HR: 08:40h
AN: B31D-03    [Abstracts]
TI: On the Significance of Bacterial triterpenic Biomarkers in Sediments
AU: * Rohmer, M
EM: mirohmer@chimie.u-strasbg.fr
AF: Universite Louis Pasteur, Institut Le Bel 4 rue Blaise Pascal, Strasbourg, 67070 France, Metropolitan
AB: Triterpenic biomarkers are ubiquitous in the organic matter of sediments. Bacterial contribution is essential for several series. Despite the numerous investigations performed over the last decades, little is known about the distribution of triterpenoids in Eubacteria. An updated survey of triterpene distribution in Eubacteria points out a much broader diversity of the structures than expected ten years ago. Hopanoids characterized by their C35 skeleton resulting from a carbon/carbon linkage between the triterpene hopane skeleton and a D-ribose derivative are the most frequent ones. Their distribution cannot be readily interpreted and may result from lateral gene transfer. Many groups, such as strict anaerobes, are underrepresented in the screenings, mainly because of the complex techniques required for their growth. Most of the bacterial hopanoids belong to the (17$\alpha$H,21$\beta$H) series, corresponding to the stereochemistry of hopanoid biomarkers from non-mature sediments. (17$\beta$H,21$\alpha$H)- and especially (17$\alpha$,21$\beta$H)-hopanoids are derived from the former series via diagenesis and maturation of the organic matter. Both series were, however, recently found in widespread soil bacteria ({\it Frankia} spp., {\it Geodermatophilus} spp.) questioning at least partially their significance as maturation indicators. Quasi-hopanoids with the gammacerane skeleton were first found in ciliate protozoa. They are also present in high concentrations in the phylogenetically related bacteria {\it Rhodopseudomonas palustris} and all {\it Bradyrhizobium} spp. In all closely investigated hopanoid producing bacteria, a complex mixture of triterpene hydrocarbons accompanied in small amounts hop-22(29)-ene. They include pentacyclic triterpenes (rearranged hopenes, fernenes) as well as tetracyclic triterpenes (dammaradienes, euphadienes) and result from a lack of strict control of the cyclization process by the squalene/hopene cyclase. Triterpenoids related to sterol biosynthesis (lanosterol, cycloartenol) have been found in a few scattered taxa. Their contribution to the sediment biomarkers is not obvious. Finally, the reactions leading from biohopanoids to the geohopanoids are poorly known. Only evidence for abiotic degradation rather than for biological degradation is available.
DE: 4840 Microbiology
DE: 1055 Organic geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting