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A more complete picture of life on Earth, and even life in the Earth, has recently become possible through the application of environmental genomics. We have obtained the complete genome sequence of a new genus of the Finnicutes, the uncultivated sulfate reducing bacterium Desulforudis audaxviator, by filtering fracture water from a borehole at 2.8 km depth in a South African gold mine. The DNA was sequenced using a combination of Sanger sequencing and 454 pyrosequencing, and asserrlbled into just one genome, indicating the planktonic community is extremely low in diversity. We analyzed the genome of D. audaxviator using the MicrobesOnline annotation pipeline and toolkit (http://www.microbesonline.org), which offers powerful resources for comparative genome analysis, including operon predictions and treebased comparative genome browsing. MicrobesOnline allowed us to compare the D. audaxviator genome with other sequenced members of the Firmicutes in the same clade (primarily Pelotomaculum thennoproprionicum, Desulfotomaculum reducens, Carboxydothennus hydrogenoformans, and Moorella thennoacetica), as well as other known sulfate reducers and thermophilic organisms. D. audaxviator gives a view to the set of tools necessary for what appears to be a self-contained, independent lifestyle deep in the Earth's crust. The genome is not very streamlined, and indicates a motile, endospore forming sulfate reducer with pili that can fix its own nitrogen and carbon. D. audaxviator is an obligate anaerobe, and lacks obvious homologs of many of the traditional 02 tolerance genes, consistent with the low concentration of O2 in the fracture water and its long-term isolation from the surface. D. audaxviator provides a complete genome representative of the Gram-positive bacteria to further our understanding of dissimilatory sulfate reducing bacteria and archaea. Additionally, study of the deep subsurface has offered access to the simplest community yet studied by environmental genomics, perhaps consisting of just a single species that is capable of performing all of the tasks necessary for life.

A more complete picture of life on Earth, and even life in the Earth, has recently become possible through the application of environmental genomics. We have obtained the complete genome sequence of a new genus of the Firmicutes, the uncultivated sulfate reducing bacterium Desulforudis audaxviator, by filtering fracture water from a borehole at 2.8 km depth in a South African gold mine. The DNA was sequenced at the JGI using a combination of traditional Sanger sequencing and 454 pyrosequencing, and assembled into just one genome, indicating the planktonic community is extremely low in diversity. We analyzed the genome of D. audaxviator using the MicrobesOnline annotation pipeline and toolkit (http://www.microbesonline.org, and see MicrobesOnline abstract), which offers powerful resources for comparative genome analysis, including operon predictions and tree-based comparative genome browsing. MicrobesOnline allowed us to compare the D. audaxviator genome with other sequenced members of the Firmicutes in the same clade (primarily Pelotomaculum thermoproprionicum, Desulfotomaculum reducens, Carboxydothermus hydrogenoformans, and Thermoanaerobacter tengcongensis), as well as other known sulfate reducers (including Archaeoglobus fulgidus and Desulfovibrio vulgaris). D. audaxviator gives a view to the set of tools necessary for what appears to be a self-contained, independent lifestyle deep in the Earth's crust. The genome is not very streamlined, and indicates a motile, endospore forming sulfate reducer with pili that can fix its own nitrogen and carbon. D. audaxviator is an obligate anaerobe, and lacks obvious homologs of many of the traditional O2 tolerance genes, consistent with the low concentration of O2 in the fracture water and its long-term isolation from the surface. D. audaxviator provides a complete genome representative of the Gram-positive bacteria to further our understanding of dissimilatory sulfate reducing bacteria and archaea, and offers the full complement of genes necessary for an independent lifestyle based solely on interactions with the geochemistry of the deep subsurface.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.11.028 Byline: Adam P. Johnson (a), Lisa M. Pratt (b) Keywords: Exobiology; Photochemistry; Geological processes; Mars Abstract: Recent lines of evidence indicate that Mars may have been substantially warmer and wetter, raising questions about whether the planet's surface was once more conducive to the possibility of life. To better constrain the extent of preservation of ancient amino acid biosignatures, the effects of metal ions and UV radiation were investigated with respect to the rates of diagenesis of amino acids in metal-rich sulfate brines. Individual experimental results indicate that the oxidation rates of amino acids loosely followed trends characteristic of a radiolytic oxidation mechanism that is dependent on variations in side-chain constituents. Relative rates of racemization only show a limited dependence on the presence of metals; overall, rates of racemization in the presence of metals in solution are an order of magnitude slower than oxidation and both are several orders of magnitude faster than previously reported. This increase in rate constant is indicative of an extremely efficient catalytic enhancement of this destructive diagenetic pathway. These findings imply that chiral life-detection strategies should focus on specific geochemical environments that exhibit relatively slow rates of both degradation and racemization. Episodic liquid water during periods of increased water activity on the martian surface may have significant implications for the oxidation of organic matter through secondary diagenetic reactions and may act as a leveling mechanism for organic compounds. Author Affiliation: (a) Department of Molecular and Cellular Biochemistry, Indiana University, 1001 E. 10th Street, Bloomington, IN 47405, United States (b) Department of Geological Sciences, Indiana University, 1001 E. 10th Street, Bloomington, IN 47405, United States Article History: Received 6 April 2009; Revised 5 November 2009; Accepted 24 November 2009

Intense fluctuations in precipitation govern seasonal cycles of ephemeral lakes, controlling hydration stresses and producing changes in the biochemical composition of endemic microbes. The lipid compositions of emergent and desiccated mats with comparable microbial communities from evaporative alkaline lakes reveal increases in the abundance and average chain length of wax esters (WE) that may represent an evolutionary strategy to survive desiccation in evaporative environments. Subsequent rehydration naturally saponifies WE, regenerating alcohol and acid moieties that can be utilized as membrane lipids for the next viable microbial generation. The antiquity of this biosynthetic innovation suggests that WE production likely facilitated microbial migration to lake environments in the earliest terrestrial ecosystems as well as their survival through hydration-dehydration cycles. doi: 10.1130/G30398.1

Sulfur isotope analysis ([[delta].sup.34]S) of well-preserved carbonates spanning an ~10 Ma interval of the terminal Proterozoic Nama Group reveals that disseminated pyrite is consistently enriched in [sup.34]S relative to coeval seawater sulfate as preserved in carbonate-associated sulfate (CAS). This observation is not consistent with the current paradigm for interpreting the geologic record of sulfur isotopes, which assumes that pyrite [[delta].sup.34]S ([[delta].sup.34][S.sub.pyr]) will be equal to or less than co-occurring CAS [[delta].sup.34]S ([[delta].sup.34][S.sub.CAS]) due to the kinetic isotope effect of bacterial sulfate reduction (BSR) that favors the lighter isotope of sulfur ([sup.32]S) during sulfur-oxygen bond breakage. Although the precise mechanism of pyrite sulfur isotope enrichment is debatable, our combined observations of extremely [sup.34]S-enriched pyrite, low bulk-rock concentrations of sulfur from CAS and pyrite, and high-frequency fluctuations in [[delta].sup.34][S.sub.CAS] and [[delta].sup.34][S.sub.pyr] throughout the Nama Group carbonates point to very low concentrations of sulfate in portions of the terminal Proterozoic ocean. The additional occurrence of [sup.34]S-enriched pyrite in contemporaneous terminal Proterozoic sections from Poland and Canada reveal that low seawater sulfate may have been widespread in the oceans at this time. However, the absence of such extremely [sup.34]S-enriched pyrite from well-preserved, coeval carbonate sections in Oman suggests that such conditions were not globally uniform. Low, geographically varied concentrations of marine sulfate in terminal Proterozoic time are consistent with elevated, geographically varied concentrations of reactive, nonpyritized iron in marine shales recently reported for this interval, suggesting that high dissolved Fe(II) and low [O.sub.2] persisted in a range of marine facies as late as 543 Ma--tens of millions of years after the origin of animals, yet prior to their major diversification in Early Cambrian time.

Alkaline, sulfidic, 4 to 53 million-year-old meteoric water emanating from a borehole intersecting quartzite-hosted fractures greater than 3.3 kilometer beneath the surface have supported a microbial community dominated by a bacterial species with Desulfotomaculum spp. and an archaeal species related to Methanobacterium spp. These geochemical setting and microbial communities are notably different from microbial ecosystems reported for shallower continental subsurface environments.