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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]

Fischer-Tropsch type (FTT) synthesis has long been proposed to account for the existence of hydrocarbons in hydrothermal fluids. We show that iron- and chromium-bearing minerals catalyze the abiotic formation of hydrocarbons. In addition to production of methane (C[H.sub.4aq]), we report abiotic generation of ethane ([C.sub.2][H.sub.6aq]) and propane ([C.sub.3][H.sub.8aq]) by mineral-catalyzed hydrothermal reactions at 390°C and 400 bars. Results suggest that the chromium component in ultramafic rocks could be an important factor for FTT synthesis during water-rock interaction in mid-ocean ridge hydrothermal systems. This in turn could help to support microbial communities now recognized in the subsurface at deep-sea vents., Vent fluids issuing from ultramafic-hosted hydrothermal systems at mid-ocean ridges not only contain abundant methane but are also enriched in propane, ethane, and many other dissolved hydrocarbons (1, 2). It [...]

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]