The Effects of Auxosporulation on the Distributions of C25 and C30 Highly Branched Isoprenoid (HBI) Alkenes in the Diatom Rhizosolenia setigera

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


Petroleum and Organic Geochemistry Group, Department of Environmental Sciences and Plymouth Environmental Research Centre (PERC), University of Plymouth, 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: 20th International Meeting on Organic Geochemistry (IMOG 2001), Nancy, France, 10th-14th September 2001.

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C25 and C30 highly branched isoprenoid (HBI) alkenes are unusual secondary metabolites that are derived from diatoms and commonly used as biological markers in sediments and other geochemical environments. 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). 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 isomers) following isolation from large scale diatom cultures and analysis by NMR spectroscopy. However, although an account of the C25 HBIs produced by Haslea species and P. intermedium would appear to be well defined, the situation with R. setigera is less clear.

Here, we describe an investigation into the distribution of C25 and C30 HBI alkenes biosynthesised by R. setigera as a function of the position of the cells through their life cycle. Our observations reveal a relationship between cell size and HBI content including a dramatic change in the distribution of alkenes during the regeneration of their original size through a sexual cycle (auxosporulation).

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