The potential for chemical evolution of complex organic molecules such as peptides in hydrothermal environments requires the persistence of the component amino acids under such conditions. Here, we show experimentally that the redox state (activity of H-2) of the aqueous fluids plays a key role in the stability of glutamic acid during hydrothermal processes. The results demonstrate that highly reducing redox conditions imposed by elevated concentrations of dissolved H-2 suppresses the oxidative decomposition of glutamic acid at elevated temperatures. Our experimental data support proposals that amino acids may persist, albeit metastably, under geochemically relevant hydrothermal conditions. The reduced nature of deep-sea vent fluids might have been a critical parameter in sustaining the needed ingredients for the origin of life on the early Earth, and may currently play a role in facilitating the persistence of biomolecules supporting heterotrophic microbial communities in modern near-seafloor hydrothermal environments. Published by Elsevier B.V.

The effect of pressure and temperature on the structure of silicate melts coexisting with silica-saturated aqueous electrolyte fluids enriched in fluorine or chlorine in the Na2O-Al2O3-SiO2-H2O system has been described. In situ measurements were conducted with the samples at desired temperatures and pressures in a hydrothermal diamond-anvil cell (HDAC) by using microRaman and FTIR spectroscopy techniques. The data were acquired at temperatures and pressures up to 800 degrees C and 1264 MPa, respectively.

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 degrees 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 similar to 850 degrees C, 1.5-2 GPa. In the CaCO3-CaO-H2O system, melt was formed at 600-900 degrees 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 CO32-, 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 ReO2- 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.

Awaruite (Ni2Fe to Ni3Fe) is often used to infer fugacity and redox gradients in hydrothermally altered peridotites. However, discrepant petrological and thermodynamic data suggest that the fO(2)-fS(2) stability field of awaruite is not well constrained. In this study, we assess the thermodynamic properties of awaruite and re-evaluate the Fe-Ni-S systematics of hydrothermally altered peridotites. New experimental data indicate that awaruite is stable at higher fO(2) than previously thought, supporting the common occurrence of awaruite in the reaction zone of modern and ancient ultramafic-hosted hydrothermal vent systems. Awaruite is known to catalyze the abiogenic synthesis of methane during active serpentinization, contributing to methanogenesis at modern oceanic hydrothermal systems and potentially on early Earth. The enhanced stability field of awaruite determined here suggests that abiogenic methanogenesis may be active at a broad range of redox conditions.

Hydrated (with D2O and H2O) sodium tetrasilicate glasses, quenched from melts at 1400 degrees C and 1.5 GPa, are studied using H-1, H-2, and Si-29 solid-state nuclear magnetic resonance (NMR) spectroscopy. Whereas D2O and H2O depolymerize the silicate melt to similar degrees, protium and deuterium intramolecular partitioning between different molecular sites within the glasses is very different and exemplified by a strong preferential association of deuterons to sites with short O-D center dot center dot center dot O distances. This preference is independent of total water content and D/H ratio. Substantially different intramolecular D-H partitioning is also observed in a glass with a model hydrous basalt composition. Such large differences in isotope partitioning cannot result from classic equilibrium fractionation because of the high synthesis temperature. Potential kinetic isotope effects are excluded via a slow quench experiment. The apparent fractionation is likely governed by density/molar volume isotope effects, where deuterium prefers sites with smaller molar volume. Large differences in intramolecular site partitioning in melts could lead to significant differences in D-H partitioning between water-saturated melt and exsolved aqueous fluid (where D/H-W,(Melt) not equal D/H-W,(Fluid)) during crystallization of Earth's magma ocean, potentially controlling the D/H content of the Earth's oceans.

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 degrees 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 degrees 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.

A novel thermophilic, anaerobic, mixotrophic bacterium, designated strain MAG-PB1(T), was isolated from a shallow-water hydrothermal vent system in Palaeochori Bay off the coast of the island of Milos, Greece. The cells were Gram-negative, rugose, short rods, approximately 1.0 mu m long and 0.5 mu m wide. Strain MAG-PB1(T) grew at 30-70 degrees C (optimum 60 degrees C), 0-50 g NaCl l(-1) (optimum 15-20 g l(-1)) and pH 5.5-8.0 (optimum pH 6.0). Generation time under optimal conditions was 2.5 h. Optimal growth occurred under chemolithoautotrophic conditions with H-2 as the energy source and CO2 as the carbon source. Fe(III), Mn(IV), arsenate and selenate were used as electron acceptors. Peptone, tryptone, Casamino acids, sucrose, yeast extract, D-fructose, alpha-D-glucose and (-)-D-arabinose also served as electron donors. No growth occurred in the presence of lactate or formate. The G+C content of the genomic DNA was 66.7 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that this organism is closely related to Deferrisoma camini, the first species of a recently described genus in the Deltaproteobacteria. Based on the 16S rRNA gene phylogenetic analysis and on physiological, biochemical and structural characteristics, the strain was found to represent a novel species, for which the name Deferrisoma palaeochoriense sp. nov. is proposed. The type strain is MAG-PB1(T) (=JCM 30394(T)=DSM 29363(T)).

Previous studies of the stoichiometry of thiosulfate oxidation by colorless sulfur bacteria have failed to demonstrate mass balance of sulfur, indicating that unidentified oxidized products must be present. Here the reaction stoichiometry and kinetics under variable pH conditions during the growth of Thiomicrospira thermophila strain EPR85, isolated from diffuse hydrothermal fluids at the East Pacific Rise, is presented. At pH 8.0, thiosulfate was stoichiometrically converted to sulfate. At lower pH, the products of thiosulfate oxidation were extracellular elemental sulfur and sulfate. We were able to replicate previous experiments and identify the missing sulfur as tetrathionate, consistent with previous reports of the activity of thiosulfate dehydrogenase. Tetrathionate was formed under slightly acidic conditions. Genomic DNA from T. thermophila strain EPR85 contains genes homologous to those in the Sox pathway (soxAXYZBCDL), as well as rhodanese and thiosulfate dehydrogenase. No other sulfur oxidizing bacteria containing sox(CD) 2 genes have been reported to produce extracellular elemental sulfur. If the apparent modified Sox pathway we observed in T. thermophila is present in marine Thiobacillus and Thiomicrospira species, production of extracellular elemental sulfur may be biogeochemically important in marine sulfur cycling.

An empirical model has been developed to depict the ionic strength of concentrated NaCl aqueous solutions at high temperatures and pressures. The model adopts the solvation properties of electrolyte-bearing aqueous solutions that link ionic strength with relative permittivity:

A series of hydrothermal diamond anvil cell experiments was conducted to constrain the effect of anions (Cl-, F-) and cations (Mg+2, Na+) on the molecular structure of high temperature/-pressure fluids, and to express the extent of hydration as a function of solute's speciation and concentration at temperatures ranging from 400 to 800 degrees C and pressures of 1.7 to 30.1 kbar. Results reveal that hydrogen-bonding environments for H2O molecules in the first hydration shell of anions evolve from pure O-H center dot center dot center dot O to dynamic mixtures with O-H center dot center dot center dot X- (F-, Cl-). The distribution of the "O-H center dot center dot center dot X-" structures (O-H center dot center dot center dot O, O-H center dot center dot center dot X-) is proportional to the concentration of dissolved anions; strongly dependent, however, on ionic speciation. To this end, the O-H center dot center dot center dot O structures inside the hydration shell of F- are weaker than the O-H center dot center dot center dot Cl- and O-H center dot center dot center dot O in Cl- bearing solutions. On the contrary, cations (Na+, Mg2+) appear to impose a minimal effect on the Raman spectra of the O-H center dot center dot center dot O structures. The thermodynamic stability of "O-H center dot center dot center dot Cl-" environments shows a strong correlation with the activity of H2O, indicative of the localized effect of the C-l electric field that decouples the hydration from the bulk water molecules. The enthalpy change required to rupture these H-bonding environments (Delta HO-H center dot center dot center dot Cl-) provides a measure for the extent of ion hydration and constrains the solvation properties of supercritical electrolyte solutions. For example, the dominant presence of "O-H center dot center dot center dot Cl-" environments lowers the concentration of isolated water dipoles and contributes to the decrease in the dielectric constant of supercritical electrolyte solutions, which in turn, could suppress the solubility of hydrophobic non-polar aqueous species, such as SiO2(aq). (C) 2016 Elsevier B.V. All rights reserved.