilised pathways on the species under investigation.

Download the complete poster as an A4 pdf file.