HR: 1340h
AN: B33B-0262    [Abstracts]
TI: Targeted genomic discovery of biosynthetic pathways: Anaerobic synthesis of hopanoids by {\it Geobacter sulfurreducens}
AU: * Fischer, W W
EM: wfischer@fas.harvard.edu
AF: Department of Earth and Planetary Sciences Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Summons, R E
EM: rsummons@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology, E34-246, 42-44 Carleton Street, Cambridge, MA 02139 United States
AU: Pearson, A
EM: pearson@eps.harvard.edu
AF: Department of Earth and Planetary Sciences Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AB: The biomarker concept requires that preservable molecules (molecular fossils) carry specific taxonomic and/or metabolic information. Initially, an empirical approach was used to discover which compounds are produced by certain taxa. These observations provided the basis for the interpretation of biomarkers in modern environments and the geologic record. Now, with the rapid sequencing of hundreds of microbial genomes, a more focused genomic approach can be taken to test phylogenetic patterns and hypotheses. To deduce whether specific compounds are indeed taxonomic (and metabolic) markers, candidate organisms can be selected for study on the basis of genes that encode proteins fundamental to the synthesis of certain biomarkers. Hopanoids, a class of pentacyclic triterpenoid lipid biomarkers, provide an illustrative example. For the past twenty years, biomarker studies have worked under the assumption that hopanoids are only produced by aerobic organisms. But the discovery of isotopically-depleted hopanoids in environments of anaerobic methane oxidation suggests that some hopanoids are produced anaerobically. To test these ideas we searched publicly-available genomic databases using squalene-hopene cyclase (a fundamental enzyme responsible for hopanoid biosynthesis) sequences from known hopanoid producers to find a candidate organism potentially capable of anaerobic hopanoid biosynthesis. Here we present evidence from a pure culture that {\it Geobacter sulfurreducens}, a bacterium common in anoxic environments, has the appropriate genes for hopanoid biosynthesis and produces a wide variety of complex hopanoids under strictly anaerobic conditions.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting