Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars.

The Sample Analysis at Mars instrument stepped combustion experiment on a Yellowknife Bay mudstone at Gale crater, Mars revealed the presence of organic carbon of Martian and meteoritic origins. The combustion experiment was designed to access refractory organic carbon in Mars surface sediments by heating samples in the presence of oxygen to combust carbon to CO2. Four steps were performed, two at low temperatures (less than ∼550 °C) and two at high temperatures (up to ∼870 °C). More than 950 µg C/g was released at low temperatures (with an isotopic composition of δ13C = +1.5 ± 3.8‰) representing a minimum of 431 µg C/g indigenous organic and inorganic Martian carbon components. Above 550 °C, 273 ± 30 µg C/g was evolved as CO2 and CO (with estimated δ13C = -32.9‰ to -10.1‰ for organic carbon). The source of high temperature organic carbon cannot be definitively confirmed by isotopic composition, which is consistent with macromolecular organic carbon of igneous origin, meteoritic infall, or diagenetically altered biomass, or a combination of these. If from allochthonous deposition, organic carbon could have supported both prebiotic organic chemistry and heterotrophic metabolism at Gale crater, Mars, at ∼3.5 Ga.

Increased MRI-based Brain Age in chronic migraine patients.

INTRODUCTION: Neuroimaging has revealed that migraine is linked to alterations in both the structure and function of the brain. However, the relationship of these changes with aging has not been studied in detail. Here we employ the Brain Age framework to analyze migraine, by building a machine-learning model that predicts age from neuroimaging data. We hypothesize that migraine patients will exhibit an increased Brain Age Gap (the difference between the predicted age and the chronological age) compared to healthy participants. METHODS: We trained a machine learning model to predict Brain Age from 2,771 T1-weighted magnetic resonance imaging scans of healthy subjects. The processing pipeline included the automatic segmentation of the images, the extraction of 1,479 imaging features (both morphological and intensity-based), harmonization, feature selection and training inside a 10-fold cross-validation scheme. Separate models based only on morphological and intensity features were also trained, and all the Brain Age models were later applied to a discovery cohort composed of 247 subjects, divided into healthy controls (HC, n=82), episodic migraine (EM, n=91), and chronic migraine patients (CM, n=74). RESULTS: CM patients showed an increased Brain Age Gap compared to HC (4.16 vs -0.56 years, P=0.01). A smaller Brain Age Gap was found for EM patients, not reaching statistical significance (1.21 vs -0.56 years, P=0.19). No associations were found between the Brain Age Gap and headache or migraine frequency, or duration of the disease. Brain imaging features that have previously been associated with migraine were among the main drivers of the differences in the predicted age. Also, the separate analysis using only morphological or intensity-based features revealed different patterns in the Brain Age biomarker in patients with migraine. CONCLUSION: The brain-predicted age has shown to be a sensitive biomarker of CM patients and can help reveal distinct aging patterns in migraine.

Synthetic MRI improves radiomics-based glioblastoma survival prediction.

Glioblastoma is an aggressive and fast-growing brain tumor with poor prognosis. Predicting the expected survival of patients with glioblastoma is a key task for efficient treatment and surgery planning. Survival predictions could be enhanced by means of a radiomic system. However, these systems demand high numbers of multicontrast images, the acquisitions of which are time consuming, giving rise to patient discomfort and low healthcare system efficiency. Synthetic MRI could favor deployment of radiomic systems in the clinic by allowing practitioners not only to reduce acquisition time, but also to retrospectively complete databases or to replace artifacted images. In this work we analyze the replacement of an actually acquired MR weighted image by a synthesized version to predict survival of glioblastoma patients with a radiomic system. Each synthesized version was realistically generated from two acquired images with a deep learning synthetic MRI approach based on a convolutional neural network. Specifically, two weighted images were considered for the replacement one at a time, a T2w and a FLAIR, which were synthesized from the pairs T1w and FLAIR, and T1w and T2w, respectively. Furthermore, a radiomic system for survival prediction, which can classify patients into two groups (survival >480 days and ≤ 480 days), was built. Results show that the radiomic system fed with the synthesized image achieves similar performance compared with using the acquired one, and better performance than a model that does not include this image. Hence, our results confirm that synthetic MRI does add to glioblastoma survival prediction within a radiomics-based approach.

Evidence for indigenous nitrogen in sedimentary and aeolian deposits from the Curiosity rover investigations at Gale crater, Mars.

The Sample Analysis at Mars (SAM) investigation on the Mars Science Laboratory (MSL) Curiosity rover has detected oxidized nitrogen-bearing compounds during pyrolysis of scooped aeolian sediments and drilled sedimentary deposits within Gale crater. Total N concentrations ranged from 20 to 250 nmol N per sample. After subtraction of known N sources in SAM, our results support the equivalent of 110-300 ppm of nitrate in the Rocknest (RN) aeolian samples, and 70-260 and 330-1,100 ppm nitrate in John Klein (JK) and Cumberland (CB) mudstone deposits, respectively. Discovery of indigenous martian nitrogen in Mars surface materials has important implications for habitability and, specifically, for the potential evolution of a nitrogen cycle at some point in martian history. The detection of nitrate in both wind-drifted fines (RN) and in mudstone (JK, CB) is likely a result of N2 fixation to nitrate generated by thermal shock from impact or volcanic plume lightning on ancient Mars. Fixed nitrogen could have facilitated the development of a primitive nitrogen cycle on the surface of ancient Mars, potentially providing a biochemically accessible source of nitrogen.

Isotopes of nitrogen on Mars: Atmospheric measurements by Curiosity's mass spectrometer.

[1] The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) measured a Mars atmospheric14N/15N ratio of 173 ± 11 on sol 341 of the mission, agreeing with Viking's measurement of 168 ± 17. The MSL/SAM value was based on Quadrupole Mass Spectrometer measurements of an enriched atmospheric sample, with CO2 and H2O removed. Doubly ionized nitrogen data at m/z 14 and 14.5 had the highest signal/background ratio, with results confirmed by m/z 28 and 29 data. Gases in SNC meteorite glasses have been interpreted as mixtures containing a Martian atmospheric component, based partly on distinctive14N/15N and40Ar/14N ratios. Recent MSL/SAM measurements of the40Ar/14N ratio (0.51 ± 0.01) are incompatible with the Viking ratio (0.35 ± 0.08). The meteorite mixing line is more consistent with the atmospheric composition measured by Viking than by MSL.

Thermal Stability of (Bio)Carbonates: A Potential Signature for Detecting Life on Mars?

The environmental conditions that prevail on the surface of Mars (i.e., high levels of radiation and oxidants) are not favorable for the long-term preservation of organic compounds on which all strategies for finding life on Mars have been based to date. Since life commonly produces minerals that are considered more resilient, the search for biominerals could constitute a promising alternative approach. Carbonates are major biominerals on Earth, and although they have not been detected in large amounts at the martian surface, recent observations show that they could constitute a significant part of the inorganic component in the martian soil. Previous studies have shown that calcite and aragonite produced by eukaryotes thermally decompose at temperatures 15°C lower than those of their abiotic counterparts. By using carbonate concretions formed by microorganisms, we find that natural and experimental carbonates produced by prokaryotes decompose at 28°C below their abiotic counterparts. The study of this sample set serves as a proof of concept for the differential thermal analysis approach to distinguish abiotic from bio-related carbonates. This difference in carbonate decomposition temperature can be used as a first physical evidence of life on Mars to be searched by in situ space exploration missions with the resolution and the technical constraints of the available onboard instruments.

Optimizing Chiral Selectivity in Practical Life-Detection Instruments.

Preferential uptake of either levorotatory (L) or dextrorotatory (D) enantiomer of a chiral molecule is a potential planetary life-detection method. On Earth, bacteria, as a rule, metabolize D-sugars and L-amino acids. Here, we use growth experiments to identify exceptions to the rule and their potential impact on the method's reliability. Our experiments involve six strains of Bacillus and collective uptake of the sugars glucose and arabinose, and the amino acids alanine, glutamic acid, leucine, cysteine, and serine-all of which are highly soluble. We find that selective uptake is not evident unless (1) each sugar is tested individually and (2) multiple amino acids are tested together in a mixture. Combining sugars should be avoided because, as we show in Bacillus bacteria, the same organisms may catabolize one sugar, glucose, in D-form and another sugar, arabinose, in L-form. Single amino acids should be avoided because bacteria can access certain proteinogenically incompatible enantiomers using specific racemases. Specifically, bacteria contain an alanine acid racemase and can catabolize D-alanine if no other D-amino acids are present. The proposed improvements would reliably separate nonselective chemical reactions from biological reactions and, if life is indicated, inform whether the selective patterns for amino acids and sugars are the same as on Earth.

Radiolytic Degradation of Soil Carbon from the Mojave Desert by 60Co Gamma Rays: Implications for the Survival of Martian Organic Compounds Due to Cosmic Radiation.

The martian surface has been continuously exposed to galactic cosmic radiation. Since organic compounds are degraded by ionizing radiation, knowledge of their decay constants is fundamental to predicting their stability on the martian surface. In this study, we report the radiolysis constant for the destruction of soil organic compounds at a starting concentration of ∼2011 µg C/gsoil from the Mojave Desert. The soils were exposed to gamma irradiation with absorbed doses of up to 19 MGy at room temperature, representing ∼250 million years of exposure to galactic cosmic rays. The destruction of total soil organic carbon and the formation of gases were investigated by a sequential on-line analytical array coupled to gas chromatography-mass spectrometry. Soil inorganic and organic carbon were degraded exponentially with a radiolysis constant 0.3 MGy-1(30%) producing mostly carbon dioxide (93.2%), carbon monoxide (6.2%), and methane (0.6%). Using the dose rate measured by the Radiation Assessment Detector on board the Curiosity rover, we make predictions on the survival of organic compounds in the cold martian subsurface. It is estimated that soil organic compounds with initial concentrations as those found today at the Mojave Desert would have been destroyed to levels <1 ppb at 0.1 m in depth in ∼2000 Myr. Pristine organic compounds are expected to be present at a depth of ∼1.5 m. These results are relevant for the search of organic compounds in past, present, and future missions to Mars. In particular, we predict that the upcoming ExoMars will encounter pristine organic compounds at this depth.

Influence of Calcium Perchlorate on the Search for Martian Organic Compounds with MTBSTFA/DMF Derivatization.

N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA), mixed with the solvent N,N-dimethylformamide (DMF), is used as a derivatizing reagent by the Sample Analysis at Mars (SAM) experiment onboard NASA's Curiosity rover and will soon be utilized by the Mars Organic Molecule Analyzer experiment onboard the ESA/Roscosmos Rosalind Franklin rover. The pyrolysis products of MTBSTFA, DMF, and the MTBSTFA/DMF mixtures, obtained at different temperatures, were analyzed. Two different pyrolysis modes were studied, flash pyrolysis and ramp pyrolysis (35°C/min), to evaluate the potential influence of the sample heating speed on the production of products in space chromatographs. The effect of the presence of calcium perchlorate on the pyrolysis products of MTBSTFA/DMF was also studied to ascertain the potential effect of perchlorate species known to be present at the martian surface. The results show that MTBSTFA/DMF derivatization should be applied below 300°C when using flash pyrolysis, as numerous products of MTBSTFA/DMF were formed at high pyrolysis temperatures. However, when an SAM-like ramp pyrolysis was applied, the final pyrolysis temperature did not appear to influence the degradation products of MTBSTFA/DMF. All products of MTBSTFA/DMF pyrolysis are listed in this article, providing a major database of products for the analysis of martian analog samples, meteorites, and the in situ analysis of martian rocks and soils. In addition, the presence of calcium perchlorate does not show any obvious effects on the pyrolysis of MTBSTFA/DMF: Only chloromethane and TBDMS-Cl (chloro-tertbutyldimethylsilane) were detected, whereas chlorobenzene and other chlorine-bearing compounds were not detected. However, other chlorine-bearing compounds were detected after pyrolysis of the Murchison meteorite in the presence of calcium perchlorate. This result reinforces previous suggestions that chloride-bearing compounds could be reaction products of martian samples and perchlorate.

Influence of Calcium Perchlorate on the Search for Organics on Mars with Tetramethylammonium Hydroxide Thermochemolysis.

The Mars Organic Molecule Analyzer (MOMA) and Sample Analysis at Mars (SAM) instruments onboard the Exomars 2022 and Mars Science Laboratory rovers, respectively, are capable of organic matter detection and differentiating potentially biogenic from abiotic organics in martian samples. To identify organics, both these instruments utilize pyrolysis-gas chromatography coupled to mass spectrometry, and the thermochemolysis agent tetramethylammonium hydroxide (TMAH) is also used to increase organic volatility. However, the reactivity and efficiency of TMAH thermochemolysis are affected by the presence of calcium perchlorate on the martian surface. In this study, we determined the products of TMAH pyrolysis in the presence and absence of calcium perchlorate at different heating rates (flash pyrolysis and SAM-like ramp pyrolysis with a 35°C·min-1 heating rate). The decomposition mechanism of TMAH pyrolysis in the presence of calcium perchlorate was studied by using stepped pyrolysis. Moreover, the effect of calcium perchlorate (at Mars-relevant concentrations) on the recovery rate of fatty acids with TMAH thermochemolysis was studied. Results demonstrate that flash pyrolysis yields more diversity and greater abundances of TMAH thermochemolysis products than does the SAM-like ramp pyrolysis method. There is no obvious effect of calcium perchlorate on TMAH degradation when the [ClO4-] is lower than 10 weight percent (wt %). Most importantly, the presence of calcium perchlorate does not significantly impact the recovery rate of fatty acids with TMAH thermochemolysis under laboratory conditions, which is promising for the detection of fatty acids via TMAH thermochemolysis with the SAM and MOMA instruments on Mars.

First Detections of Dichlorobenzene Isomers and Trichloromethylpropane from Organic Matter Indigenous to Mars Mudstone in Gale Crater, Mars: Results from the Sample Analysis at Mars Instrument Onboard the Curiosity Rover.

Chromatographic analysis of the Cumberland mudstone in Gale crater by the Sample Analysis at Mars (SAM) instrument revealed the detection of two to three isomers of dichlorobenzene. Their individual concentrations were estimated to be in the 0.5-17 ppbw range relative to the sample mass. We also report the first detection of trichloromethylpropane and the confirmation of the detection of chlorobenzene previously reported. Supporting laboratory experiments excluded the SAM internal background as the source of those compounds, thus confirming the organic carbon and chlorine of the newly detected chlorohydrocarbons are indigenous to the mudstone sample. Laboratory experiments also demonstrated that the chlorohydrocarbons were mainly produced from chemical reactions occurring in the SAM ovens between organic molecules and oxychlorines contained in the sample. The results we obtained show that meteoritic organics and tested chemical species (a polycyclic aromatic hydrocarbon, an amino acid, and a carboxylic acid) were plausible organic precursors of the chlorinated aromatic molecules detected with SAM, thus suggesting that they could be among the organic molecules present in the mudstone. Results from this study coupled with previously reported detections of chlorinated aromatics (<300 ppbw) indigenous to the same mudstone highlight that organics can be preserved from the harsh surface conditions even at shallow depth. The detection of new chlorohydrocarbons with SAM confirms that organic molecules should have been available in an environment favorable to life forms, strengthening the habitability aspect of Gale crater.

Production of nitrates and perchlorates by laser ablation of sodium chloride in simulated Martian atmospheres. Implications for their formation by electric discharges in dust devils.

Nitrates and perchlorates are present both on Earth and Mars. In the Martian environment perchlorates dominate over nitrates whereas on Earth is contrariwise. This implies that the mechanisms responsible for their formation are different for both planets. The chemical elements required for their formation are nitrogen and chlorine, which are present in the atmosphere and surface, respectively. Dust in the Martian atmosphere causes atmospheric perturbations that lead to the development of dust-devils and sandstorms. Dust devils contain both chemical elements simultaneously, and normally generate high electric fields that can trigger the formation of electric discharges. Here we present laboratory experiments of this phenomenon using laser ablation of a sodium chloride (NaCl) plate in two different simulated atmospheres: (1) 96% CO2, 2% N2 and 2% Ar; and (2) 66% CO2, 33% N2 and 1% Ar. The dust that condensed and accumulated on the walls of the reactor was analyzed by different analytical techniques that included Fourier transform infrared spectroscopy, visible spectroscopy using azo dyes, thermogravimetry/simultaneous thermal analyses coupled to mass spectrometry, powder X-ray diffraction, and ion chromatography. The main components of the ablated dust corresponded to NaCl ≥ 91.5%, sodium nitrate (NaNO3 = 1.6-6.0%), and sodium perchlorate (NaClO4 âˆ¼ 0.2-0.3%). It is interesting to note that these salts formed in a dry process that is relevant to Mars today. A thermochemical model was used to understand the chemical steps that led to the formation of these salts in the gas phase. The NaNO3NaClO4 (wt/wt) ratio of this process was estimated to vary from 5.0 to 30.0; this ratio is too high compared to that found on Mars (NO3-ClO4- (wt/wt)) from 0.004 to 0.13). This implies that gaseous NaCl was not efficiently oxidized to perchlorate by the electric discharge process. We propose instead that gaseous metal chlorides (e.g., MgCl2, NaCl, CaCl2, KCl) were supplied to the atmosphere by the volatilization of chloride minerals present in the dust by electric discharges generated in dust devils and were subsequently oxidized to perchlorate by photochemical processes. Further work is required to assess the relative contribution of this possible source.

Recovery of Fatty Acids from Mineralogic Mars Analogs by TMAH Thermochemolysis for the Sample Analysis at Mars Wet Chemistry Experiment on the Curiosity Rover.

The Mars Curiosity rover carries a diverse instrument payload to characterize habitable environments in the sedimentary layers of Aeolis Mons. One of these instruments is Sample Analysis at Mars (SAM), which contains a mass spectrometer that is capable of detecting organic compounds via pyrolysis gas chromatography mass spectrometry (py-GC-MS). To identify polar organic molecules, the SAM instrument carries the thermochemolysis reagent tetramethylammonium hydroxide (TMAH) in methanol (hereafter referred to as TMAH). TMAH can liberate fatty acids bound in macromolecules or chemically bound monomers associated with mineral phases and make these organics detectable via gas chromatography mass spectrometry (GC-MS) by methylation. Fatty acids, a type of carboxylic acid that contains a carboxyl functional group, are of particular interest given their presence in both biotic and abiotic materials. This work represents the first analyses of a suite of Mars-analog samples using the TMAH experiment under select SAM-like conditions. Samples analyzed include iron oxyhydroxides and iron oxyhydroxysulfates, a mixture of iron oxides/oxyhydroxides and clays, iron sulfide, siliceous sinter, carbonates, and shale. The TMAH experiments produced detectable signals under SAM-like pyrolysis conditions when organics were present either at high concentrations or in geologically modern systems. Although only a few analog samples exhibited a high abundance and variety of fatty acid methyl esters (FAMEs), FAMEs were detected in the majority of analog samples tested. When utilized, the TMAH thermochemolysis experiment on SAM could be an opportunity to detect organic molecules bound in macromolecules on Mars. The detection of a FAME profile is of great astrobiological interest, as it could provide information regarding the source of martian organic material detected by SAM.

Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars.

Establishing the presence and state of organic matter, including its possible biosignatures, in martian materials has been an elusive quest, despite limited reports of the existence of organic matter on Mars. We report the in situ detection of organic matter preserved in lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds released at high temperatures (500° to 820°C), were directly detected by evolved gas analysis. Thiophenes were also observed by gas chromatography-mass spectrometry. Their presence suggests that sulfurization aided organic matter preservation. At least 50 nanomoles of organic carbon persists, probably as macromolecules containing 5% carbon as organic sulfur molecules.

Background levels of methane in Mars' atmosphere show strong seasonal variations.

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

Chemical and Biological Sensing Using Diatom Photonic Crystal Biosilica With In-Situ Growth Plasmonic Nanoparticles.

In this paper, we described a new type of bioenabled nano-plasmonic sensors based on diatom photonic crystal biosilica with in-situ growth silver nanoparticles and demonstrated label-free chemical and biological sensing based on surface-enhanced Raman scattering (SERs) from complex samples. Diatoms are photosynthetic marine micro-organisms that create their own skeletal shells of hydrated amorphous silica, called frustules, which possess photonic crystal-like hierarchical micro- & nanoscale periodic pores. Our research shows that such hybrid plasmonic-biosilica nanostructures formed by cost-effective and eco-friendly bottom-up processes can achieve ultra-high limit of detection for medical applications, food sensing, water/air quality monitoring and geological/space research. The enhanced sensitivity comes from the optical coupling of the guided-mode resonance of the diatom frustules and the localized surface plasmons of the silver nanoparticles. Additionally, the nanoporous, ultra-hydrophilic diatom biosilica with large surface-to-volume ratio can concentrate more analyte molecules to the surface of the SERS substrates, which can help to detect biomolecules that cannot be easily adsorbed by metallic nanoparticles.

Mars atmosphere. Mars methane detection and variability at Gale crater.

Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source.

Characterization of organics, microorganisms, desert soils, and Mars-like soils by thermal volatilization coupled to mass spectrometry and their implications for the search for organics on Mars by Phoenix and future space missions.

A key goal for astrobiology is the search for evidence of life on Mars. Because liquid water is a fundamental environmental requirement for life, the recent set of missions to Mars have focused on a strategy known as "follow the water." Since life is made of organic molecules, a logical next step is "follow the organics." However, organics are expected to be present at very low levels on Mars, which would make their detection challenging. Viking was unable to detect organics at parts per billion (ppb), but the effective upper limit could be higher due to the low efficiency of the thermal volatilization (TV) step in releasing organics. Due to its ease of use, TV is still the method selected for current and future NASA and ESA missions. Here, we show that when organics are present in the soil at levels above 1500 parts per million (ppm), there are several characteristic organic fragments detected by TV-mass spectrometry; however, when the levels are below <150 ppm, TV oxidizes them, and no organic fragments are released. Instead, nitric oxide (NO) is produced and can be used to determine quantitatively the organic content if the C/N ratio is determined. Any atmospheric NO sorbed or mineral nitrogen (e.g., nitrates) present in the soil would release NO by TV at distinctive temperature regimes that would not overlap with the organic nitrogen source. Therefore, we suggest that monitoring NO provides the best chance for Phoenix and other future Mars missions to detect nitrogen-containing organics in the soil or ice.

Description of four novel psychrophilic, ionizing radiation-sensitive Deinococcus species from alpine environments.

Five psychrophilic bacterial strains were isolated from soil samples collected above the treeline of alpine environments. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these organisms represent four novel species of the genus Deinococcus; levels of sequence similarity to the type strains of recognized Deinococcus species were in the range 89.3-94.7 %. Strains PO-04-20-132T, PO-04-20-144, PO-04-19-125T, ME-04-01-32T and ME-04-04-52T grew aerobically, with optimum growth at 10 degrees C and at pH 6-9. The major respiratory menaquinone was MK-8. The fatty acid profiles of strains PO-04-20-132T, PO-04-20-144, PO-04-19-125T and ME-04-01-32T were dominated by 16 : 1omega7c, 17 : 0 iso and 15 : 1omega6c, whereas 16 : 1omega7c, 17 : 0 cyclo and 16 : 0 predominated in strain ME-04-04-52T. The DNA G+C contents of strains PO-04-20-132T, PO-04-19-125T, ME-04-01-32T and ME-04-04-52T were 63.2, 63.1, 65.9 and 62.6 mol%, respectively. Strains PO-04-20-132T, PO-04-19-125T, ME-04-01-32T and ME-04-04-52T had gamma radiation D10 (dose required to reduce the bacterial population by 10-fold) values of < or =4 kGy. These four strains showed sensitivity to UV radiation and extended desiccation as compared with Deinococcus radiodurans. On the basis of the phylogenetic analyses, and chemotaxonomic and phenotypic data, it is proposed that strains PO-04-20-132T (=LMG 24019T=NRRL B-41950T; Deinococcus radiomollis sp. nov.), PO-04-19-125T (=LMG 24282T=NRRL B-41949T; Deinococcus claudionis sp. nov.), ME-04-01-32T (=LMG 24022T=NRRL B-41947T; Deinococcus altitudinis sp. nov.) and ME-04-04-52T (=LMG 24283T=NRRL B-41948T; Deinococcus alpinitundrae sp. nov.) represent the type strains of four novel species of the genus Deinococcus.

The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results.

The failure of Viking Lander thermal volatilization (TV) (without or with thermal degradation)-gas chromatography (GC)-MS experiments to detect organics suggests chemical rather than biological interpretations for the reactivity of the martian soil. Here, we report that TV-GC-MS may be blind to low levels of organics on Mars. A comparison between TV-GC-MS and total organics has been conducted for a variety of Mars analog soils. In the Antarctic Dry Valleys and the Atacama and Libyan Deserts we find 10-90 mug of refractory or graphitic carbon per gram of soil, which would have been undetectable by the Viking TV-GC-MS. In iron-containing soils (jarosites from Rio Tinto and Panoche Valley) and the Mars simulant (palogonite), oxidation of the organic material to carbon dioxide (CO(2)) by iron oxides and/or their salts drastically attenuates the detection of organics. The release of 50-700 ppm of CO(2) by TV-GC-MS in the Viking analysis may indicate that an oxidation of organic material took place. Therefore, the martian surface could have several orders of magnitude more organics than the stated Viking detection limit. Because of the simplicity of sample handling, TV-GC-MS is still considered the standard method for organic detection on future Mars missions. We suggest that the design of future organic instruments for Mars should include other methods to be able to detect extinct and/or extant life.