Can Plants Grow on Mars and the Moon: A Growth Experiment on Mars and Moon Soil Simulants

When humans will settle on the moon or Mars they will have to eat there. Food may be flown in. An alternative could be to cultivate plants at the site itself, preferably in native soils. We report on the first large-scale controlled experiment to investigate the possibility of growing plants in Mars and moon soil simulants. The results show that plants are able to germinate and grow on both Martian and moon soil simulant for a period of 50 days without any addition of nutrients. Growth and flowering on Mars regolith simulant was much better than on moon regolith simulant and even slightly better than on our control nutrient poor river soil. Reflexed stonecrop (a wild plant); the crops tomato, wheat, and cress; and the green manure species field mustard performed particularly well. The latter three flowered, and cress and field mustard also produced seeds. Our results show that in principle it is possible to grow crops and other plant species in Martian and Lunar soil simulants. However, many questions remain about the simulants'' water carrying capacity and other physical characteristics and also whether the simulants are representative of the real soils.     

Low Pressure Tolerance by Methanogens in an Aqueous Environment: Implications for Subsurface Life on Mars

The low pressure at the surface of Mars (average: 6 mbar) is one potentially biocidal factor that any extant life on the planet would need to endure. Near subsurface life, while shielded from ultraviolet radiation, would also be exposed to this low pressure environment, as the atmospheric gas-phase pressure increases very gradually with depth. Few studies have focused on low pressure as inhibitory to the growth or survival of organisms. However, recent work has uncovered a potential constraint to bacterial growth below 25 mbar. The study reported here tested the survivability of four methanogen species (Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, Methanococcus maripaludis) under low pressure conditions approaching average martian surface pressure (6 mbar – 143 mbar) in an aqueous environment. Each of the four species survived exposure of varying length (3 days – 21 days) at pressures down to 6 mbar. This research is an important stepping-stone to determining if methanogens can actively metabolize/grow under these low pressures. Additionally, the recently discovered recurring slope lineae suggest that liquid water columns may connect the surface to deeper levels in the subsurface. If that is the case, any organism being transported in the water column would encounter the changing pressures during the transport.     

Effect of Surface Plasma Treatments on the Adhesion of Mars JSC 1 Simulant Dust to RTV 655, RTV 615, and Sylgard 184

Background

Dust accumulation on surfaces of critical instruments has been a major concern during lunar and Mars missions. Operation of instruments such as solar panels, chromatic calibration targets, as well as Extra Vehicular Activity (EVA) suits has been severely compromised in the past as a result of dust accumulation and adhesion. Wind storms with wind speeds of up to 70 mph have not been effective in removing significant amounts of the deposited dust. This is indeed an indication of the strength of the adhesion force(s) involved between the dust particles and the surface(s) that they have adhered to. Complications associated with dust accumulation are more severe for non-conducting surfaces and have been the focus of this work.

Methodology

Argon plasma treatment was investigated as a mechanism for lowering dust accumulation on non-conducting polymeric surfaces. Polymers chosen for this study include a popular variety of silicones routinely used for space and terrestrial applications namely RTV 655, RTV 615, and Sylgard 184. Surface properties including wettability, surface potential, and surface charge density were compared before and after plasma treatment and under different storage conditions. Effect of ultraviolet radiation on RTV 655 was also investigated and compared with the effect of Ar plasma treatment.

Conclusion/Significance

Gravimetric measurements proved Ar plasma treatment to be an effective method for eliminating dust adhesion to all three polymers after short periods of exposure. No physical damage was detected on any of the polymer surfaces after Ar plasma treatment. The surface potential of all three polymers remained zero up to three months post plasma exposure. Ultraviolet radiation however was not effective in reducing surface and caused damage and significant discoloration to RTV 655. Therefore, Ar plasma treatment can be an effective and non-destructive method for treating insulating polymeric surfaces in order to eliminate dust adhesion and accumulation.     

H2-CO2 Recirculation and pH Control for Growth of Methanogens in Mass Culture

We modified a fermentor (10-liter liquid volume) for the growth of anaerobic, H₂-CO₂-catabolizing bacteria. Gas in the fermentor (ca. 10% CO₂, 50% H₂, 40% CH₄) was recirculated by a diaphragm pump. During growth, the gas composition was maintained by the addition of a mixture of 80% H₂ and 20% CO₂, and this addition was controlled by a pH auxostat. During gas addition, gas was discharged from the recirculating gas stream and was collected by the displacement of an acidified salt solution.     

Methanogens: a window into ancient sulfur metabolism

Methanogenesis is an ancient metabolism that originated on the early anoxic Earth. The buildup of O(2) about 2.4 billion years ago led to formation of a large oceanic sulfate pool, the onset of widespread sulfate reduction and the marginalization of methanogens to anoxic and sulfate-poor niches. Contemporary methanogens are restricted to anaerobic habitats and may have retained some metabolic relics that were common in early anaerobic life. Consistent with this hypothesis, methanogens do not utilize sulfate as a sulfur source, Cys is not utilized as a sulfur donor for Fe-S cluster and Met biosynthesis, and Cys biosynthesis uses an unusual tRNA-dependent pathway.     

Growth of Azotobacter vinelandii on Soil Nutrients

Azotobacter vinelandii cells grew well in a medium made from soil and distilled water which contained little or no carbohydrate. They utilized p-hydroxybenzoic acid and other phenolic acids, soil nitrogen, and water-soluble mineral substances. Seventeen soils which supported excellent growth of A. vinelandii contained 11 to 18 different phenolic acids each, including p-hydroxybenzoic, m-hydroxybenzoic, vanillic, p-coumeric, syringic, cis- and trans-ferrulic, and other unidentified aromatic acids. Three white, chalky “caliche” soils which were taken from areas where no plants grew failed to support the growth of A. vinelandii, and these contained no, two, and three phenolic acids, respectively. A. vinelandii did not fix nitrogen when growing in dialysates of soils which contained numerous phenolic acids. Growth was ample and rapid in most of the soils tested, but cell morphology was different from that usually seen in chemically defined, nitrogen-free media which contain glucose.     

Hydrogen Consumption by Methanogens on the Early Earth

It is possible that the first autotroph used chemical energy rather than light. This could have been the main source of primary production after the initial inventory of abiotic organic material had been depleted. The electron acceptor most readily available for use by this first chemoautotroph would have been CO₂. The most abundant electron donor may have been H₂ that would have been outgassing from volcanoes at a rate estimated to be as large as 10¹² moles yr^–1, as well as from photo-oxidation of Fe⁺². We report here that certain methanogens will consume H₂ down to partial pressures as low as 4 Pa (4 × 10^–5 atm) with CO₂ as the sole carbon source at a rate of 0.7 ng H₂ min^–1 g^–1 cell protein. The lower limit of pH₂ for growth of methanogens can be understood on the basis that the pH₂ needs to be high enough for one ATP to be synthesized per CO₂ reduced. The pH₂ values needed for growth measured here are consistent with those measured by Stevens and McKinley for growth of methanogens in deep basalt aquifers. H₂-consuming autotrophs are likely to have had a profound effect on the chemistry of the early atmosphere and to have been a dominant sink for H₂ on the early Earth after life began rather than escape from the Earth's atmosphere to space.     

Activity and Diversity of Methanogens in a Petroleum Hydrocarbon-Contaminated Aquifer

Methanogenic activity was investigated in a petroleum hydrocarbon-contaminated aquifer by using a series of four push-pull tests with acetate, formate, H₂ plus CO₂, or methanol to target different groups of methanogenic Archaea. Furthermore, the community composition of methanogens in water and aquifer material was explored by molecular analyses, i.e., fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes amplified with the Archaea-specific primer set ARCH915 and UNI-b-rev, and sequencing of DNA from dominant DGGE bands. Molecular analyses were subsequently compared with push-pull test data. Methane was produced in all tests except for a separate test where 2-bromoethanesulfonate, a specific inhibitor of methanogens, was added. Substrate consumption rates were 0.11 mM day⁻¹ for methanol, 0.38 mM day⁻¹ for acetate, 0.90 mM day⁻¹ for H₂, and 1.85 mM day⁻¹ for formate. Substrate consumption and CH₄ production during all tests suggested that at least three different physiologic types of methanogens were present: H₂ plus CO₂ or formate, acetate, and methanol utilizers. The presence of 15 to 20 bands in DGGE profiles indicated a diverse archaeal population. High H₂ and formate consumption rates agreed with a high diversity of methanogenic Archaea consuming these substrates (16S rRNA gene sequences related to several members of the Methanomicrobiaceae) and the detection of Methanomicrobiaceae by using FISH (1.4% of total DAPI [4′,6-diamidino-2-phenylindole]-stained microorganisms in one water sample; probe MG1200). Considerable acetate consumption agreed with the presence of sequences related to the obligate acetate degrader Methanosaeata concilii and the detection of this species by FISH (5 to 22% of total microorganisms; probe Rotcl1). The results suggest that both aceticlastic and CO₂-type substrate-consuming methanogens are likely involved in the terminal step of hydrocarbon degradation, while methanogenesis from methanol plays a minor role. DGGE profiles further indicate similar archaeal community compositions in water and aquifer material. The combination of hydrogeological and molecular methods employed in this study provide improved information on the community and the potential activity of methanogens in a petroleum hydrocarbon-contaminated aquifer.     

Life on Mars

Abstract

There is evidence that at one time Mars had liquid water habitats on its surface. Studies of microbial communities in cold and dry environments on the Earth provide a basis for discussion of the possible nature of any life that may have existed on Mars during that time. Of particular relevance are the cyanobacterial communities found in hypolithic and endolithic habitats in deserts. Microbial mats found under ice-covered lakes provide an additional possible Martian system. Results obtained from these field studies can be used to guide the search for fossil evidence of life on Mars. It is possible that in the future life will be reintroduced on Mars in an effort to restore that planet to habitable conditions. In this case the organisms under study as exemplars of past life may provide the hardy stock of pioneering Martian organisms. These first organisms must be followed by plants. The feasibility of reviving Mars will depend on the ability of plants to grow in an abundance of CO₂ but at extremely low pressures, temperatures, O₂, and N₂ levels. On Mars, biology was, and is, destiny.     

Anaerobic 2-Propanol Degradation in Anoxic Paddy Soil and the Possible Role of Methanogens in Its Degradation

The anaerobic degradation of 2-propanol in anoxic paddy soil was studied with soil cultures and a 2-propanol-utilizing methanogen. Acetone was the first and the major intermediate involved in the methanogenic degradation of 2-propanol. Analyses with a methanogenesis inhibitor, bacteria antibiotics, and the addition of H₂ to the gas phase revealed that 2-propanol oxidation to acetone directly occurred using 2-propanol-utilizing methanogens, but not with H₂-producing syntrophic bacteria, for which the removal of acetone is required for complete 2-propanol oxidation. The 2-propanol-utilizing strain IIE1, which is phylogenetically closely related to Methanoculleus palmolei, was isolated from paddy soil, and the potential role of the strain in 2-propanol degradation was investigated. 2-Propanol is one of the representative fermentation intermediates in anaerobic environments. This is the first report on the anaerobic 2-propanol degradation process.     

Hydrogenotrophic Methanogenesis by Moderately Acid-Tolerant Methanogens of a Methane-Emitting Acidic Peat

The emission of methane (1.3 mmol of CH₄ m⁻² day⁻¹), precursors of methanogenesis, and the methanogenic microorganisms of acidic bog peat (pH 4.4) from a moderately reduced forest site were investigated by in situ measurements, microcosm incubations, and cultivation methods, respectively. Bog peat produced CH₄ (0.4 to 1.7 μmol g [dry wt] of soil⁻¹ day⁻¹) under anoxic conditions. At in situ pH, supplemental H₂-CO₂, ethanol, and 1-propanol all increased CH₄ production rates while formate, acetate, propionate, and butyrate inhibited the production of CH₄; methanol had no effect. H₂-dependent acetogenesis occurred in H₂-CO₂-supplemented bog peat only after extended incubation periods. Nonsupplemented bog peat initially produced small amounts of H₂ that were subsequently consumed. The accumulation of H₂ was stimulated by ethanol and 1-propanol or by inhibiting methanogenesis with bromoethanesulfonate, and the consumption of ethanol was inhibited by large amounts of H₂; these results collectively indicated that ethanol- or 1-propanol-utilizing bacteria were trophically associated with H₂-utilizing methanogens. A total of 10⁹ anaerobes and 10⁷ hydrogenotrophic methanogens per g (dry weight) of bog peat were enumerated by cultivation techniques. A stable methanogenic enrichment was obtained with an acidic, H₂-CO₂-supplemented, fatty acid-enriched defined medium. CH₄ production rates by the enrichment were similar at pH 4.5 and 6.5, and acetate inhibited methanogenesis at pH 4.5 but not at pH 6.5. A total of 27 different archaeal 16S rRNA gene sequences indicative of Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae were retrieved from the highest CH₄-positive serial dilutions of bog peat and methanogenic enrichments. A total of 10 bacterial 16S rRNA gene sequences were also retrieved from the same dilutions and enrichments and were indicative of bacteria that might be responsible for the production of H₂ that could be used by hydrogenotrophic methanogens. These results indicated that in this acidic bog peat, (i) H₂ is an important substrate for acid-tolerant methanogens, (ii) interspecies hydrogen transfer is involved in the degradation of organic carbon, (iii) the accumulation of protonated volatile fatty acids inhibits methanogenesis, and (iv) methanogenesis might be due to the activities of methanogens that are phylogenetic members of the Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae.     

Biochemical Characterization of a Dihydroneopterin Aldolase Used for Methanopterin Biosynthesis in Methanogens

The gene encoding 7,8-dihydroneopterin aldolase (DHNA) was recently identified in archaea through comparative genomics as being involved in methanopterin biosynthesis (V. Crécy-Lagard, G. Phillips, L. L. Grochowski, B. El Yacoubi, F. Jenney, M. W. Adams, A. G. Murzin, and R. H. White, ACS Chem. Biol. 7:1807–1816, 2012, doi:10.1021/cb300342u). Archaeal DHNA shows a unique secondary and quaternary structure compared with bacterial and plant DHNAs. Here, we report a detailed biochemical examination of DHNA from the methanogen Methanocaldococcus jannaschii. Kinetic studies show that M. jannaschii DHNA possesses a catalytic capability with a k_cat/K_m above 10⁵ M⁻¹ s⁻¹ at 70°C, and at room temperature it exhibits a turnover number (0.07 s⁻¹) comparable to bacterial DHNAs. We also found that this enzyme follows an acid-base catalytic mechanism similar to the bacterial DHNAs, except when using alternative catalytic residues. We propose that in the absence of lysine, which is considered to be the general base in bacterial DHNAs, an invariant water molecule likely functions as the catalytic base, and the strictly conserved His35 and Gln61 residues serve as the hydrogen bond partners to adjust the basicity of the water molecule. Indeed, substitution of either His35 or Gln61 causes a 20-fold decrease in k_cat. An invariant Tyr78 is also shown to be important for catalysis, likely functioning as a general acid. Glu25 plays an important role in substrate binding, since replacing Glu25 by Gln caused a ≥25-fold increase in K_m. These results provide important insights into the catalytic mechanism of archaeal DHNAs.     

产甲烷菌研究进展

产甲烷菌是重要的环境微生物,在自然界的碳素循环中起重要作用。迄今已有5种产甲烷菌基因组测序完成。基因组信息使人们对产甲烷茵的细胞结构、进化、代谢及环境适应性有了更深的理解。目前已知的甲烷生物合成途径有3种,它们以乙酸、甲基化合物、氢/二氧化碳为起始,通过不同的反应途径都形成了甲基辅酶M,在甲基辅酶M还原酶的催化下最终形成甲烷。     

Microbial Growth in a Steady-State Model of Ethylene Glycol-Contaminated Soil

Biodegradation of ethylene glycol was tested in a laboratory-scale, steady-state infiltration system of two arid region soil types by monitoring indigenous microbial growth after the infiltration of three concentrations of ethylene glycol. Microorganisms in the soils were able to adapt to the ethylene glycol in several cases, resulting in higher numbers of microorganisms and lower pHs in the effluents. These microorganisms were identified and were able to use ethylene glycol as a sole carbon source. The adaptation was seen best with high-moisture-content soils when the ethylene glycol concentrations were 1% or 10%. However, acclimation to 0.1% and 10% ethylene glycol did not occur in low-moisture-content clay soil, but did occur in low-moisture-content silt soil, indicating that soil type and moisture content are important factors. In all cases, microbial diversity decreased over time. Received: 23 June 1997 / Accepted: 11 August 1997     

Laboratory investigations of mars: Chemical and spectroscopic characteristics of a suite of clays as Mars Soil Analogs

Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils.     

Effects of Simulated Mars Conditions on the Survival and Growth of Escherichia coli and Serratia liquefaciens

Escherichia coli and Serratia liquefaciens, two bacterial spacecraft contaminants known to replicate under low atmospheric pressures of 2.5 kPa, were tested for growth and survival under simulated Mars conditions. Environmental stresses of high salinity, low temperature, and low pressure were screened alone and in combination for effects on bacterial survival and replication, and then cells were tested in Mars analog soils under simulated Mars conditions. Survival and replication of E. coli and S. liquefaciens cells in liquid medium were evaluated for 7 days under low temperatures (5, 10, 20, or 30°C) with increasing concentrations (0, 5, 10, or 20%) of three salts (MgCl₂, MgSO₄, NaCl) reported to be present on the surface of Mars. Moderate to high growth rates were observed for E. coli and S. liquefaciens at 30 or 20°C and in solutions with 0 or 5% salts. In contrast, cell densities of both species generally did not increase above initial inoculum levels under the highest salt concentrations (10 and 20%) and the four temperatures tested, with the exception that moderately higher cell densities were observed for both species at 10% MgSO₄ maintained at 20 or 30°C. Growth rates of E. coli and S. liquefaciens in low salt concentrations were robust under all pressures (2.5, 10, or 101.3 kPa), exhibiting a general increase of up to 2.5 orders of magnitude above the initial inoculum levels of the assays. Vegetative E. coli cells were maintained in a Mars analog soil for 7 days under simulated Mars conditions that included temperatures between 20 and −50°C for a day/night diurnal period, UVC irradiation (200 to 280 nm) at 3.6 W m⁻² for daytime operations (8 h), pressures held at a constant 0.71 kPa, and a gas composition that included the top five gases found in the martian atmosphere. Cell densities of E. coli failed to increase under simulated Mars conditions, and survival was reduced 1 to 2 orders of magnitude by the interactive effects of desiccation, UV irradiation, high salinity, and low pressure (in decreasing order of importance). Results suggest that E. coli may be able to survive, but not grow, in surficial soils on Mars.The search for extant life on Mars remains a stated goal of NASA''s Mars Exploration Program and Astrobiology Institutes (13, 17). Intrinsic within such a life detection strategy is a requirement to understand how terrestrial life might survive, replicate, and proliferate on Mars. To mitigate the risks of the forward contamination of Mars, the bioloads on spacecrafts targeted for landing must be reduced to low density and diversity (4, 7). Planetary protection guidelines are designed to prevent both the forward contamination of the martian surface and to ensure the scientific integrity of any deployed life detection experiments. To date, 12 spacecraft have landed or crashed onto the Mars surface as a result of U.S., Russian, and European space program missions, but it is currently unknown if terrestrial microorganisms typically found on spacecraft surfaces can grow and replicate under conditions encountered on the surface (44, 45, 48).Despite cleaning and sterilization measures taken to significantly reduce microbial bioloads on spacecraft (26, 56), diverse microbial communities remain at the time of launch (7, 31, 32, 44). The diversity of microorganisms found on spacecraft surfaces are generally characteristic of the clean rooms within which the spacecraft are processed. Spacecraft assembly facilities are oligotrophic extreme environments in which only the most resilient species survive the high-desiccation, low-nutrient conditions, controlled air circulation, and the rigors of bioburden reduction (56, 57). The biological inventory of microorganisms on spacecraft has mostly been limited to isolation and identification using standard culture-based microbiological assays (44, 48, 53). However, culture-based microbiological assays likely underestimate the biological diversity present on spacecraft, as traditional culture techniques fail to capture more than 99.9% of present phylotypes (7). Recently, the simultaneous use of culture-dependent and culture-independent techniques (e.g., Limulus amoebocyte lysate assay [LAL], ATP bioluminescence assay, lipopolysaccharide-based microbial detection, and DNA-based PCR) have identified many nonculturable species (31, 32, 57). Known culturable bacteria recovered from spacecraft surfaces include, but are not limited to, species of Acinetobacter, Bacillus, Corynebacterium, Escherichia, Flavobacterium, Micrococcus, Pseudomonas, Serratia, Staphylococcus, and Streptococcus (44, 53, 57).After launch, spacecraft are exposed to interplanetary conditions of ultralow pressure (3 × 10⁻¹⁰ kPa), extreme desiccating conditions, fluctuating temperatures, solar UV irradiation, and ionizing radiation (22, 44). Furthermore, upon landing, the conditions on the surface of Mars are not much improved over interplanetary space. Diverse biocidal or inhibitory conditions on Mars have been identified in a number of recent publications (8, 21, 22, 35, 36, 38, 44, 48, 59) and include the following (not in order of priority): solar UVC irradiation, low pressure, extreme desiccating conditions, extreme diurnal temperature fluctuations, solar particle events, galactic cosmic rays, UV glow discharge from blowing dust, solar UV-induced volatile oxidants (e.g., O₂⁻, O⁻, H₂O₂, NO_x, O₃), globally distributed oxidizing soils, extremely high salt levels (e.g., MgCl₂, NaCl, FeSO₄, and MgSO₄) in surficial soils at some sites on Mars, high concentrations of heavy metals in martian soils, acidic conditions in martian regolith, high CO₂ concentrations in the global atmosphere, and presence of perchlorates in some regoliths. UV irradiation, especially UVC photons (200 to 280 nm), may be the most biocidal of all factors to microbial survival on the martian surface (34, 37, 39, 47, 50, 52). Microorganisms found on sun-exposed surfaces of spacecraft are killed off within a few tens of minutes of exposure; but if covered by as little as a few hundred micrometers of martian soil, significant protection is provided (11, 34, 47). It is currently unknown if terrestrial microorganisms typically found on spacecraft surfaces can grow and replicate under conditions encountered on the surface of Mars (44, 48).In the studies cited above, most research focused on the survival of dormant spores or vegetative cells under Mars conditions. In contrast, only a few papers have explored the possibility of growth and replication of terrestrial microorganisms under environmental conditions that approach those found in surficial soils of Mars (5, 25, 45, 48). Of these four, 2.5 kPa is the lowest pressure at which replication was observed for a few bacterial species (5, 45, 48).The primary objective of the current study was to expose two non-spore-forming species to environmental stresses present on the surface of Mars to characterize the potential response of the bacteria to martian temperatures, salinities, and pressures. Two bacterial species, Escherichia coli and Serratia liquefaciens, were selected from over 30 prokaryotic species tested in preliminary experiments (5, 45). Their selection was based on their common association with humans, recovery from robotic spacecraft and space-based human life support systems (44, 53), and demonstrated replication at 2.5 kPa of total atmospheric pressure (5, 45). Experiments were conducted on cell suspensions in liquid medium at combinations of low pressure, high salt concentrations, and low temperatures, and then with cells mixed into soils and exposed to simulated Mars conditions. It was predicted for cell suspensions that (i) low temperatures would dramatically retard cell proliferation, (ii) high concentrations of salts would be biocidal on cell suspensions, and (iii) low pressure would have weak to moderate inhibitory effects on cell growth of both species. For cells in soils, growth was not expected under Mars simulations which exposed vegetative cells to low pressure, low temperatures, anaerobic gas composition, and high UVC irradiation similar to the martian surface. Although replication was not predicted, bacterial survival in analog Mars soils under simulated Mars conditions was anticipated.