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Physiological and gene expression studies of deep-sea bacteria under pressure conditions similar to those experienced in their natural habitat are critical for understanding growth kinetics and metabolic adaptations to in situ conditions. The Campylobacterium (aka Epsilonproteobacterium) Nautilia sp. strain PV-1 was isolated from hydrothermal fluids released from an active deep-sea hydrothermal vent at 9° N on the East Pacific Rise. Strain PV-1 is a piezophilic, moderately thermophilic, chemolithoautotrophic anaerobe that conserves energy by coupling the oxidation of hydrogen to the reduction of nitrate or elemental sulfur. Using a high-pressure-high temperature continuous culture system, we established that strain PV-1 has the shortest generation time of all known piezophilic bacteria and we investigated its protein expression pattern in response to different hydrostatic pressure regimes. Proteogenomic analyses of strain PV-1 grown at 20 and 5 MPa showed that pressure adaptation is not restricted to stress response or homeoviscous adaptation but extends to enzymes involved in central metabolic pathways. Protein synthesis, motility, transport, and energy metabolism are all affected by pressure, although to different extents. In strain PV-1, low-pressure conditions induce the synthesis of phage-related proteins and an overexpression of enzymes involved in carbon fixation.

Understanding the viscosity of mantle-derived magmas is needed to model their migration mechanisms and ascent rate from the source rock to the surface. High pressure–temperature experimental data are now available on the viscosity of synthetic melts, pure carbonatitic to carbonate–silicate compositions, anhydrous basalts, dacites and rhyolites. However, the viscosity of volatile-bearing melilititic melts, among the most plausible carriers of deep carbon, has not been investigated. In this study, we experimentally determined the viscosity of synthetic liquids with ~31 and ~39 wt% SiO2, 1.60 and 1.42 wt% CO2 and 5.7 and 1 wt% H2O, respectively, at pressures from 1 to 4.7 GPa and temperatures between 1265 and 1755 °C, using the falling-sphere technique combined with in situ X-ray radiography. Our results show viscosities between 0.1044 and 2.1221 Pa·s, with a clear dependence on temperature and SiO2 content. The atomic structure of both melt compositions was also determined at high pressure and temperature, using in situ multi-angle energy-dispersive X-ray diffraction supported by ex situ microFTIR and microRaman spectroscopic measurements. Our results yield evidence that the T–T and T–O (T = Si,Al) interatomic distances of ultrabasic melts are higher than those for basaltic melts known from similar recent studies. Based on our experimental data, melilititic melts are expected to migrate at a rate ~from 2 to 57 km·yr−1 in the present-day or the Archaean mantle, respectively.

This study analyzed samples of the Murchison and Sutter's Mill carbonaceous chondrite meteorites in support of the future analysis of samples returned from the asteroid (10155) Bennu by the OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission. Focusing specifically on the insoluble organic matter (IOM), this study establishes that a total of 1.3 g of bulk sample from a single chondritic meteorite are sufficient to obtain a wide range of cosmochemical information, including light element analysis (H, C, and N), isotopic analysis (D/H, 13C/12C, and 15N/14N), and x‐ray fluorescence spectroscopy for major elemental abundances. IOM isolated from the bulk meteorite samples was analyzed by light element and isotopic analysis as described above, 1H and 13C solid‐state nuclear magnetic resonance spectroscopy, Raman spectroscopy, and complete noble gas analyses (abundances and isotopes). The samples studied included a pair from Murchison (CM2), one of which had been irradiated with high‐energy x‐rays in the course of computed tomographic imaging. No differences between the irradiated and non‐irradiated Murchison samples were observed in the many different chemical and spectroscopic analyses, indicating that any x‐ray–derived sample damage is below levels of detection. Elemental, isotopic, and molecular spectroscopic data derived from IOM isolated from the Sutter's Mill sample reveals evidence that this meteorite falls into the class of heated CM chondrites. [ABSTRACT FROM AUTHOR]

Microbial sulfur cycling in marine sediments often occurs in environments characterized by transient chemical gradients that affect both the availability of nutrients and the activity of microbes. High turnover rates of intermediate valence sulfur compounds and the intermittent availability of oxygen in these systems greatly impact the activity of sulfur‐oxidizing micro‐organisms in particular. In this study, the thiosulfate‐oxidizing hydrothermal vent bacterium Thiomicrospira thermophila strain EPR85 was grown in continuous culture at a range of dissolved oxygen concentrations (0.04–1.9 mM) and high pressure (5–10 MPa) in medium buffered at pH 8. Thiosulfate oxidation under these conditions produced tetrathionate, sulfate, and elemental sulfur, in contrast to previous closed‐system experiments at ambient pressure during which thiosulfate was quantitatively oxidized to sulfate. The maximum observed specific growth rate at 5 MPa pressure under unlimited O2 was 0.25 hr−1. This is comparable to the μmax (0.28 hr−1) observed at low pH (<6) at ambient pressure when T. thermophila produces the same mix of sulfur species. The half‐saturation constant for O2 (KO2) estimated from this study was 0.2 mM (at a cell density of 105 cells/ml) and was robust at all pressures tested (0.4–10 MPa), consistent with piezotolerant behavior of this strain. The cell‐specific KO2 was determined to be 1.5 pmol O2/cell. The concentrations of products formed were correlated with oxygen availability, with tetrathionate production in excess of sulfate production at all pressure conditions tested. This study provides evidence for transient sulfur storage during times when substrate concentration exceeds cell‐specific KO2 and subsequent consumption when oxygen dropped below that threshold. These results may be common among sulfur oxidizers in a variety of environments (e.g., deep marine sediments to photosynthetic microbial mats). [ABSTRACT FROM AUTHOR]

Continuous culture under elevated pressures is an important technique for expanding the exploration of microbial growth and survival in extreme environments associated with the deep biosphere. Here we present a benchtop stirred continuous culture bioreactor capable of withstanding temperatures ranging from 25 to 120°C and pressures as high as 69 MPa. The system is configured to allow the employment of media enriched in dissolved gases, under oxic or anoxic conditions, while permitting periodic sampling of the incubated organisms with minimal physical/chemical disturbance inside the reactor. In a pilot experiment, the fermentative growth of the thermopiezophilic bacterium Marinitoga piezophila was investigated continuously for 382 h at 65°C and at pressures ranging from 0.1 to 40 MPa while the medium flow rate was varied from 2 to 0.025 ml/min. The enhanced growth observed at 30 and 40 MPa and 0.025 ml/min supports the pressure preferences of M. piezophila when grown fermentatively. This assay successfully demonstrates the capabilities of the bioreactor for continuous culturing at a variety of dilution rates, pressures, and temperatures. We anticipate that this technology will accelerate our understanding of the physiological and metabolic status of microorganisms under temperature, pressure, and energy regimes resembling those of the Earth's piezosphere. [ABSTRACT FROM AUTHOR]

The structure of water-saturated Ca- and Mg-bearing carbonate melts under reducing and oxidizing conditions was investigated in a series of hydrothermal anvil cell experiments conducted at 400-1100 °C and 442-2839 MPa. Equilibria were investigated in the calcite-H2O, calcite-CaO-H2O, magnesite-H2O, and magnesite-MgO-H2O systems, with redox conditions controlled by Re/ReO2 and Ti/TiO2 assemblages. Melting relationships and the C-O-H speciation of the coexisting aqueous fluid and melt were assessed in situ by Raman vibrational spectroscopy. Hydrous melting of MgCO3-MgO occurred at ~850 °C, 1.5-2 GPa. In the CaCO3-CaO-H2O system, melt was formed at 600-900 °C and pressures of 0.5-1.5 GPa because of melting-point depression imposed by the presence of CaO. The C-O-H speciation of the carbonate melts and coexisting supercritical aqueous solutions was mainly H2O and CO2-3, with traces of CO2(aq) and CH4(aq) in the fluid phase. The melt-fluid H2O partition coefficients attained in the Mg-bearing melt (median 0.5) were higher than in the Ca-bearing melt (median 0.3). Under oxidizing redox conditions, dissolved ReO-2 was present in all phases, underscoring the enhanced solubility of metals in carbonate-bearing melts and carbonatites. In effect, the enhanced solubility of H2O along with the ionic nature of the carbonate melts may promote the solvation of ionic species in the melt structure. From in situ vibrational spectroscopy, the v1-CO2-3vibration recorded in the melt spectra suggests the presence of intermolecular interactions between the oxygen of the carbonate ion with water dissolved in the melt. The thermodynamic properties of this water appear to be similar to the supercritical aqueous phase. For example, the estimated enthalpy for the breakage of the hydrogen bonding between water molecules attained values of 6.8 ± 1.5 kcal/mol and 8.4 ± 1.3 kcal/mol in the melt and fluid phase, respectively. The calculated partial molar volume of H2O in the melt (~48 ± 6 cm³/mol) is also comparable to the partial molar volume of supercritical water at similar conditions. Interestingly, this value is considerably greater than published partial molar volume values for H2O in silicate melts (10-12 cm³/mol). The pressure-temperature melting relationships of the CaO-CO2-H2O and MgO-CO2-H2O systems highlight the important role of water and alkaline earth oxides on the hydrous melting of the carbonate-bearing subducting oceanic crust. Carbonates present in marine sediments or serpentinized peridotites may melt before complete dehydration at the slab-mantle wedge transition zone, and thus, never reach sub-arc depths. To this end, melting of carbonate minerals at crustal temperatures and pressure can contribute to the volcanic CO2 flux at the arc through melt/fluid interactions. [ABSTRACT FROM AUTHOR]

A series of hydrothermal diamond-anvil cell experiments have been conducted to evaluate the role of supercritical water on the isotopic equilibrium between H/D methane isotopologues at 600-800 °C and 409-1622 MPa. Raman spectroscopy was deployed to investigate the distribution of H/D isotopic molecules formed during hydrothermal decomposition of Si5C12H36 in H2O-D2O aqueous solutions. To this end, the intensities of the fundamental vibrational C-H and C-D modes of deuteromethanes were employed to determine the thermodynamic properties of isotope exchange reactions between H/D isotopologues and to constrain the methane D/H molar ratios. By adjusting the initial volume ratios of silane/H2O-D2O, reactions in the CH4-D2O-H2O system were monitored for gaseous and supercritical-water phases. Discreet differences between the equilibrium constants, describing the relationship between the CH3D-CH2D2-CHD3-CH4 species dissolved in supercritical water or present as a homogeneous gas phase, are revealed. The bulk D/H methane composition in the liquid-system is also twice that of the D/H molar ratios recorded in the gas-bearing system. Accordingly, condensed-phase isotope effects are inferred to play a key role on the evolution of H/D isotopologues, likely induced by differences in the solubility of the isotopic molecules driven by the excess energy/entropy developed during mixing of non-polar species in the H2O-D2O structure. Our experiments show that isotope fractionation effects need to account for the presence of condensed matter (e.g., melts, magmatic fluids), even at conditions at which theoretical models suggest minimal (or nonexistent) isotope exchange, but comparable to those within the Earth's interior. [ABSTRACT FROM AUTHOR]

The presence of graphite in natural environments is linked to the redox and thermal conditions of C-H-O fluid/graphite equilibrium in hydrothermal veins and metasomatic contacts. A time-series experimental study was performed to investigate the graphite undersaturated C-H-O system at 600 °C and 1000 MPa, and with Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed ranging from highly reducing (10-23) to highly oxidizing (104). A non-volatile intermediate carbon phase exhibiting the Raman spectral features of poorly ordered graphite was formed as the system evolves toward equilibrium as a function of run duration. The thermometric empirical expressions using the G and D bands in the spectra of graphite failed to accurately estimate the experimental temperature. Thus, the existing Raman geothermometers appear inadequate to address graphite formation under conditions of metastable equilibria and to account for kinetic effects such as, for example, the degree of crystallinity. The presence of poorly ordered graphitic carbon at all the redox conditions investigated suggests that the disordered structure of the mineral attains an extensive thermodynamic stability field, and that it may be more readily deposited than crystalline graphite. Metastable graphitic carbon could, therefore, function as a precursor and substrate for the formation of the well-ordered phase. Such metastable graphite may provide an intermediate state that facilitates subduction of carbonaceous material, while imposing constraints on the formation mechanisms and the 13C/12C isotopic systematics of deep seated carbonaceous fluids and minerals such as diamonds. [ABSTRACT FROM AUTHOR]

Abstract: A series of experiments has been conducted in the H2–D2–D2O–H2O–Ti–TiO2 system at temperatures ranging from 300 to 800°C and pressures between ∼0.3 and 1.3GPa in a hydrothermal diamond anvil cell, utilizing Raman spectroscopy as a quantitative tool to explore the relative distribution of hydrogen and deuterium isotopologues of the H2 and H2O in supercritical fluids. In detail, H2O–D2O solutions (1:1) were reacted with Ti metal (3–9h) in the diamond cell, leading to formation of H2, D2, HD, and HDO species through Ti oxidation and H–D isotope exchange reactions. Experimental results obtained in situ and at ambient conditions on quenched samples indicate significant differences from the theoretical estimates of the equilibrium thermodynamic properties of the H–D exchange reactions. In fact, the estimated enthalpy for the H2(aq)–D2(aq) disproportionation reaction (ΔH rxn) is about −3.4kcal/mol, which differs greatly from the +0.16kcal/mol predicted for the exchange reaction in the gas phase by statistical mechanics models. The exothermic behavior of the exchange reaction implies enhanced stability of H2 and D2 relative to HD. Accordingly, the significant energy difference of the internal H2(aq)–D2(aq)–HD(aq) equilibrium translates to strong differences of the fractionation effects between the H2O–H2 and D2O–D2 isotope exchange relationships. The D/H fractionation factors between H2O–H2(aq) and D2O–D2(aq) differ by 365‰ in the 600–800°C temperature range, and are indicative of the greater effect of D2O contribution to the δD isotopic composition of supercritical fluids. The negative ΔH rxn values for the H2(aq)–D2(aq)–HD(aq) equilibrium and the apparent decrease of the equilibrium constant with increasing temperature might be because of differences of the Henry’s law constant between the H- and D-bearing species dissolved in supercritical aqueous solutions. Such effects may be attributed to the stronger hydrogen bonding in the O–H⋯O relative to the O–D⋯O environment. This difference allows enhanced gas solubility in the denser and more polar H2O clusters, and thus, affects the D/H exchange between the H2–D2 volatiles and the coexisting H2O–D2O mixtures. The proposed role of temperature in promoting differences in the density and polarity of hydrogen-bonded OHO and ODO molecules may be explained with isotope-specific molar volume effects similar to those suggested to account for the hydrogen isotope fractionation between H2O and hydroxide mineral phases (e.g. brucite) across large pressure intervals. [Copyright &y& Elsevier]

Abstract: Hydrothermal experiments were conducted to evaluate the kinetics of H2(aq) oxidation in the homogeneous H2–O2–H2O system at conditions reflecting subsurface/near-seafloor hydrothermal environments (55–250°C and 242–497bar). The kinetics of the water-forming reaction that controls the fundamental equilibrium between dissolved H2(aq) and O2(aq), are expected to impose significant constraints on the redox gradients that develop when mixing occurs between oxygenated seawater and high-temperature anoxic vent fluid at near-seafloor conditions. Experimental data indicate that, indeed, the kinetics of H2(aq)–O2(aq) equilibrium become slower with decreasing temperature, allowing excess H2(aq) to remain in solution. Sluggish reaction rates of H2(aq) oxidation suggest that active microbial populations in near-seafloor and subsurface environments could potentially utilize both H2(aq) and O2(aq), even at temperatures lower than 40°C due to H2(aq) persistence in the seawater/vent fluid mixtures. For these H2–O2 disequilibrium conditions, redox gradients along the seawater/hydrothermal fluid mixing interface are not sharp and microbially-mediated H2(aq) oxidation coupled with a lack of other electron acceptors (e.g. nitrate) could provide an important energy source available at low-temperature diffuse flow vent sites. More importantly, when H2(aq)–O2(aq) disequilibrium conditions apply, formation of metastable hydrogen peroxide is observed. The yield of H2O2(aq) synthesis appears to be enhanced under conditions of elevated H2(aq)/O2(aq) molar ratios that correspond to abundant H2(aq) concentrations. Formation of metastable H2O2 is expected to affect the distribution of dissolved organic carbon (DOC) owing to the existence of an additional strong oxidizing agent. Oxidation of magnetite and/or Fe++ by hydrogen peroxide could also induce formation of metastable hydroxyl radicals (•OH) through Fenton-type reactions, further broadening the implications of hydrogen peroxide in hydrothermal environments. [Copyright &y& Elsevier]

Mars has been exposed to ionizing radiation for several billion years, and as part of the search for life on the Red Planet, it is crucial to understand the impact of radiation on biosignature preservation. Several NASA and ESA missions are looking for evidence of ancient life in samples collected at depths shallow enough that they have been impacted by galactic cosmic rays (GCRs). In this study, we exposed a diverse set of Mars analog samples to 0.9 Megagray (MGy) of gamma radiation to mimic 15 million years of exposure on the Martian surface. We measured no significant impact of GCRs on the total organic carbon (TOC) and bulk stable C isotopes in samples with initial TOC concentration > 0.1 wt. %; however, diagnostic molecular biosignatures presented a wide range of degradation that didn't correlate to factors like mineralogy, TOC, water content, and surface area. Exposure dating suggests that the surface of Gale crater has been irradiated at more than five times our dose, yet using this relatively low dose and "best-case scenario" geologically recalcitrant biomarkers, large and variable losses were nevertheless evident. Our results empasize the importance of selecting sampling sites at depth or recently exposed at the Martian surface.

We investigated the impact of pressure on thermophilic, chemolithoautotrophic NO 3 - reducing bacteria of the phyla Campylobacterota and Aquificota isolated from deep-sea hydrothermal vents. Batch incubations at 5 and 20 MPa resulted in decreased NO 3 - consumption, lower cell concentrations, and overall slower growth in Caminibacter mediatlanticus (Campylobacterota) and Thermovibrio ammonificans (Aquificota), relative to batch incubations near standard pressure (0.2 MPa) conditions. Nitrogen isotope fractionation effects from chemolithoautotrophic NO 3 - reduction by both microorganisms were, on the contrary, maintained under all pressure conditions. Comparable chemolithoautotrophic NO 3 - reducing activities between previously reported natural hydrothermal vent fluid microbial communities dominated by Campylobacterota at 25 MPa and Campylobacterota laboratory isolates at 0.2 MPa, suggest robust similarities in cell-specific NO 3 - reduction rates and doubling times between microbial populations and communities growing maximally under similar temperature conditions. Physiological and metabolic comparisons of our results with other studies of pressure effects on anaerobic chemolithoautotrophic processes (i.e., microbial S 0 -oxidation coupled to Fe(III) reduction and hydrogenotrophic methanogenesis) suggest that anaerobic chemolithoautotrophs relying on oxidation-reduction (redox) reactions that yield higher Gibbs energies experience larger shifts in cell-specific respiration rates and doubling times at increased pressures. Overall, our results advance understanding of the role of pressure, its relationship with temperature and redox conditions, and their effects on seafloor chemolithoautotrophic NO 3 - reduction and other anaerobic chemolithoautotrophic processes., (© 2022 John Wiley & Sons Ltd.)