Effects of auxosporulation on distributions of C25 and C30 isoprenoid alkenes in Rhizosolenia setigera

The effect of life cycle on the distributions of C25 and C30highly branched isoprenoid (HBI) alkene lipids has been investigated for the marine diatom Rhizosolenia setigera. The concentrations of the C30 compounds are largely independent of the cell volume, though the ratios of the individual isomers possessing five and six double bonds show a dependence on the position of the cell during its life cycle, especially during auxosporulation. In contrast to the C30 pseudo-homologues, the C25 isomers are not always detected in cultures of R. setigera. The biosynthesis of the C25 HBIs would appear to result from the onset of auxosporulation, with further changes to their distributions taking place after this phase, including the formation of more unsaturated isomers. The results of this investigation may be used in part to explain the large variations in these lipids reported previously.