HR: 11:05h
AN: B12A-04 INVITED     [Abstracts]
TI: Investigating the distribution, phylogeny, and evolution of polycyclic triterpenoids
AU: * Pearson, A
EM: pearson@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AU: Fischer, W W
EM: wfischer@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AU: Bosak, T
EM: tbosak@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AU: Flood Page, S R
EM: flood@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AU: Jorgenson, T R
EM: tysciguy@aol.com
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AB: For fifty years, chemists and biologists have been captivated by the stereoselective, enzymatic cyclization of squalene to form polycyclic triterpenoids. With the discovery of a complex assemblage of steranes and hopanes in rock samples of Late Archean age, this reaction also has captured much interest among geologists and paleontologists. Steranes and 2Me-hopanes indicate the presence of at least locally-oxidizing conditions at a time much earlier than a number of other redox-sensitive proxies would suggest the atmosphere contained free O2. Thus a key question arises: if cyanobacteria (and by inference oxygenic photosynthesis) had evolved, why did it take a minimum of several hundred million years before free O2 began to appear in earth surface environments? Because of this conundrum, it has been suggested that the Archean biomarkers do not constrain environmental oxygen, because originally they may have been created via an unknown anaerobic pathway (Raymond and Blankenship, 2004). This is only one of many unresolved questions: What is the most likely evolutionary origin of sterols? Do hopanes and steranes provide adequate constraints on the presence of O2 and the evolution of oxygenic photosynthesis? Do hopanoids and steroids serve different physiological roles? Are cyanobacteria the dominant producers of hopanoids in the environment? How many species of anaerobes produce hopanoids? We will present environmental sequence data for squalene-hopene cyclase (sqhC) genes obtained from microbial communities in freshwater and saltwater environments. These data are compared to sequences contained in the Sargasso Sea and Iron Mountain, CA metagenomes. Both sets of data suggest that, at present, proteobacteria are the dominant phylogenetic group responsible for producing hopanoids under both aerobic and anaerobic conditions. Reference: Raymond J, Blankenship RE (2004) Biosynthetic pathways, gene replacement and the antiquity of life. Geobiology, 2:199-203.
DE: 0424 Biosignatures and proxies
DE: 0444 Evolutionary geobiology
DE: 0448 Geomicrobiology
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 4850 Marine organic chemistry (0470, 1050)
SC: Biogeosciences [B]
MN: Fall Meeting 2005