HR: 1340h
AN: PP43B-1281    [Abstracts]
TI: Diversity of squalene-hopene cyclases in a tropical carbonate-rich environment
AU: Leavitt, W D
EM: wleavitt@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St, Cambridge, MA 02138, United States
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
AB: Hopanoids are isoprenoid lipids which derive primarily from bacteria and are ubiquitous in contemporary Earth surface environments. In the geologic record, hopanes found in sedimentary rocks are used as proxies to help decipher ancient biological communities. However, in contrast to the ubiquity of these lipid products, biosynthesis of hopanoids appears to be a relatively rare physiological trait among bacteria in complex environmental communities. We have recently estimated that fewer than one in ten bacterial cells in soils and fewer than one in twenty bacterial cells in the ocean contains the gene squalene-hopene cyclase (sqhC) [1]. Biosynthesis of hopanoids is rarer in natural communities than it is among species that have been propagated in pure culture [2]. Here we continue our previous work to survey the phylogeny and diversity of hopanoid producers using culture-independent methods. In particular, genes affiliated with known cyanobacterial sequences were not detected in the contemporary environments analyzed previously [1]. One possible explanation is that hopanoid-producing strains of cyanobacteria are regionally localized. It has been suggested that throughout the long-term sedimentary record there is a correlation between 2-methylhopanoid index (a putative indicator of cyanobacterial biomass) and the global prevalence of shallow carbonate platform environments [3], and in previous work we did not analyze any such environments. To address this question we surveyed a land-sea gradient across the Bahamian island of San Salvador. Samples were taken from upland soil, a hypersaline lake, a tidal creek, and the shallow open ocean. The data are remarkably similar to our previous results: environmental sqhCs average < 65% translated amino acid identity to their closest relatives in public databases, and non- cyanobacterial sequences continue to dominate. We will discuss the challenges these results pose for deciphering the global distribution of microbially-derived lipids from complex communities, and we will propose some future directions forward. [1] Pearson A, Flood Page SR, Jorgenson TL, Fischer WW, Higgins MB (2007) Novel hopanoid cyclases from the environment. Environmental Microbiology 9, 2175-2188. [2] Rohmer M, Bouvier-Nave P, Ourisson G (1984) Distribution of hopanoid triterpenes in Prokaryotes. J. Gen. Microbiol. 130, 1137-1150. [3] Summons, RE (personal communication).
DE: 0424 Biosignatures and proxies
DE: 0444 Evolutionary geobiology
DE: 0448 Geomicrobiology
DE: 1055 Organic and biogenic geochemistry
DE: 4850 Marine organic chemistry (0470, 1050)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting