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Proceedings Volume 6694, including the Title Page, Copyright
information, Table of Contents, and the
Conference Committee listing.
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I have proposed a model, in which adenosine triphospate (ATP) plays a key role in prebiological evolution. Life is a
phenomenon of evolving ordering. It can be shown that a system of conjugated irreversible reactions supplied by energy
and dwelling near a steady state, is charged to produce ordering. ATP has properties which are the most appropriate to
be involved in such a system. Primary synthesis of ATP demands strong reduced conditions. I show here that such
conditions may exist on the early Earth.
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Assuming an extra-terrestrial formation of life's molecular building blocks such as amino-acids, a possible abiotic
explanation for the selection of the L enantiomers could be the exposure to an asymmetric bias such as far UV Circularly
Polarized Light (CPL), during their journey towards Earth, inducing some enantiomeric excess (e.e) that could then be
amplified on Earth via suitable autocatalytic mechanisms. Synchrotron Radiation (SR), with its intense flux and broad
tunability, is a unique tool which mimics such an interstellar far UV CPL. We have recently employed it to study : (1)
The irradiation of solid films of the amino acid D,L-leucine, i.e. under relevant astrophysical conditions. Starting from
racemic D,L-leucine irradiated with CPL SR beam at 6.8 eV (182 nm), we have been able to induce by enantioselective
photolysis an e.e. of 2.6 %, as measured by chiral-sensitive CG-MS analysis, in accordance with the CD spectrum
recorded on the same type of sample. (2) CPL-induced gas phase photoionization of chiral molecules. By measuring the
angular distribution of photoelectrons ejected from pure enantiomers, we observed a strong anisotropy (up to 16 %) in
the forward/backward direction with respect to the light propagation axis. Because of momentum conservation, such an
effect is accompanied by an asymmetric recoil of the corresponding ions that could lead to a high e.e. Future prospects
on the new VUV SR beamline DESIRS at SOLEIL are presented.
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Frank Tipler, in The Physics of Immortality, wrote about how to spread a form of traveling artificial life throughout the
known, expanding universe, prior to collapse. The key is to make the ALife self-reproducing, permitting exponential
growth, like life itself, but faster. We ask whether microbial extremophiles could have originated in a single location at
an early phase of a big bang universe, and spread throughout the cosmos, as is commonly assumed in discussions of the
panspermia hypothesis? Since the universe was much smaller when the first condensed matter appeared, this hypothesis
merits consideration. In comparing particle horizons with biohorizons, we find that the answer is no: at our earliest
estimated time for the origin of life, 500x106 years after the big bang, if life started everywhere it could, there would
have had to have been at least 50,000 origins of life. In the course of our rough calculations, we introduce the concepts
of the generations of life (from microorganisms to consciousness), the Biocosmological Principle that life is spread
throughout the universe, life as a wave in an active medium, and the speed of life, i.e., the speed of ejecta from galaxies and lesser bodies on which life could be transported.
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We have found that alcohols catalyze a rapid polymerization of silicic acid to silica gel upon the addition of alcohols.
Like amino acids, alcohols could be preserved in the silica gel by two mechanisms. In the first mechanism, the alcohols
become entombed in the silica gel. In this case, only Si-O-Si bonds would be observed in the infrared (IR) spectra. In
the second mechanism, the alcohols make chemical bonds with the silicic acid, to create organo-silicates. In this case,
Si-O-C bonds would be observed in the IR. We have found that steric hindrance plays a major role in the volume of an
alcohol required. Amino alcohols are more effective in creating a viscous gel than the alcohols, and appeared to form
covalent Si-O-C bonds in some cases. Characteristic shifts in the Si-O-Si bands of over 50 cm-1 towards lower IR
frequencies can be observed in the alcohol gels. The hydrolysis of known organo-silicates has led to the identification
of the Si-O-C band in the region of 1225-1150 cm-1, and the Si-O-Si band in the region of 1125-1000 cm-1.
Alcohols play an important role in many biological pathways, and could serve as biosignatures in extreme environments including meteorites and other planets.
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This article intends to continue our previous work on the symbiogenic approach to chemical and biological evolution.
We believe that cooperative and synergistic processes were responsible, using terrestrial and extraterrestrial materials,
for the creation of a large prebiotic pool, closely related to geochemical contexts, and intense interactions within.
Probably, a series of synergistic and cooperative effects produced a wide source of creativity, and functional advantages
that pushed the emergence of complex and functionally integrated biological systems, through the evolution of self-organization
and auto-catalysis. It was only after this biochemical evolution of structures, which produced the
informational capabilities necessary for self-replication, that the Darwinian mechanisms could arise. This way of
perceiving the emergence of life follows the proposals regarding life's initial evolution in which the progenote proposed
consisted in an open community of very diverse primitive cellular entities with intense symbiotic associations,
antagonisms, and competition, and with a rapid and reticulate pattern of evolution. We believe this symbiogenic
approach should be considered in the understanding of chemical and biological evolution. This discussion contributes to
the development of astrobiological knowledge, since it gives other perspectives about life's appearance and development
on Earth and elsewhere.
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During the past decade, Environmental and Field Emission Scanning Electron Microscopes have been used at the
NASA/Marshall Space Flight Center to investigate freshly fractured interior surfaces of a large number of different
types of meteorites. Large, complex, microfossils with clearly recognizable biological affinities have been found
embedded in several carbonaceous meteorites. Similar forms were notably absent in all stony and nickel-iron
meteorites investigated. The forms encountered are consistent in size and morphology with morphotypes of known
genera of Cyanobacteria and microorganisms that are typically encountered in associated benthic prokaryotic mats.
Even though many coccoidal and isodiametric filamentous cyanobacteria have a strong morphological convergence
with some other spherical and filamentous bacteria and algae, many genera of heteropolar cyanobacteria have
distinctive apical and basal regions and cellular differentiation that makes it possible to unambiguously recognize the
forms based entirely upon cellular dimensions, filament size and distinctive morphological characteristics. For almost
two centuries, these morphological characteristics have historically provided the basis for the systematics and
taxonomy of cyanobacteria. This paper presents ESEM and FESEM images of embedded filaments and thick mats
found in-situ in the Murchison CM2 and Orgueil CI1 carbonaceous meteorites. Comparative images are also provided
for known genera and species of cyanobacteria and other microbial extremophiles. Energy Dispersive X-ray
Spectroscopy (EDS) indicates that the meteorite filaments typically exhibit dramatic chemical differentiation with
distinctive difference between the possible microfossil and the meteorite matrix in the immediate proximity.
Chemical differentiation is also observed within these microstructures with many of the permineralized filaments
enveloped within electron transparent carbonaceous sheaths. Elemental distributions of these embedded filaments are
not consistent with recent cyanobacteria or other living or preserved microbial extremophiles that have been
investigated during this research. The meteorite filaments often have a nitrogen content below the sensitivity level of
the EDS detector. Carbon, Sulfur, Iron or Silicon is often highly enriched and hence anomalous C/N and C/S ratios
when compared with modern cyanobacteria. The meteorite forms that are unambiguously recognizable as biological
filaments are interpreted as indigenous microfossils analogous to several known genera of modern cyanobacteria and
associated trichomic filamentous prokaryotes.
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No principal differences have been found between microfossils described from Cambrian and Phanerozoic
and the 2000 Ma phosphorites. Numerous samples revealed diverse microbial microstructures interpreted as
cyanobacterial mats consisting of filamentous (1-3 μm in diameter, 20 μm in length), coccoidal (0.8-1.0 μm) and
ellipsoidal or rod-shaped microfossils (0.8 μm in diameter, around 2 μm in length) which morphologically resemble
modern Microcoleus and Siphonophycus, Thiocapsa, and Rhabdoderma, respectively, reported from alkaline or
saline environments. The sequence of the early Palaeoproterozoic events which point to a significant oxidation of the
hydrosphere, including the formation of phosphorites and changes in the phosphorous cycle, mimics the sequence
which was repeated at the Neoproterozoic-Cambrian transition, implying that oxidation of the terrestrial atmosphere-hydrosphere
system experienced an irregular cyclic development.
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We show that radiogenic heating in primordial comets of radii in excess of ~10km could produce liquid water cores
persisting for hundreds of thousands to millions of years. Supposing comets were seeded with even the smallest
numbers of viable microbes at the time of their formation from pre-solar material, there is ample time for exponential
amplification within the liquid interiors before refreezing occurs. Freeze-dried biological material is returned to
interplanetary and interstellar space during cometary activity as the outer layers of comets are stripped away via
sublimation. Modelling of the post-impact 8-12μm spectra of Tempel 1 gives a strong indication of mixtures of clays
and organics in comparable quantity, clays in turn providing evidence of a liquid water history of the comet. The totality
of comets in a galaxy or a cluster of galaxies, seems to provide a far more promising setting for an origin of life than any
setting thus far proposed in relation to the primitive Earth. Once life has originated in a comet mechanisms of interstellar
panspermia that have recently been identified will disperse throughout the Galaxy within a few billion years.
Keywords: Comets, liquid water, clay, organics, origin of life, panspermia
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Secular changes in the stable sulfur isotope composition of seawater sulfate on Earth range from approximately 25 to 30
per mil (CDT). Minimal fractionation has been observed for the direct assimilation of seawater sulfate by plants into the
two sulfur containing protein amino acids, methionine and cysteine. Similarly, sulfur isotope fractionation appears to be
minimal with increasing trophic level. Thus, in theory, secular changes in the stable sulfur isotope composition of sulfur
containing amino acids in ancient marine organisms should mimic that of seawater sulfate. The presence of sulfur
containing amino acids elsewhere in the solar system and a comparison of their respective stable sulfur isotope values to
those of sulfate containing minerals of similar ages may provide an alternative approach for determining the occurrence
of past extraterrestrial life.
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This research documents the analysis and interpretation of selected Carbonaceous Chondrites (CC) including Murchison,
Allende, NWA 3003, Dhofar 735, Orgueil, Tagish Lake and Vigarano using organic petrology, scanning electron microscopy,
and petroleum geochemistry. The kerogen microstructures and bitumen within CCs closely resemble remnant 2.5 Ga
terrestrial microbial-like structures and their biodegraded components and solid bitumen. In both instances, organoclasts are
associated with framboidal iron sulfides or oxides and clay-like minerals. The organic-rich kerogens within three CCs
(especially Murchison) might have served as petroleum source rocks for the early generation of hydrocarbons. The maturity
varies between 0.7% (Orgueil) and 1.24% (Murchison), to 5.1 % Ro (Vigarano) with predicted maturation temperatures of
100° to 475°C. Geochemical analysis of selected CCs (Murchison, Orgueil, and Tagish Lake) reveal the organic richness and
the presence of low molecular weight n-alkanes (C10 to C20), complex cyclo-and isoalkanes, nonhydrocarbons, elemental
sulfur with abundant aromatic compounds, most of them similar to bacterial and algal derived petroleum products. Apart from
the concept of panspermia, the data highlights that three CCs sustained a formation temperature (<200°C) capable of
supporting bacterial growth in a cooler early Solar System environment. In effect, the information encoded within these
extraterrestrial sediments represents a cosmic analogue to terrestrial geopolymers and bitumen that may include some crude
oil biomarkers. Therefore, the authors propose a model of a "universal unconventional petroleum system", which implies a
prospect of oil and gas within the Martian environment and elsewhere within the Solar System.
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The ability to distinguish possible microfossils from recent biological contaminants is of great importance to
Astrobiology. In this paper we discuss the application of the ratios of life critical biogenic elements (C/O; C/N; and
C/S) as determined by Energy Dispersive X-ray Spectroscopy (EDS) to this problem. Biogenic element ratios are
provided for a wide variety of living cyanobacteria and other microbial extremophiles, preserved herbarium materials,
and ancient biota from the Antarctic Ice Cores and Siberian and Alaskan Permafrost for comparison with macrofossils
and microfossils in ancient terrestrial rocks and carbonaceous meteorites.
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The NASA Stardust mission to comet 81P/Wild-2 returned to Earth in January 2006 carrying captured cometary dust
grains. Analysis of these grains is permitting an extensive study of cometary composition to be carried out. This includes
identifying both the mineral and organic content of the captured material. Based on this, the picture emerges of a comet
whose component materials have a diverse origin and which has not undergone any extensive aqueous alteration, has a
nitrogen rich organic history, may contain amines and at least 1 amino acid and has organics which in some respects
resemble interplanetary dust particles and meteorites, in others resemble one and not the other, and in yet others are
distinct from both. In terms of astrobiology, comets as a source of organic materials for the inner Solar System clearly
have a role to play, but this cannot be fully assessed based on the history of just one comet nucleus. Nevertheless, the
positive identification of a range of organic materials in this comet significantly moves forward the discussion of organic
materials and comets.
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Recent observations of cyanobacterial fossils on carbonaceous chondrites have conclusively established the presence
of fossil organisms on extraterrestrial bodies widely presumed to be comets. Likewise, the data from four
cometary flyby (and one impact) missions and the exploration of a peculiar S-type asteroid, show evidence of liquid
water in the past or present. In addition, sand grains returned from the tail of comet P/Wild-2 demonstrate
that comets accrete inner Solar System material. So it is a short step to propose the separate and independent
existence of a cometary biosphere, the ecosystem of organisms that exploit the niche of an extraterrestrial environment.
This paper attempts to lay the framework for such a hypothetical ecosystem, and establish criteria for
its continued existence and spread.
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I review three types of related cometary phenomena, which, in the order listed, are increasingly important in studies of
cometary evolution: dust jet-like morphological features in comet heads; outbursts; and nucleus fragmentation. Gas-driven
collimated jets consisting predominantly of microscopic dust particles are a standard mode of comet activity, as has amply
been documented by numerous ground-based observations and even more convincingly by closeup images taken with the
cameras aboard the space missions that flew by four periodic comets between 1986 and 2005. Gas expanding from discrete
emission sources on or below the nucleus surface drags dust with it into the atmosphere in quantities that vary with time.
Briefly occurring sudden great enhancements of activity are known as outbursts. Dust ejecta in most outbursts do not
include larger objects than boulder-sized ones, thus limiting the total mass delivered in such episodes. At times, however,
outbursts accompany a nucleus fragmentation event, which signals a major episode. Fragmentation events have a tendency
to recur, their products offering a complex hierarchy of large fragments. A rapid sequence of fragmentation events may end
up with a sudden, complete disintegration of a significant fraction of the original comet or, more rarely, the entire comet.
Indications are that cascading fragmentation is the most efficient process of comet aging and ultimate demise.
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Biologists tacitly assume that all life on Earth descended from a common
origin. This assumption is based on biochemical similarities and gene sequencing, which
enables organisms to be positioned on a common tree of life. However, most terrestrial
organisms are microbes, and it is impossible to deduce their biochemical nature from
morphology alone. The vast majority of microbes remain unclassified, leaving open the
possibility that some of them might be an alternative form of life, arising either from an
independent origin, or representing a hitherto overlooked very ancient branch of the
known tree. Thus there may exist an extinct, or even extant, shadow biosphere. I discuss
various research proposals for locating and identifying "alien" organisms on Earth, both
ecologically separate and ecologically integrated.
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After only three years of close observation from the Cassini-Huygens mission, Titan appears more and more as one of
the key planetary bodies in the solar system for astrobiological studies. Titans does not look any more like a frozen
primitive Earth, but like an evolving planet, geologically active, with cryovolcanism, eolian erosion, clouds and
precipitations, and a methane cycle very similar to the water cycle on Earth. The new data also show a very complex
organic chemistry in the highest atmospheric zones of the satellite, with the formation in the ionosphere of high
molecular weight organics feeding the lower zones, down to the surface. In spite of the low surface temperature, these
organics are probably evolving once in contact with water ice and form organic molecules of biological interest. This
may explain the reflectance spectrum of Titan' surface observed by the DIRS instrument on Huygens. Thus, contrary to
what was expected, the organic chemistry on Titan seems mainly concentrated in the ionosphere, in the aerosols and on
the surface. These astrobiological aspects of Titan are presented and discussed on the basis of the already available
Cassini-Huygens data, as well as the needed post Cassini exploration.
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Few, if any, major scientific quests have taken such frequent, diametrically opposed changes in prospect and direction
as has the search for life on Mars. The erratic courses and their supporting rationales are traced: from Percival Lowell's
astonishing pronouncement of intelligent beings on the red planet; to their denouement by Mariner 4; to the strong
contraindications of any form of Martian life relayed by Mariners 6 and 7; to the discovery of a different, perhaps once-habitable,
Mars revealed by the detailed orbital images, including the first evidence of ancient rivers, taken by Mariner 9;
to the still-controversial claim of the detection of microbial life by the 1976 Viking Missions; to NASA's subsequent
prohibition against any Mars life detection experiments; to the recently emerged consensus, propelled by findings of
Pathfinder, the Mars Exploratory Rovers and the continuing discoveries of life in extreme environments on Earth, that
past or extant life on Mars is likely. Against this background, the future Mars missions' experiments bearing on the life
issue are reviewed. The case is made that none of these experiments, as currently planned, still subject to the
prohibition against direct life detection experiments, can resolve this paramount and fundamental question that bears so
heavily on the origin and distribution of life, and our place in the universe.
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The conditions on Mars imply an evolutionary advantage for organisms employing a mixture of H2O2 and H2O in their
intracellular fluid: the H2O2-H2O eutectic freezes at -56.5°C, is hygroscopic and a source of oxygen. Contrary to common
belief, H2O2 is used for a variety of purposes in terrestrial biochemistry. The Viking Lander Biology Experiments have often
been interpreted as the result of inorganic oxidants in the Martian soil. Here, we interpret the Viking findings as the result of
the reactions of H2O2-H2O based life. Several hitherto puzzling findings are explained by the H2O2-H2O hypothesis. The
lack of detected organics is the result of autooxidation of the organisms as these were gradually heated. Supportive
observations were made in the PR and LR experiments. Our interpretation is that the addition of water vapor at a relatively
high temperature could only be withstood by the organisms for a short time, as they perished due to hyperhydration. The
evolution of oxygen in the GEx experiment is explained by the high oxidative content of the organisms as they perished in
this experiment. The PR experimental conditions were most Mars-like and carbon assimilation could be detected but no
growth. Particularly, the GEx experiment allows the calculation of biomass in the Martian soil based on measured evolution
of reaction products. Further properties of the suggested organisms such as metabolic reactions and by-products may be
detected by future Mars missions.
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The Viking mission was the only mission to date that conducted life detection experiments. It revealed ambiguous and
still controversial results. New findings and hypotheses urge a re-evaluation of the Viking results and a re-evaluation of
the evidence for the possible presence of life on Mars in general. Recent findings of abundant water ice on Mars, the
presence of liquid contemporary water on the Martian surface, and the detection of methane in the Martian atmosphere
further support this possibility. Current missions to be launched focus on habitability considerations (e.g., NASA Phoenix,
NASA Mars Science Laboratory), but shy away from directly testing for life on Mars, with the potential exception of the
ESA ExoMars mission. If these currently planned missions collect positive evidence toward habitability and the possible
existence of extraterrestrial (microbial) life on Mars, it would be timely to propose a new mission to Mars with a strong life
detection component. We propose such a mission called BOLD: Biological Oxidant and Life Detection Mission. The
BOLD mission objective would be to quantify the amount of hydrogen peroxide existing in the Martian soil and to test
for processes typically associated with life. Six landing packages are projected to land on Mars that include a limited
power supply, a set of oxidant and life detection experiments, and a transmitter, which is able to transmit information via
an existing Mars orbiter back to Earth.
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After a picture-perfect launch to Mars on August 4, 2007, the Phoenix mission will land near 70° N on the
northern lowlands on May 25, 2008 and perform an in situ investigation of the ice layer discovered by the Mars Odyssey
scientists in 2002. Mars undergoes climate change through obliquity and orbital variations on time periods of 50,000
years. By analyzing the minerals, aqueous chemistry, and grain shapes of the soil associated with the ice, Phoenix will
determine whether the ice has ever melted and modified the soil properties. Since water is a necessary substance for life
on Earth, a major question for the mission is whether the northern plains represent a habitable zone on Mars. Besides
water. the Phoenix team will assess the organic content of the soil and ice as well as the abundances of biologically
active elements. Finally, the transport of water through soils and atmosphere is measured using a Canadian
meteorological station supplemented by probes to evaluate soil conductivity.
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The diatoms (Division Bacillariophyta) are aquatic, pigmented single-celled photosynthetic eukaryotes. They are a
major component of the food chain in marine, estuarine and freshwater ecosystems. These diploid organisms have the
ability to take dissolved silica out of the water column, and use it to create their cell walls. The taxonomy and
classification system for the group is based to a large part on cell wall symmetry, as well as the number, type, position
and organization of the many perforations in the glass. As a group, diatoms are found in almost every water type of
water body around the globe, including a wide range of extreme environments. Individual species, however, have
limited distributions and ecological requirements. Preservation of the glass cell walls in sedimentary basins has left
nearly a 120 million year record. Species-related distributions, and well-preserved record make diatoms an excellent tool
for environmental reconstruction and monitoring. New research on diatoms includes applications to conservation
biology, astrobiology, nanotechnology, and biofuels.
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Culturable bacteria have recently been found in the stratosphere (at heights up to 41km). How do such bacteria cross the
tropopause to reach such heights? Although possible mechanisms are suggested here, such transfer remains difficult to
explain. It is however, likely to more easily achieved by sub-micron bacteria. Such small forms have been found in
terrestrial environments and have the potential to seed the stratosphere. Large, ten micron clumps of bacteria have also
been found in the stratosphere and it is suggested that these are incoming to Earth from space. Finally, the possibility
will be discussed that the presence of bacteria in the stratosphere has led to an increase in the rate of evolution.
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Early life on Earth had to cope with harsh conditions, including full spectrum solar UV. Since DNA absorbs in the highly
energetic UV-C and VUV, solar irradiation was likely an obstacle to the expansion of life on Earth, until biological
mechanisms evolved to cope with UV liability (including the biosynthesis of UV screens) and ozone (derived from
oxygen produced by photosynthesis) accumulated in the stratosphere. In an effort to better understand the UV liability of
DNA, we used synchrotron light to measure VUV-UV absorption spectra (125-340 nm) for DNA and its components
(oligonucleotides and mononucleotides). We also measured VUV-UV absorption spectra for potential and known UV
screens, including amino acids, proteins, amines (including polyamines), scytonemin, mycosporine-like amino acids, β-
carotene, melanin and flavonoids. Among these, flavonoids seem remarkably suited to protecting DNA in the VUV-UV.
Flavonoids accumulate in seed coats, where they confer resistance to monochromatic UV (254 nm) and polychromatic
UV (200-400 nm). We discuss these findings in relation to the origin and evolution of life and its potential dispersal
through space.
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The worldwide effort to grow nanotechnology, rather than use lithography, focuses on diatoms, single cell eukaryotic
algae with ornate silica shells, which can be replaced by oxides and ceramics, or reduced to elemental silicon, to create
complex nanostructures with compositions of industrial and electronics importance. Diatoms produce an enormous
variety of structures, some of which are microtubule dependent and perhaps sensitive to microgravity. The NASA
Single Loop for Cell Culture (SLCC) for culturing and observing microorganisms permits inexpensive, low labor in-space
experiments. We propose to send up to the International Space Station diatom cultures of the three diatom species
whose genomes are currently being sequenced, plus the giant diatoms of Antarctica (up to 6 mm length for a single cell)
and the unique colonial diatom, Bacillaria paradoxa. Bacillaria cells move against each other in partial synchrony, like
a sliding deck of cards, by a microfluidics mechanism. Will normal diatoms have aberrant patterns, shapes or motility
compared to ground controls? The generation time is typically one day, so that many generations may be examined
from one flight. Rapid, directed evolution may be possible running the SLCC as a compustat. The shell shapes and
patterns are preserved in hard silica, so that the progress of normal and aberrant morphogenesis may be followed by
drying samples on a moving filter paper "diatom tape recorder". With a biodiversity of 100,000 distinct species, diatom
nanotechnology may offer a compact and portable nanotechnology toolkit for space exploration anywhere.
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Microorganisms occupy almost every habitable niche on Earth. Some of them may use inorganic or
organic substances rather than light as energy sources. We refer to this group as chemotrophs in order
to distinguish them from those organisms that use light as an energy source (phototrophs). Both
chemotrophs and phototrophs are abundant in environments where one or more physical, or chemical
parameters show values far from the lower or upper limits known for life. These ambient habitats are
referred to as normal environments. When microorganisms succeed in adapting themselves to harsh
niches they are referred to collectively as extremophiles (Seckbach 2004, 2006).
We review arguments that militate in favor of microorganisms that in the past and present may have
occupied other niches in the Solar System. Among the extremophiles we find representatives of the
three domains of life (Bacteria, Archaea, and Eukarya). Some of the possible candidates for life in the
Solar System are the extremophiles including chemotrophs, especially sulfur-reducing bacteria (SRB).
Another example of chemotrophs are the methanogens. Those microbes are capable of producing
methane as a metabolic byproduct of the reduction of carbon dioxide, a process that is called
methanogenesis. Searching for new forms of life (within the extraterrestrial regions) is the object of
planning within the Cosmic Vision Program of ESA, in collaboration with NASA, and other space
agencies. Indeed, sulfur traces on Jupiter's moon Europa detected by the Galileo mission have been
conjectured to be endogenic, most likely of cryovolcanic origin, due to their non-uniform distribution
in patches. The Galileo space probe first detected the sulfur compounds, as well as revealing that this
moon almost certainly has a volcanically heated and potentially habitable ocean hiding beneath Europa
surface layer of icy water. In this paper we restrict our attention to possible biomarkers that could
signal on Europa the presence extremophiles in general and chemotrophs, especially the presence of
sulfur reducers.
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Compared to prevalent alkaline to neutral hypersaline environments, acidic hypersaline environments have been scarcely
studied. However, they hold interest to many researchers in that these environments have similar geological and
geochemical characteristics as those found in lithified strata on Mars. Fieldwork indicated that Lake Brown, located in
Western Australia, possessed pH values of 3.1-4.5 and salinity between 13.0-23.0%. Water column, groundwater, and
sediment samples were collected from the lake during the austral winter of 2005. These samples were analyzed with
both traditional culture and molecular methods. Modified growth media and minimal media were designed to match the
composition (Cl, Na, Mg, SO4, K, Ca, and Br) of Lake Brown surface and ground waters for the enrichment of
microorganisms. One of the isolates obtained, Brown 1, can grow in media that possesses pH values of 3-7 with optimal
growth at pH 4, salinity that ranged from 5% to saturation with optimal growth at 5% and could grow under
temperatures that ranged from 20°C to 65°C with optimal grow occurring at 37°C. The isolate's optimum growth
conditions are similar to those found in Lake Brown. The isolate is a Gram-negative rod that forms yellow colonies on
17% Phytogel. Its 16S rRNA gene can be amplified with bacterial primers but not with archaeal primers. Its 16S rRNA
gene sequence suggests that the isolate is a gamma proteobacterium. Studies on organisms isolated from environments
such as Lake Brown, an acid hypersaline lake, can provide an opportunity to both expand our knowledge of terrestrial
extremophiles and gain insight on the possible forms of life that might have existed on Mars.
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Soap Lake is a hypersaline, alkaline lake in Central Washington State (USA). For the past five years the lake has been
the site of an NSF Microbial Observatory project devoted to identifying critical geochemical and microbial
characteristics of the monimolimnion sediment and water column, and has demonstrated rich multispecies communities
occupy all areas of the lake. Soap Lake and similar soda lakes are subject to repeated transient periods of extreme
evaporation characterized by significant repetitive alterations in salinity, pH, and total water volume, yet maintain high
genetic and metabolic diversity. It has been argued that this repetitive cycle for salinity, alkalinity, and sulfur
concentration has been a major driver for prokaryote evolution and diversity. The rapidity of wet-dry cycling places
special demands on genome evolution, requirements that are beyond the relatively conservative eukaryotic evolutionary
strategy of serial alteration of existing gene sequences in a relatively stable genome. Although HGT is most likely
responsible for adding a significant amount of noise to the genetic record, analysis of HGT activity can also provide us
with a much-needed probe for exploration of prokaryotic genome evolution and the origin of diversity. Packaging of
genetic information within the protective protein capsid of a bacteriophage would seem preferable to exposing naked
DNA to the highly alkaline conditions in the lake. In this study, we present preliminary data demonstrating the presence
of a diverse group of phage integrases in Soap Lake. Integrase is the viral enzyme responsible for the insertion of phage
DNA into the bacterial host's chromosome. The presence of the integrase sequence in bacterial chromosomes is evidence
of lysogeny, and the diversity of integrase sequences reported here suggests a wide variety of temperate phage exist in
this system, and are especially active in transition zones.
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The High-Lakes Project is funded by the NAI and explores the highest perennial volcanic lakes on Earth in the Bolivian
and Chilean Andes, including several lakes ~6,000 m elevation. These lakes represent an opportunity to study the
evolution of microbial organisms in relatively shallow waters not providing substantial protection against UV radiation.
Aguas Calientes (5,870 m) was investigated (November 2006) and samples of water and sediment collected at 1, 3, 5,
and 10 cm depth. An Eldonet UV dosimeter positioned on the shore records UV radiation and temperature, and is
logging data year round. A UV SolarLight sensor allowed acquisition of point measurements in all channels at the time
of the sampling. UVA, UVB, and PAR peaks between 11:00 am and 1:00 pm reached 7.7 mW/cm2, 48.5 μW/cm2, and
511 W/m2, respectively. The chemical composition of the water sample was analyzed. DNA was extracted and DGGE
analyses with bacterial and archaeal 16S fragments were performed to describe microbial diversity. Antibiotic
resistances were established previously in similar environments in Argentine Andean wetlands. In order to determine
these resistances in our samples, they were inoculated onto LB and R2A media and onto R2A medium containing either
chloramphenicol, ampicillin or tetracycline. Bacterial was higher than archeal cell number determined by RT-PCR in all
the samples, reaching maximum total values of 5x105 cell mL-1. DGGE results from these samples and Licancabur
summit lake (5,916 m) samples were also compared. Eight antibiotic-resistant Gram negative strains have been isolated
with distinct resistance patterns.
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The impact of individual extremes on life, such as UV radiation (UVR), temperatures, and salinity is well
documented. However, their combined effect in nature is not well-understood while it is a fundamental issue controlling
the evolution of habitat sustainability within individual bodies of water. Environmental variables combine in the
Bolivian Altiplano to produce some of the highest, least explored and most poorly understood lakes on Earth. Their
physical environment of thin atmosphere, high ultraviolet radiation, high daily temperature amplitude, ice, sulfur-rich
volcanism, and hydrothermal springs, combined with the changing climate in the Andes and the rapid loss of aqueous
habitat provide parallels to ancient Martian lakes at the Noachian/Hesperian transition 3.7-3.5 Ga ago. Documenting this
analogy is one of the focuses of the High-Lakes Project (HLP). The geophysical data we collected on three of them
located up to 5,916 m elevation suggests that a combination of extreme factors does not necessarily translate into a
harsher environment for life. Large and diverse ecosystems adapt to UVR reaching 200%-216% that of sea level in
bodies of water sometimes no deeper than 50 cm, massive seasonal freeze-over, and unpredictable daily evolution of
UVR and temperature. The HLP project has undertaken the first complete geophysical and biological characterization of
these lakes and documents how habitability is sustained and prolonged in declining lakes despite a highly dynamical
environment. The same process may have helped life transition through climate crises over time on both Earth and Mars.
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Recent developments in nanopore analysis of macromolecules and liquid-core optical waveguides have the potential to
allow fabrication of fully planar optofluidic labs-on-a-chip. Nanopores are able to detect single molecules of
biopolymers such as DNA and proteins, and liquid-core antiresonant reflecting optical (ARROW) waveguides also have
this capability. We are developing an instrument that combines the strengths of both approaches which we believe will
lead to a high-performance, low-cost instrument suitable for life detection on planetary surfaces such as Mars and
Europa.
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Last year at this meeting we described a computer application (Brown and Storrie-Lombardi, 2006),
the Mars Reconnaissance PRISM or MR PRISM, designed to analyze hyperspectral data collected
by the Compact Imaging Spectrometer for Mars (CRISM). The application links the spectral,
imaging and mapping perspectives on the CRISM dataset by presenting the user with three different
ways to analyze the data. At this time last year, CRISM was still in calibration mode and we
presented data from ESA's OMEGA instrument to demonstrate the functionality of MR CRISM.
A primary goal in developing this application is to make the latest algorithms for detection of
spectrally interesting targets available to the Planetary Science community without cost to the
individual investigator and with a minimal learning barrier. This would enable the community to
look for Mars surface targets such as ices, hydrothermal minerals, sulfate minerals and hydrous
minerals and map the extent of these deposits. The CRISM team has now provided significant data
sets to our community. We have used one such data set to conduct a study on an exposed water ice
mound. We review here our results on observations made of a ~36km diameter crater, recently
named Louth, in the north polar region of Mars (at 70°N, 103.2°E). High-resolution imagery from
the instruments on the Mars Reconnaissance Orbiter spacecraft were used to map a 15km diameter
water ice deposit in the center of the crater. The water ice mound has surface features that include
roughened ice textures and layering similar to that found in the North Polar Layered Deposits. We
describe the data analysis process including detection and mapping of hydroxyl mineral signatures
using the MR PRISM software suite.
MR PRISM is currently in the prototyping stage. Future additions planned include a Bayesian
analysis engine, the capacity to handle atmospheric correction routines provided by the CRISM
team, the ability to display MOC, THEMIS and HiRISE data and eventually the ability to run on a
distributed network to speed up processing of large image cubes. When the software is released to
the general community, we hope its embedded scripting language, 'Groovy', will make it the 'front
end' for many more sophisticated algorithms from all branches of Mars research.
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We developed a high resolution light imaging system. Diffraction gratings with 100 nm width lines as well as less than
100 nm size features of different-shaped objects are clearly visible on a calibrated microscope test slide (Vainrub et al.,
Optics Letters, 2006, 31, 2855). The two-point resolution increase results from a known narrowing of the central
diffraction peak for the annular aperture. Better visibility and advanced contrast of the smallest features in the image are
due to enhancement of high spatial frequencies in the optical transfer function. The imaging system is portable, low
energy, and battery operated. It has been adapted to use in both transmitting and reflecting light. It is particularly
applicable for motile nanoform systems where structure and functions can be depicted in real time. We have isolated
micrometer and submicrometer particles, termed proteons, from human and animal blood. Proteons form by reversible
seeded aggregation of proteins around proteon nucleating centers (PNCs). PNCs are comprised of 1-2nm metallic
nanoclusters containing 40-300 atoms. Proteons are capable of spontaneous assembling into higher nanoform systems
assuming structure of complicated topology. The arrangement of complex proteon system mimics the structure of a
small biological cell. It has structures that imitate membrane and nucleolus or nuclei. Some of these nanoforms are
motile. They interact and divide. Complex nanoform systems can spontaneously reduce to simple proteons. The
physical properties of these nanoforms could shed some light on the properties of early life forms or forms at extreme
conditions.
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To settle an optimal analytical strategy of the search for life traces, it is decisive to start their study in the preliminary
examination stages of the extraterrestrial Returned Samples, once they are still stored in their original container. The
relevance of the application of on-going synchrotron micro-X-ray fluorescence (XRF) methodological developments
performed at the ID21/ID22 beamlines of the ESRF is critically examined in this paper. XRF computed tomography
(CT) at ID22 is in general a precious tool allowing a non-invasive and non-destructive determination of the three-dimensional
mineralogy with micrometer resolution of sub-millimeter silicate grains. A combination of absorption and
Compton tomographies is a more promising method to image bulk views of the organic matter distribution. XRF-scanning
X-ray microscopy (SXM) at ID21 is in general not adapted for studying samples across a container. However, it
appears to be a unique tool to draw up a list of the sub-surface sites where tiny amounts of organic matter are present.
Adaptation of the SXM chamber to the quarantine criteria stipulated by the spatial agencies is a way to permit such
analyses in the preliminary examination stages.
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Survivability to Radiation, Dessication, and Shock
Great Salt Lake (GSL) is home to halophiles, salt-tolerant Bacteria and Archaea, which live at 2-5M NaCl. In addition
to salt tolerance, GSL halophiles exhibit resistance to both ultraviolet (UV) irradiation and desiccation. First, to
understand desiccation resistance, we sought to determine the diversity of GSL halophiles capable of surviving
desiccation in either recently formed GSL halite crystals or GSL Artemia (brine shrimp) cysts. From these desiccated
environments, surviving microorganisms were cultured and isolated, and genomic DNA was extracted from the
individual species for identification by 16S rRNA gene homology. From the surface-sterilized cysts we also extracted
DNA of the whole microbial population for non-cultivation techniques. We amplified the archaeal or bacterial 16S
rRNA gene from all genomic DNA, cloned the cyst population amplicons, and sequenced. These sequences were
compared to gene databases for determination of closest matched species. Interestingly, the isolates from the crystal
dissolution are distinct from those previously isolated from GSL brine. The cyst population results reveal species not
found in crystals or brine, and may indicate microorganisms that live as endosymbionts of this hypersaline arthropod.
Second, we explored UV resistance in a GSL haloarchaea species, "H. salsolis." This strain resists UV irradiation an
order of magnitude better than control species, all of which have intact repair systems. To test the hypothesis that
halophiles have a photoprotection system, which prevents DNA damage from occurring, we designed an immunoassay
to detect thymine dimers following UV irradiation. "H. salsolis" showed remarkable resistance to dimer formation.
Evidence for both UV and desiccation resistance in these salt-tolerant GSL halophiles makes them well-suited as models
for Astrobiological studies in pursuit of questions about life beyond earth.
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An analysis is carried out of the survival fraction of micro-organisms exposed to extreme shock pressures. A variety of
data sources are used in this analysis. The key findings are that survival depends on the behaviour of the cell wall. Below
a critical shock pressure there is a relatively slow fall in survival fraction as shock pressures increase. Above the critical
threshold survival starts to fall rapidly as shock pressure increases further. The critical shock pressures found here are in
the range 2.4 to 20 GPa, and vary not only from organism to organism, but also depend on the growth stage of given
organisms, with starved (i.e., no growth) states favoured for survival. At the shock pressures typical of those involved in
interplanetary transfer of rocky materials, the survival fractions are found to be small but finite. This lends credence to
the idea of Panspermia, i.e. life may naturally migrate through space. Thus for example, Martian meteorites should not a
prior be considered as sterile due to the shock processes they have undergone, but their lack of viable micro-organisms
either reflects no such life being present at the source at the time of departure or the influence of other hazardous
processes such as radiation in space or heating of surfaces during entry into a planetary atmosphere.
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The radiation resistance-repair genes in Deinococcus radiodurans (DR) and E-coli were analyzed in terms of the
A, T, C, G nucleotide fluctuations. The studied genes were Rec-A, Rec-Q, and the unique DR PprA gene. In an
ATCG sequence, each base was assigned a number equal to its atomic number. The resulting numerical
sequence was the basis of the statistical analysis. Fractal analysis using the Higuchi method gave a fractal
dimension increase of the Deinococcus radiodurans genes as compared to E-coli, which is comparable to the
enhancement observed in the human HAR1 region (HAR1F gene) over that of the chimpanzee. Near neighbor
fluctuation was also studied via the Black-Scholes model where the increment sequence was treated as a random
walk series. The Deinococcus radiodurans radiation gene standard deviations were consistently higher than that
of the E-coli deviations, and agree with the fractal analysis results. The sequence stacking interaction was
studied using the published nucleotide-pair melting free energy values and Deinococcus radiodurans radiation
genes were shown to possess larger negative free energies. The high sensitivity of the fractal dimension as a
biomarker was tested with correlation analysis of the gamma ray dose versus fractal dimension, and the R square
values were found to be above 0.9 (N=5). When compared with other nucleotide sequences such as the rRNA
sequences, HAR1 and its chimpanzee counterpart, the higher fluctuation (correlated randomness) and larger
negative free energy of a DR radiation gene suggested that a radiation resistance-repair sequence exhibited
higher complexity. As the HAR1 nucleotide sequence complexity and its transcription activity of co-expressing
cortex protein reelin supported a positive selection event in humans, a similar inference of positive selection of
coding genes could be drawn for Deinococcus radiodurans when compared to E-coli. The origin of such a
positive selection would be consistent with that of a Martian environment.
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The surface of Mars is exposed to higher levels of solar and galactic cosmic ray irradiation than Earth due to its
very weak magnetic field. Thus, microorganisms that could possibly survive in the shallow subsurface of Mars would
likely be radiotolerant. To better understand microorganisms that might reside in this environment of Mars, a number of
isolates were obtained from the area around a gamma-radiation source, 137Cs, located on the UMR campus. Radiation
sensitivity assays were performed on the isolates as well as on the common bacterium, E. coli. All the organisms tested
were able to withstand exposures up to 20 Gy. The E. coli control did not survive exposures of 200 Gy, while the isolate
designated 1B-1 could. Another isolate, Cont-1, also withstood this exposure. Each of the isolates produced white
growth on solid medium and their cells are rod-shaped. The study of these isolates and similar organisms could enhance
our knowledge of these unique extremophilic bacteria and might provide insight into the microorganisms that could be
present in the shallow subsurface of Mars.
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Chirality is an excellent indicator of life, but naturally occurring terrestrial and extra-terrestrial
samples nearly always exhibit massive depolarizing light scattering (DLS). This problem bears a
striking resemblance to that of developing a chirality-based non-invasive glucose monitor for diabetics.
Both applications require a lightweight, compact, efficient, and robust polarimeter that can operate
despite significant DLS. So for astrobiological applications, we developed a polarimeter that was
inspired from a polarimetry technique previously investigated for non-invasive in-vivo glucose-sensing.
Our polarimeter involves continuously rotating the plane of linear polarization of a laser beam to probe
a sample with DLS, and analyzing its transmission with a fixed analyzer to obtain a sinusoidal voltage
signal. We lock-in detect this signal using a reference signal from an analogous set up without any
sample. With milk as a scatterer, we find that this polarimeter detects chirality in the presence of three
orders of magnitude more DLS than conventional polarimeters. It can accurately measure 0.1° of
polarization rotation in the presence of 15% milk.
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Often, micromorphologies, interpreted as microfossils, provide the first clues to exciting and potentially
controversial discoveries related to the early origins of life on the Earth, as well as the potential for life on other
planets. It has been said, however, that exceptional claims require exceptional proof, and micromorphological
evidence alone may have several possible interpretations, both biotic and abiotic. Garcia-Ruiz, et al. (2003) have
shown how silica-coated carbonate crystals in a chert-like matrix can self-assemble inorganically into long folded or
braided filaments that closely resemble cyanobacteria fossils thought to be 3.5 billion years old. Recent advances in
the field of Materials Science provide numerous other examples ofmicromorphologies that, due to their complexity
and structure, might be misinterpreted as microfossils despite their clearly abiotic origin. Several examples will be
discussed. While the chemistries ofthese abiotic micromorphologies could be considered rather exotic and therefore
discounted, the same fossilization process that operates on biotic microorganisms could operate here as well.
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The label "soil" is used in a great variety of significations but seldom to indicate what is meant by it as a thorough
concept in soil science/pedology. This is particularly true when used by scientists not acquainted with soil science even
on Earth. Hence, the label "soil" very often stands for features occurring in surficial deposits of planets (as the Earth
itself) not really dealing with soil development. Soil development is a complex result/product from major natural factors
as water/precipitation, geomorphology/edaphic position, sediment /surficial deposits and by and large climate. All these
factors are reflected in a "soil-type" of the earthly soil-classification-system. In reverse "soils" reflect pedologic/climatic
conditions of the past possibly pointing at the presence of water and vegetation in a given landscape. As soils are thus
intrinsically related to life on planets as on Earth the label soil in searching for Life on Mars should be used properly.
Phyllosilicates and red clays (even in traces) recently discovered by many scientists on the Red Planet may indicate the
presence of thorough soils on Mars. The term "regolith" for the Martian soil should then be avoided.
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The microflora of the cryosphere of planet Earth provides the best analogs for life forms that might be found in the
permafrost or polar ice caps of Mars, near the surface of the cometary nuclei, or in the liquid water beneath the ice
crusts of icy moons of Jupiter and Saturn. For astrobiology the focus on the study alkaliphilic microorganisms was
enhanced by the findings of abundant carbonates and carbonate globules rimmed with possibly biogenic magnetites in
association with the putative microfossils in the ALH84001 meteorite. Although the ALH84001 "nanofossils" were too
small and simple to be unambiguously recognized as biogenic, they stimulated Astrobiology research and studies of
microbial extremophiles and biomarkers in ancient rocks and meteorites. Recent studies of CI and CM carbonaceous
meteorites have resulted in the detection of the well-preserved mineralized remains of coccoidal and filamentous
microorganisms in cyanobacterial mats. Energy Dispersive X-ray Analysis has shown anomalous biogenic element
ratios clearly indicating they are not recent biological contaminants.
This paper reviews microbial extremophiles in context of their significance to Astrobiology and the evolution of
life. Extremophilic microorganisms on Earth are models for life that might endure high radiation environments in the
ice near the surface of comets or on the icy moons of Jupiter and Saturn and in the seafloor deep beneath the icy crusts
of Europa and Enceladus.
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We present design, integration and test results for a field Raman spectrometer science payload, integrated into the Mars
Analog Research and Technology (MARTE) drilling platform. During the drilling operation, the subsurface Raman
spectroscopy inspection system has obtained signatures of organic and mineral compositions. We also performed ground
truth studies using both this field unit and a laboratory micro Raman spectrometer equipped with multiple laser
excitation wavelengths on series of field samples including Mojave rocks, Laguna Verde salty sediment and Rio Tinto
topsoil. We have evaluated laser excitation conditions and optical probe designs for further improvement. We have
demonstrated promising potential for Raman spectroscopy as a non-destructive in situ, high throughput, subsurface
detection technique, as well as a desirable active remote sensing tool for future planetary and space missions.
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Rapid adaptation to acute environmental change demands co-evolution of indigenous viral populations and their hosts.
Horizontal gene transfer (HGT) is a highly efficient adaptive mechanism, but a difficult phenomena to dectect. The
mosaic nature of bacteriophage genomes resulting from HGT has generally been explored using phylogenetic analysis of
coding regions. Focusing on the proteome certainly provides one window into the origin and evolution of genome
information storage. However, the original fitness function for a nucleotide polymer would arise from a more primal
survival imperative predating the appearance of a coding function. Multivariate analysis of a genome information storage
metric (lossless compression), nucleotide distributions, and distributions of the three major physiochemical
characteristics of the polymer (triple:double bonding [G+C], purine:pyrimidine [G+A], and keto:amine [G+T] fractions)
produces a metric to detect and characterize mosaicism in both coding and non-coding regions of a genome. We discuss
possibilities and limitations of using these techniques to investigate HGT and the origins and evolution of genome
complexity. Analysis of available virus (n= 2374) and bacteriophage genomes (n=417) indicates these probes can
perform whole-genome taxonomy tasks or sliding window searches for evidence of HGT in a single genome. HGT
responses may serve as a canary or bell-weather for global environmental change. We discuss one area of application of
considerable interest to our institute: the response of cyanophage and their cyanobacteria hosts to variations in ultraviolet
solar flux in geographically isolated Antarctic lakes.
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In this paper we discuss the astrobiological importance of various viruses, nanobacteria, Archaea and bacteria. Viruses
and nanobacteria challenge the current definitions of life, but we consider them here as life forms. Nanobacteria have
interesting mode of fossilization and have a potential for creating biosignatures. Archaea and some bacteria make
unique lipid-related compounds that can be used as biosignatures. We focus on the organisms and life forms that seem to
be well suited for the life on Mars or other extraterrestrial environments that are harsh. Many of these organisms and life
forms share their genetic material freely with other organisms and species. Such an altruistic approach may have been
typical for the early life on Earth.
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The Maillard reaction occurs when sugars and amino acids are mixed together in the solid state or in the aqueous solution. Since both amino acids and sugar-like compounds are found on meteorites, we hypothesized that they would also undergo the Maillard reaction. Our recent work supports this idea. We have shown previously that the water-insoluble Maillard products have substantial similarities with the insoluble organic materials from the meteorites. The Maillard organic materials are also part of the desert varnish on Earth, which is a dark, shiny, hard rock coating that contains iron and manganese and is glazed in silicate. Rocks that are similar in appearance to the desert varnish have been observed on the Martian surface. They may also contain the organic materials. We have undertaken study of the interactions between the Maillard products, iron and other metals, and silicates, to elucidate the role of the Maillard products in the chemistry of desert varnish and meteorites. Specifically, we have synthesized a series of the Maillard-metal complexes, and have tested their reactivity towards silicates. We have studied the properties of these Maillard-metal-silicate products by the IR spectroscopy. The astrobiological potential of the Maillard-metal complexes is assessed.
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In the soft reduced sediments of the continental shelf, below the oxygen minimum zone (OMZ) of the eastern
South Pacific (ESP), peculiar microbial communities have been disclosed which include a variety of large prokaryotes,
protists and small metazoans. Dominant among the prokaryotes are large multi-cellular filamentous bacteria which,
according to their size range, are roughly divided into megabacteria and macrobacteria. The former group is made up of
a few species of Gamma Proteobacteria of the genera Thioploca and Beggiatoa and the second group includes a diversity
of phenotypes. Protists include ciliates, flagellates, and foraminifers and the metazoans are mostly nematodes and small
polychaetes. A significant similarity has been found in the exploitation of the area/volume relationship among these large
bacteria and their fossil analog forms as described from pre-Cambrian rocks. For the same reason, the latter have mostly
been referred to as algae or cyanobacteria in the literature. The presence of these seemingly ancient bacteria in the
sediments of the oxygen minimum zones of the ESP, one of the most productive but also ecologically most inefficient
marine ecosystems of the world, suggests that such setting must have prevailed throughout the geological history of the
planet allowing for their survival and further that it might be considered an analog of Proterozoic ocean conditions. These
non-cyanobacterial communities offer an alternative hypothesis to students of the evolution of life on Earth and may be
of special interest to astrobiologists looking for life or traces of life in terrestrial or extraterrestrial environments since
these do not necessarily imply a photosynthesis-based metabolism.
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