A microbial oasis in the hypersaline Atacama subsurface discovered by a life detector chip: implications for the search for life on Mars

The Atacama Desert has long been considered a good Mars analogue for testing instrumentation for planetary exploration, but very few data (if any) have been reported about the geomicrobiology of its salt-rich subsurface. We performed a Mars analogue drilling campaign next to the Salar Grande (Atacama, Chile) in July 2009, and several cores and powder samples from up to 5?m deep were analyzed in situ with LDChip300 (a Life Detector Chip containing 300 antibodies). Here, we show the discovery of a hypersaline subsurface microbial habitat associated with halite-, nitrate-, and perchlorate-containing salts at 2?m deep. LDChip300 detected bacteria, archaea, and other biological material (DNA, exopolysaccharides, some peptides) from the analysis of less than 0.5?g of ground core sample. The results were supported by oligonucleotide microarray hybridization in the field and finally confirmed by molecular phylogenetic analysis and direct visualization of microbial cells bound to halite crystals in the laboratory. Geochemical analyses revealed a habitat with abundant hygroscopic salts like halite (up to 260?g kg(-1)) and perchlorate (41.13?μg g(-1) maximum), which allow deliquescence events at low relative humidity. Thin liquid water films would permit microbes to proliferate by using detected organic acids like acetate (19.14?μg g(-1)) or formate (76.06?μg g(-1)) as electron donors, and sulfate (15875?μg g(-1)), nitrate (13490?μg g(-1)), or perchlorate as acceptors. Our results correlate with the discovery of similar hygroscopic salts and possible deliquescence processes on Mars, and open new search strategies for subsurface martian biota. The performance demonstrated by our LDChip300 validates this technology for planetary exploration, particularly for the search for life on Mars.     

Assessing antibody microarrays for space missions: effect of long-term storage, gamma radiation, and temperature shifts on printed and fluorescently labeled antibodies

Antibody microarrays are becoming frequently used tools for analytical purposes. A key factor for optimal performance is the stability of the immobilized (capturing) antibodies as well as those that have been fluorescently labeled to achieve the immunological test (tracers). This is especially critical for long-distance transport, field testing, or planetary exploration. A number of different environmental stresses may affect the antibody integrity, such as dryness, sudden temperature shift cycles, or, as in the case of space science, exposure to large quantities of the highly penetrating gamma radiation. Here, we report on the effect of certain stabilizing solutions for long-term storage of printed antibody microarrays under different conditions. We tested the effect of gamma radiation on printed and freeze- or vacuum-dried fluorescent antibodies at working concentrations (tracer antibodies), as well as the effect of multiple cycles of sudden and prolonged temperature shifts on the stability of fluorescently labeled tracer antibody cocktails. Our results show that (i) antibody microarrays are stable at room temperature when printed on stabilizing spotting solutions for at least 6 months, (ii) lyophilized and vacuum-dried fluorescently labeled tracer antibodies are stable for more than 9 months of sudden temperature shift cycles (-20°C to 25°C and 50°C), and (iii) both printed and freeze- or vacuum-dried fluorescent tracer antibodies are stable after several-fold excess of the dose of gamma radiation expected during a mission to Mars. Although different antibodies may exhibit different susceptibilities, we conclude that, in general, antibodies are suitable for use in planetary exploration purposes if they are properly treated and stored with the use of stabilizing substances.     

Protein Microarrays-Based Strategies for Life Detection in Astrobiology

The detection of organic molecules of unambiguous biological origin is fundamental for the confirmation of present or past life. Planetary exploration requires the development of miniaturized apparatus for in situ life detection. Analytical techniques based on mass spectrometry have been traditionally used in space science. Following the Viking landers, gas chromatography-mass spectrometry (GC-MS) for organic detection has gained general acceptance and has been used successfully in the Cassini–Huygens mission to Titan. Microfluidics allows the development of miniaturized capillary electrophoresis devices for the detection of important molecules for life, like amino acids or nucleobases. Recently, a new approach is gaining acceptance in the space science community: the application of the well-known, highly specific, antibody–antigen affinity interaction for the detection and identification of organics and biochemical compounds. Antibodies can specifically bind a plethora of structurally different compounds of a broad range of molecular sizes, from amino acids level to whole cells. Antibody microarray technology allows us to look for the presence of thousands of different compounds in a single assay and in just one square centimeter. Herein, we discuss several important issues—most of which are common with other instruments dealing with life signature detection in the solar system—that must be addressed in order to use antibody microarrays for life detection and planetary exploration. These issues include (1) preservation of biomarkers, (2) the extraction techniques for biomarkers, (3) terrestrial analogues, (4) the antibody stability under space environments, (5) the selection of unequivocal biomarkers for the antibody production, or (6) the instrument design and implementation.     

Annealing of Hg2Cl2 crystals — Project of the experiment

The creep of polycrystalline Hg₂X₂ (where X = Cl, Br, J) under the terrestrial and space conditions is studied in the present experiment. The authors suppose that the creep of the Hg₂X₂ cylindrical sample can be studied by the help of the theory of micropolar (non-Newtonian) fluids. In accordance with this theory we obtain the flux of fluid through any cross-section as functions of the radius, viscosity coefficients, the gradient of pressure and the gravity acceleration. In this paper a comparison of the theoretical results for normal and zero- gravity conditions is given. It is shown that the annealing of materials having a broad region of plasticity under microgravity conditions can lead to great improvement in optical as well as mechanical qualities of the crystal. Technical aspects of the experiment are also described.     

Microgravity effects on Drosophila melanogaster development and aging: comparative analysis of the results of the Fly experiment in the Biokosmos 9 biosatellite flight.

The results are presented of the exposure of Drosophila melanogaster to microgravity conditions during a 15-day biosatellite flight, Biokosmos 9, in a joint ESA-URSS project. The experimental containers were loaded before launch with a set of Drosophila melanogaster Oregon R larvae so that imagoes were due to emerge half-way through the flight. A large number of normally developed larvae were recovered from the space-flown containers. These larvae were able to develop into normal adults confirming earlier results that Drosophila melanogaster of a wild-type constitution can develop normally in the absence of gravity. However, microgravity exposure clearly enhances the number of growing embryos laid by the flies and possibly slows down the developmental pace of the microgravity-exposed animals. Due to some problems in the experimental set-up, this slowing down needs to be verified in future experiments. No live adult that had been exposed to microgravity was recovered from the experiment, so that no life span studies could be carried out, but adult males emerged from the recovered embyros showed a slight shortening in life span and a lower performance in other experimental tests of aging. This agrees with the results of previous experiments performed by our groups.     

Iron meteorites can support the growth of acidophilic chemolithoautotrophic microorganisms

Chemolithoautotrophy based on reduced inorganic minerals is considered a primitive energy transduction system. Evidence that a high number of meteorites crashed into the planet during the early period of Earth history led us to test the ability of iron-oxidizing bacteria to grow using iron meteorites as their source of energy. Here we report the growth of two acidophilic iron-oxidizing bacteria, Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans, on a piece of the Toluca meteorite as the only source of energy. The alteration of the surface of the exposed piece of meteorite, the solubilization of its oxidized metal constituents, mainly ferric iron, and the formation of goethite precipitates all clearly indicate that iron-meteorite-based chemolithotrophic metabolism is viable.     

Spectral signatures of photosynthesis. II. Coevolution with other stars and the atmosphere on extrasolar worlds

As photosynthesis on Earth produces the primary signatures of life that can be detected astronomically at the global scale, a strong focus of the search for extrasolar life will be photosynthesis, particularly photosynthesis that has evolved with a different parent star. We take previously simulated planetary atmospheric compositions for Earth-like planets around observed F2V and K2V, modeled M1V and M5V stars, and around the active M4.5V star AD Leo; our scenarios use Earth's atmospheric composition as well as very low O2 content in case anoxygenic photosynthesis dominates. With a line-by-line radiative transfer model, we calculate the incident spectral photon flux densities at the surface of the planet and under water. We identify bands of available photosynthetically relevant radiation and find that photosynthetic pigments on planets around F2V stars may peak in absorbance in the blue, K2V in the red-orange, and M stars in the near-infrared, in bands at 0.93-1.1 microm, 1.1-1.4 microm, 1.5-1.8 microm, and 1.8-2.5 microm. However, underwater organisms will be restricted to wavelengths shorter than 1.4 microm and more likely below 1.1 microm. M star planets without oxygenic photosynthesis will have photon fluxes above 1.6 microm curtailed by methane. Longer-wavelength, multi-photo-system series would reduce the quantum yield but could allow for oxygenic photosystems at longer wavelengths. A wavelength of 1.1 microm is a possible upper cutoff for electronic transitions versus only vibrational energy; however, this cutoff is not strict, since such energetics depend on molecular configuration. M star planets could be a half to a tenth as productive as Earth in the visible, but exceed Earth if useful photons extend to 1.1 microm for anoxygenic photosynthesis. Under water, organisms would still be able to survive ultraviolet flares from young M stars and acquire adequate light for growth.