HR: 1340h
AN: PP43B-1259    [Abstracts]
TI: Do geostable polycyclic isoprenoids record the rise of oxygen in the ancient atmosphere?
AU: * BOSAK, T
EM: tbosak@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
AU: Losick, R
EM: losick@mcb.harvard.edu
AF: Department of Molecular and Cell Biology, Harvard University, Cambridge, MA 02138, United States
AU: Pearson, A
EM: pearson@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, United States
AB: Polycyclic terpenoids are among the most stable and abundant lipid compounds in sediments of all ages. They may record the composition of microbial communities and environmental conditions in the past, including the rise of molecular oxygen 2.7 billion years ago. A great deal is known about how some of these lipids are produced by the enzymatic cyclization of linear terpenoids by a family of triterpene cyclases, but whether and how specific polycyclic compounds reflect certain metabolisms or physiologies of modern microbes is not well understood. Here we demonstrate that a novel class of tetracyclic terpenoids is present in the spores of B. subtilis. These compounds are derived from the enzymatic cyclization of regular linear terpenoids by a protein homologous to known triterpenoid cyclases. The cyclization of regular linear terpenoids is thought to have produced the most ancient polycyclic terpenoids but, until now, there have not been any known modern microbial sources of such compounds. The presence of tetracyclic terpenoids increases the resistance of spores to hydrogen peroxide, a reactive oxygen species, establishing for the first time a physiological function of bacterial polycyclic terpenoids in vivo. Our work demonstrates that some polycyclic terpenoids play a direct role in protecting modern bacteria from reactive oxygen species. Similarly, their geostable derivatives in the rock record may imply the presence of oxidative stress related to the oxygenation of Earth's surface in the past.
DE: 0424 Biosignatures and proxies
DE: 0448 Geomicrobiology
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting