Simulations of Prebiotic Chemistry under Post-Impact Conditions on Titan.

The problem of how life began can be considered as a matter of basic chemistry. How did the molecules of life arise from non-biological chemistry? Stanley Miller's famous experiment in 1953, in which he produced amino acids under simulated early Earth conditions, was a huge leap forward in our understanding of this problem. Our research first simulated early Earth conditions based on Miller's experiment and we then repeated the experiment using Titan post-impact conditions. We simulated conditions that could have existed on Titan after an asteroid strike. Specifically, we simulated conditions after a potential strike in the subpolar regions of Titan that exhibit vast methane-ethane lakes. If the asteroid or comet was of sufficient size, it would also puncture the icy crust and bring up some of the subsurface liquid ammonia-water mixture. Since, O'Brian, Lorenz and Lunine showed that a liquid water-ammonia body could exist between about 102-104 years on Titan after an asteroid impact we modified our experimental conditions to include an ammonia-water mixture in the reaction medium. Here we report on the resulting amino acids found using the Titan post-impact conditions in a classical Miller experimental reaction set-up and how they differ from the simulated early Earth conditions.

Pavilion lake microbialites: morphological, molecular and biochemical evidence for a cold-water transition to colonial aggregates.

The presence of microbialite structures in a freshwater, dimictic mid-latitudelake and their establishment after the last ice age about 10,000 years ago is puzzling.Freshwater calcite microbialites at Pavilion Lake, British Columbia, Canada, consist of acomplex community of microorganisms that collectively form large, ordered structuredaggregates. This distinctive assemblage of freshwater calcite microbialites was studied through standard microbial methods, morphological observations, phospholipid fatty acid(PLFA) analysis, DNA sequencing and the identification of quorum sensing molecules.Our results suggest that the microbialites may represent a transitional form from theexclusively prokaryotic colonial precursors of stromatolites to the multicellular organismicaggregates that give rise to coral reefs.

A two-tiered approach to assessing the habitability of exoplanets.

In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability. The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time. The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature. For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions. As such, the PHI requires more detailed knowledge than is available for any exoplanet at this time. However, future missions such as the Terrestrial Planet Finder will collect this information and advance the PHI. Both indices are formulated in a way that enables their values to be updated as technology and our knowledge about habitable planets, moons, and life advances. Applying the proposed metrics to bodies within our Solar System for comparison reveals two planets in the Gliese 581 system, GJ 581 c and d, with an ESI comparable to that of Mars and a PHI between that of Europa and Enceladus.

Testing the H2O2-H2O hypothesis for life on Mars with the TEGA instrument on the Phoenix lander.

In the time since the Viking life-detection experiments were conducted on Mars, many missions have enhanced our knowledge about the environmental conditions on the Red Planet. However, the martian surface chemistry and the Viking lander results remain puzzling. Nonbiological explanations that favor a strong inorganic oxidant are currently favored (e.g., Mancinelli, 1989; Plumb et al., 1989; Quinn and Zent, 1999; Klein, 1999; Yen et al., 2000), but problems remain regarding the lifetime, source, and abundance of that oxidant to account for the Viking observations (Zent and McKay, 1994). Alternatively, a hypothesis that favors the biological origin of a strong oxidizer has recently been advanced (Houtkooper and Schulze-Makuch, 2007). Here, we report on laboratory experiments that simulate the experiments to be conducted by the Thermal and Evolved Gas Analyzer (TEGA) instrument of the Phoenix lander, which is to descend on Mars in May 2008. Our experiments provide a baseline for an unbiased test for chemical versus biological responses, which can be applied at the time the Phoenix lander transmits its first results from the martian surface.

Mariner mutagenesis of Brucella melitensis reveals genes with previously uncharacterized roles in virulence and survival.

BACKGROUND: Random gene inactivation used to identify cellular functions associated with virulence and survival of Brucella spp has relied heavily upon the use of the transposon Tn5 that integrates at G/C base pairs. Transposons of the mariner family do not require species-specific host factors for efficient transposition, integrate nonspecifically at T/A base pairs, and, at a minimum, provide an alternative approach for gene discovery. In this study, plasmid vector pSC189, containing both the hyperactive transposase C9 and transposon terminal inverted repeats flanking a kanamycin resistance gene, were used to deliver Himar1 transposable element into the B. melitensis genome. Conjugation was performed efficiently and rapidly in less than one generation in order to minimize the formation of siblings while assuring the highest level of genome coverage. RESULTS: Although previously identified groups or classes of genes required for virulence and survival were represented in the screen, additional novel identifications were revealed and may be attributable to the difference in insertion sequence biases of the two transposons. Mutants identified using a fluorescence-based macrophage screen were further evaluated using gentamicin-based protection assay in macrophages, survival in the mouse splenic clearance model and growth in vitro to identify mutants with reduced growth rates. CONCLUSION: The identification of novel genes within previously described groups was expected, and nearly two-thirds of the 95 genes had not been previously reported as contributing to survival and virulence using random Tn5-based mutagenesis. The results of this work provide added insight with regard to the regulatory elements, nutritional demands and mechanisms required for efficient intracellular growth and survival of the organism.