HR: 09:15h
AN: B31D-05    [Abstracts]
TI: The Evolution of Sterol Biosynthesis in Bacteria: In Situ Fluorescence Localization of Sterols in the Nucleoid Bacterium {\it Gemmata obscuriglobus}
AU: * Budin, M
EM: budin@fas.harvard.edu
AF: Harvard University Department of Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138 United States
AU: Jorgenson, T L
EM: tyler.jorgenson@asu.edu
AF: Harvard University Department of Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138 United States
AU: Pearson, A
EM: pearson@eps.harvard.edu
AF: Harvard University Department of Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138 United States
AB: The biosynthesis of sterols is generally regarded as a eukaryotic process. The first enzymatic step in the production of sterols requires molecular oxygen. Therefore, both the origin of eukaryotes and the evolution of sterol biosynthesis were thought to postdate the rise of oxygen in earth's atmosphere, until Brocks et al. discovered steranes in rocks aged 2.7 Ga (1). Many prokaryotes produce hopanoids, sterol-like compounds that are synthesized from the common precursor squalene without the use of molecular oxygen. However, a few bacterial taxa are also known to produce sterols, suggesting this pathway could precede the rise of oxygen (2, 3). Recently, we discovered the shortest sterol-producing biosynthetic pathway known to date in the bacterium {\it Gemmata obscuriglobus} (4). Using genomic searches, we found that {\it Gemmata} has the enzymes necessary for synthesis of sterols, and lipid analyses showed that the sterols produced are lanosterol and its isomer parkeol. {\it Gemmata} is a member of the Planctomycetes, an unusual group of bacteria, all of the known species of which contain intracellular compartmentalization. Among the Planctomycetes, {\it Gemmata} uniquely is the only prokaryote known to contain a double-membrane-bounded nuclear body (5). Since sterols usually are found in eukaryotes, and {\it Gemmata} has a eukaryote-like nuclear organelle, we investigated the location of the sterols within {\it Gemmata} to postulate whether they play a role in stabilization of the nuclear membrane and control of genomic organization. We used the sterol-specific fluorescent dye Filipin III in conjunction with fluorescent dyes for internal and external cellular membranes in order to determine whether the sterols are located in the nuclear body membrane, external membrane, or both. We found that sterols in {\it Gemmata} are concentrated in the internal membrane, implying that they function in maintaining this unusual cellular component. It is notable that {\it Gemmata} also produce hopanoids, suggesting that they acquired the ability to produce sterols for a specialized function related to their nuclear membrane. 1. Brocks, J.J., et al., Science 285:1033-36 (1999). 2. Bird, C.W., et al., Nature 230:473-74 (1971). 3. Bode, H.B., et al., Mol. Microbiol. 47:471-81 (2003). 4. Pearson, A., et al., Proc. Natl. Acad. Sci. USA 100:15352-57 (2003). 5. Fuerst, J.A. and R.I. Webb, Proc. Natl. Acad. Sci. USA 88:8184-88 (1991).
DE: 4840 Microbiology
DE: 1055 Organic geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting