New Biosynthetic Pathways to Highly Branched Isoprenoid (HBI) Alkenes in Diatoms

Guillaume Massé1,2, W. Guy Allard1, Simon T. Belt1, Jean-Michel Robert2 and Steven J. Rowland1


Petroleum and Environmental Geochemistry Group, Department of Environmental Sciences and Plymouth Environmental Research Centre (PERC), University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, U.K.
2 ISOMer, UPRES-EA 2663, Faculté des Sciences, Université de Nantes, 2 rue de la Houssinière, 44322 Nantes Cedex 3, France

Presented at: 23rd International Symposium on the Chemistry of Natural Products, Florence, Italy, 28th July-2nd August 2002.

Download: Poster as an A4 pdf file.

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.

Top of Page Recent PEGG Posters PEGG Home Page