Wide Range Of Physicochemical Conditions Research Articles

Isolation and characterization of plant growth-promoting rhizobacteria (PGPR) from eelgrass Zostera marina rhizosphere: implications for bioremediation

Plant growth-promoting rhizobacteria (PGPR) play a crucial role in enhancing plant growth. However, investigations into the presence and function of PGPR in seagrass rhizospheres remain relatively limited. In this study, we isolated 45 strains of PGPR from Zostera marina rhizospheres and assessed their functional attributes. Additionally, we evaluated the performance of these candidate strains under varying environmental conditions, such as temperature, salinity, and pH. Out of the 45 analyzed strains, 6 were found to possess the nifH gene; some strains also exhibited the ability to solubilize inorganic phosphorus, with dissolved phosphorus content ranging widely from 14.6 to 393.9 mg l-1. Eleven strains demonstrated indole-3-acetic acid production, with yields spanning from 16.3 to 42.8 mg l-1. Siderophores and ammoniated proteins were produced by 32 and 20 strains, respectively. Notably, 5 PGPR strains (F65, G84, G85, G86, and I109) displayed multiple growth-promoting properties along with strong adaptability to a wide range of physicochemical conditions. This study highlights the potential reservoir of PGPR in the eelgrass rhizosphere and provides significant implications for utilizing these bacteria to enhance the success rate of restoring degraded seagrass meadows.

Soils of two Antarctic Dry Valleys exhibit unique microbial community structures in response to similar environmental disturbances

BackgroundIsolating the effects of deterministic variables (e.g., physicochemical conditions) on soil microbial communities from those of neutral processes (e.g., dispersal) remains a major challenge in microbial ecology. In this study, we disturbed soil microbial communities of two McMurdo Dry Valleys of Antarctica exhibiting distinct microbial biogeographic patterns, both devoid of aboveground biota and different in macro- and micro-physicochemical conditions. We modified the availability of water, nitrogen, carbon, copper ions, and sodium chloride salts in a laboratory-based experiment and monitored the microbial communities for up to two months. Our aim was to mimic a likely scenario in the near future, in which similar selective pressures will be applied to both valleys. We hypothesized that, given their unique microbial communities, the two valleys would select for different microbial populations when subjected to the same disturbances.ResultsThe two soil microbial communities, subjected to the same disturbances, did not respond similarly as reflected in both 16S rRNA genes and transcripts. Turnover of the two microbial communities showed a contrasting response to the same environmental disturbances and revealed different potentials for adaptation to change. These results suggest that the heterogeneity between these microbial communities, reflected in their strong biogeographic patterns, was maintained even when subjected to the same selective pressure and that the ‘rare biosphere’, at least in these samples, were deeply divergent and did not act as a reservoir for microbiota that enabled convergent responses to change in environmental conditions.ConclusionsOur findings strongly support the occurrence of endemic microbial communities that show a structural resilience to environmental disturbances, spanning a wide range of physicochemical conditions. In the highly arid and nutrient-limited environment of the Dry Valleys, these results provide direct evidence of microbial biogeographic patterns that can shape the communities’ response in the face of future environmental changes.

Extreme thermal stability of the antiGFP nanobody – GFP complex

ObjectiveThe green fluorescent protein (GFP) and its derivatives are widely used in biomedical research. The manipulation of GFP-tagged proteins by GFP-specific binders, e.g. single-domain antibodies (nanobodies), is of increasing significance. It is therefore important to better understand the properties of antiGFP-GFP interaction in order to establish methodological applications. In this work the interaction of superfolder GFP (sfGFP) and its enhancer nanobody (aGFPenh) was characterized further.ResultsPrevious calorimetric experiments demonstrated that the aGFPenh nanobody binds strongly to sfGFP with a nanomolar affinity. Here we show that this interaction results in a substantial structural stabilization of aGFPenh reflected in a significant increase of its melting temperature by almost 30 °C. The thermal stability of the sfGFP-aGFPenh complex is close to 85 °C in the pH range 7.0–8.5. For therapeutic applications thermoresistance is often an essential factor. Our results suggest that methodologies based on GFP-aGFP interaction can be applied under a wide range of physicochemical conditions. The aGFPenh nanobody seems to be suitable for manipulating sfGFP-labeled targets even in extreme thermophilic organisms.

A new and efficient procedure to load bioactive molecules within the human heavy-chain ferritin nanocage.

For their easy and high-yield recombinant production, their high stability in a wide range of physico-chemical conditions and their characteristic hollow structure, ferritins (Fts) are considered useful scaffolds to encapsulate bioactive molecules. Notably, for the absence of immunogenicity and the selective interaction with tumor cells, the nanocages constituted by the heavy chain of the human variant of ferritin (hHFt) are optimal candidates for the delivery of anti-cancer drugs. hHFt nanocages can be disassembled and reassembled in vitro to allow the loading of cargo molecules, however the currently available protocols present some relevant drawbacks. Indeed, protein disassembly is achieved by exposure to extreme pH (either acidic or alkaline), followed by incubation at neutral pH to allow reassembly, but the final protein recovery and homogeneity are not satisfactory. Moreover, the exposure to extreme pH may affect the structure of the molecule to be loaded. In this paper, we report an alternative, efficient and reproducible procedure to reversibly disassemble hHFt under mild pH conditions. We demonstrate that a small amount of sodium dodecyl sulfate (SDS) is sufficient to disassemble the nanocage, which quantitatively reassembles upon SDS removal. Electron microscopy and X-ray crystallography show that the reassembled protein is identical to the untreated one. The newly developed procedure was used to encapsulate two small molecules. When compared to the existing disassembly/reassembly procedures, our approach can be applied in a wide range of pH values and temperatures, is compatible with a larger number of cargos and allows a higher protein recovery.

Successive Modes of Carbonate Precipitation in Microbialites along the Hydrothermal Spring of La Salsa in Laguna Pastos Grandes (Bolivian Altiplano)

Interpreting the paleoecosystems of ancient microbialites relies on our understanding of how modern microbialites form in relation with the bio-physico-chemical conditions of their environment. In this study, we investigated the formation of modern carbonate microbialites in the hydrothermal system of La Salsa in Laguna Pastos Grandes (Bolivia), which spans a wide range of physicochemical conditions and associated microbial communities. By combining dissolved inorganic carbon (DIC) isotope mass balance modeling, analysis of carbonates solubility diagram, and imaging of the microorganisms–mineral assemblages within microbial mats, we found that several modes of carbonate precipitation dominate in distinct portions of the hydrothermal system. (1) In high-[DIC] waters, undersaturated to slightly saturated with respect to calcite, cyanobacterial calcification is promoted by CO2 degassing and photosynthetic activity within the microbial mats. (2) In alkaline waters undergoing sustained evaporation, the precipitation of an amorphous calcium carbonate phase seems to control the water a(Ca2+)/a(CO32−) ratio and to serve as a precursor to micritic calcite formation in microbial mats. (3) In saline ephemeral ponds, where the carbonate precipitation is the highest, calcite precipitation probably occurs through a different pathway, leading to a different calcite texture, i.e., aggregates of rhombohedral crystals.

Understanding the factors affecting adsorption of pharmaceuticals on different adsorbents – A critical literature update

Remediation of emerging pharmaceutically active compounds (PhACs) as micropollutants in wastewater is of foremost importance as they can cause extremely detrimental effects on life upon bioaccumulation and generation of drug-resistance microorganisms. Presently used physicochemical treatments, such as electrochemical oxidation, nanofiltration and reverse osmosis, are not feasible owing to high operating costs, incomplete removal of contaminants along with toxic by-products formation. Adsorption with the utilization of facile and efficient nanoparticulate adsorbents having distinctive properties of high surface area, excellent adsorption capacity, ability to undergo surface engineering and good regeneration displays great potential in this aspect along with the incorporation of nanotechnology for effective treatment. The application of such nanosorbents provides optimal performance under a wide range of physicochemical conditions, decreased secondary pollution with reduced mechanical stress along with excellent organic compound sequestration capacity, which in turn improves the quality of potable water in a sustainable way compared to current treatments. The present review intends to consolidate the range of factors that affect the process of adsorption of different PhACs on to various nanosorbents and also highlights the adsorption mechanism aiding in the retrieval.

Bivalve Molluscs as Model Systems for Studying Mitochondrial Biology.

The class Bivalvia is a highly successful and ancient taxon including ∼25,000 living species. During their long evolutionary history bivalves adapted to a wide range of physicochemical conditions, habitats, biological interactions, and feeding habits. Bivalves can have strikingly different size, and despite their apparently simple body plan, they evolved very different shell shapes, and complex anatomic structures. One of the most striking features of this class of animals is their peculiar mitochondrial biology: some bivalves have facultatively anaerobic mitochondria that allow them to survive prolonged periods of anoxia/hypoxia. Moreover, more than 100 species have now been reported showing the only known evolutionarily stable exception to the strictly maternal inheritance of mitochondria in animals, named doubly uniparental inheritance. Mitochondrial activity is fundamental to eukaryotic life, and thanks to their diversity and uncommon features, bivalves represent a great model system to expand our knowledge about mitochondrial biology, so far limited to a few species. We highlight recent works studying mitochondrial biology in bivalves at either genomic or physiological level. A link between these two approaches is still missing, and we believe that an integrated approach and collaborative relationships are the only possible ways to be successful in such endeavor.

Experimental investigation of the reactions between pyrite and aqueous Cu(I) chloride solution at 100–250 °C

Replacement of pyrite by copper-bearing sulfides is widespread in mineral deposits, with zonation of chalcocite, bornite, and chalcopyrite being a common result of this process. Copper occurs predominantly as Cu(I) in hydrothermal fluids, but the mechanistic details of reactions between pyrite and aqueous Cu(I) and their relevance to the zonation of Cu sulfides in hydrothermal deposits remain poorly understood, because of a lack of relevant experimental constraints. In this study, we investigated the reactions between pyrite and aqueous Cu(I) chloride solutions over a wide range of physicochemical conditions (100–250 °C; pH = 1–8; saturated vapor pressure). The experimental results show that Cu-bearing sulfides form at temperatures of >150 °C, and that pH exerts an important control on the mineralogy of the reaction products. In strongly acidic conditions (pH = 1.1), pyrite dissolution occurs; in acidic-to-neutral conditions (pH = 3.0–6.0), chalcopyrite and bornite are the main products; in weakly alkaline conditions (pH = 8.2), the replacement products are chalcocite and bornite. Chalcopyrite, bornite, and chalcocite generally occur in a zoned sequence outward from the pyrite reaction front to the bulk solution, and the replacement of pyrite by chalcopyrite is heterogeneous. In situ Raman observation and S isotope analyses suggest that pyrite replacement by chalcopyrite is a redox-coupled dissolution–precipitation reaction, with the oxidative dissolution of pyrite to form sulfate, generating the electrons that maintain the reductive replacement of pyrite by chalcopyrite. The sites of oxidative dissolution and reductive replacement can be spatially separated, but coupled by electron transfer. By contrast, the further replacement of chalcopyrite by bornite and chalcocite does not involve the oxidative dissolution of sulfur, but release of iron and H+, which could be promoted at higher pH. Notably, when the zonation of sulfides is established in a hydrothermal experiment of pyrite replacement by Cu(I) solution, gradients of H2S (or HS–), Cu(I), and Fe(II) are developed between the pyrite reaction front and bulk solution via diffusion through interstitial pore space. As such, the inner zones of chalcopyrite and bornite are not in equilibrium with the bulk solution as confirmed by thermodynamic calculations. The results imply that the zonation of Cu-bearing sulfides in mineral deposits records heterogeneous chemical environments, from the mineral interface- to the ore deposit-scale during dynamic mineralization processes.

Paleoenvironmental control on trace fossils across a Mississippian carbonate ramp succession, Mobarak Formation, east of Central and Eastern Alborz, Iran

The Lower Carboniferous Mobarak Formation in the east of Central and Eastern Alborz Mountains, northern Iran, is deposited on a distally steepened carbonate ramp. Detailed facies analysis allowed to differentiate seven facies associations, includes deep marine basinal (FA1), toe-of-slope/outer ramp (FA2), ramp/slope (FA3), shallow open marine (FA4), bioclastic bars or shoal (FA5), lagoon (FA6) and intertidal flat (FA7). The trace-fossil suites of the studied successions are shown for the first time. Twenty eight ichnogenera were identified, i.e. Arenicolites, Asterosoma, Bergaueria, Chondrites, Cochlichnus, Diplocraterion, Halopoa, Helminthopsis, Helminthorhaphe?, Helminthoidichnites, Gordia, Gyrochorte, Lockeia, Mammilichnis, Megagrapton, Nereites?, Palaeophycus, Phycodes, Phycosiphon, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Sinusichnus, Skolithos, Taenidium, Thalassinoides, and Zoophycos. The seven facies associations deposited in a wide range of physico-chemical conditions, show distinct proximal to distal trends. As a result of oxygen-depleted depositional conditions, only the tracemakers of Zoophycos survived in deep marine slopes, which were close to turbiditic sedimentation zones. The development of a benthic community under the stable condition and a long-term colonization window were documented by highly diverse suites of the Cruziana ichnofacies. Under a stressed environment (after tempestite deposition), the Skolithos ichnofacies displayed a low diversity of opportunistic ichnocommunity suite. The mixed Skolithos–Cruziana ichnofacies occur in the middle to distal lower inner ramp. The identification of the archetypal ichnofacies may document broad changes of environmental parameters such as variability in sedimentation rates, energy level, salinity, substrate properties/consistency, nature of nutrient supply and dissolved oxygen content. Relationships among different modes of ethology of tracemakers and sedimentary structures in the studied successions are used to clarify sedimentary conditions.

Estuarine Macrofauna Affects Benthic Biogeochemistry in a Hypertrophic Lagoon

Coastal lagoons display a wide range of physico-chemical conditions that shape benthic macrofauna communities. In turn, benthic macrofauna affects a wide array of biogeochemical processes as a consequence of feeding, bioirrigation, ventilation, and excretion activities. In this work, we have measured benthic respiration and solute fluxes in intact sediment cores with natural macrofauna communities collected from four distinct areas within the Sacca di Goro Lagoon (NE Adriatic Sea). The macrofauna community was characterized at the end of the incubations. Redundancy analysis (RDA) was used to quantify and test the interactions between the dominant macrofauna species and solute fluxes. Moreover, the relevance of macrofauna as driver of benthic nitrogen (N) redundancy analysis revealed that up to 66% of the benthic fluxes and metabolism variance was explained by macrofauna microbial-mediated N processes. Nitrification was stimulated by the presence of shallow (corophiids) in combination with deep burrowers (spionids, oligochaetes) or ammonium-excreting clams. Deep burrowers and clams increase ammonium availability in burrows actively ventilated by corophiids, which creates optimal conditions to nitrifiers. However, the stimulatory effect of burrowing macrofauna on nitrification does not necessarily result in higher denitrification as processes are spatially separated.

Modeling of Nanoparticle-Stabilized CO2 Foam Enhanced Oil Recovery

Summary Previous experimental studies show that “nanoparticle-stabilized” supercritical carbon dioxide (CO2) foams (NP-stabilized CO2 foams or NP CO2 foams in this paper) can be applied as an alternative to surfactant foams, to reduce CO2 mobility in gas-injection enhanced oil recovery (EOR). The NPs, if chosen correctly, can be effective foam stabilizers attached at the fluid interface in a wide range of physicochemical conditions. By using NP CO2 foam experiments available in the literature, this study investigates the applicability of NP foams for mobility control and, thus, improved sweep efficiency. This study consists of two tasks: (1) presenting how a population-balance mechanistic foam model can be used to fit experimental data and determine required model parameters and (2) examining sweep efficiency in a condition resembling Lisama Field (a five-spot pattern with four producers and one injector in the middle), by using relevant gas mobility-reduction factors (MRFs) derived from the mechanistic-modeling technique. The field-scale simulations are conducted with Computer Modeling Group (CMG) software, contrasting NP and surfactant foams (in both dry and wet foam-injection conditions) to a gas-only injection and a gas/water coinjection (no foam). The results show how the model can successfully reproduce coreflood experimental data, creating three different foam states (weak foam, strong foam, and intermediate) and two steady-state strong-foam regimes (high quality and low quality). When the gas-phase MRFs, ranging up to 10 from the model fit, are applied in the field-scale simulations, the use of NPs improves oil recovery compared with a gas/water coinjection, but not as efficiently as a successful surfactant foam injection does. This implies that, although NP-stabilized foams do provide some benefits, there still seems to be some room to improve the stability and the strength of resulting foams.

Water level fluctuations and phenological responses in a salt marsh succulent

The succulent salt marsh plant Salicornia tegetaria occurs in both temporarily open / closed (TOCE) and permanently open estuaries (POE) where it experiences a wide range of physicochemical conditions in South African estuaries. The study investigated the characteristics of this plant in relation to water level in a TOCE and a POE and showed that cover was stable in the permanently open estuary but changed in response in water level in the temporarily open/closed system. Monthly expansion in S. tegetaria cover was 46% compared to 5.2% in the POE. In the TOCE the life cycle took four months to complete, seedlings emerged two days after the water level dropped, and the habitat was exposed. This was despite the mouth being closed for the whole study period and a mean water depth inundation of 27 ± 6 cm. Plants in the TOCE produced significantly more inflorescences (409 ± 79 per m²) and seed (45 542 ± 9 212 per m2), compared to the plants in the POE where water level was stable (87 ± 9 inflorescences per m² and 7 092 ± 775 seeds per m²). A large sediment seedbank (9 758 seeds m−2) in the TOCE ensures germination when water level drops and conditions become favourable for establishment. These data are important as they indicate that S. tegetaria is a remarkably adaptive species that can grow over a wide range of physicochemical conditions that will allow the species to persist in the face of future future sea level rise and anthropogenic pressures.

Vertical and horizontal assemblage patterns of bacterial communities in a eutrophic river receiving domestic wastewater in southeast China

Bacterial communities in rivers receiving untreated domestic wastewater may show specific spatial assemblage patterns due to a wide range of physicochemical conditions created by periodic algal bloom. However, there are significant gaps in understanding environmental forces that drive changes in microbial assemblages in polluted rivers. In this study, we applied high-throughput sequencing of 16S rRNA gene amplicons to perform comprehensive spatio-temporal profiling of bacterial community structure in a local river segment receiving domestic wastewater discharge in southeast China. Multivariate statistics were then used to analyse links between bacterial community structure and environmental factors. Non-metric multidimensional scaling (NMDS) plots showed that the bacterial community structure was different between upstream and downstream sections of the river. While the upstream water contained a high proportion of bacteria degrading xenobiotic aromatic compounds, the downstream water experiencing stronger algal bloom had a more diverse bacterial community which included the genus Aeromonas comprising 14 species, most of which are human pathogens. Least discriminant analysis (LDA) effect size revealed that the surface water was mainly inhabited by aerobic microorganisms capable of degrading aromatic compounds, and also contained bacterial genera including pathogenic species. In contrast, in the bottom water we found, along with aromatic compound-degrading species, anaerobic denitrifiers and Fe3+-reducing and fermentative bacteria. Variance partitioning canonical correspondence analysis (VPA) showed that nutrient ratios had a stronger contribution to bacterial dissimilarities than other major physicochemical factors (temperature, pH, dissolved oxygen, total organic carbon, and chlorophyll a). These results show that microbial communities in rivers continuously receiving domestic wastewater have specific longitudinal and vertical assemblage patterns and may contain pathogenic species presenting a high threat to public health. These factors should be taken into consideration while developing pollution management strategies.

Presencia de Legionella spp. en depósitos domiciliarios de agua potable en Resistencia, Chaco, Argentina. Informe preliminar

Legionella spp. is an environmental bacterium that can survive in a wide range of physicochemical conditions and may colonize distribution systems of drinking water and storage tanks. Legionella pneumophila is the major waterborne pathogen that can cause 90% of Legionnaires’ disease cases. The aim of this study was to detect the presence of Legionella spp. in household drinking water tanks in the city of Resistencia, Chaco. The detection of Legionella in water samples was performed by culture methods as set out in ISO 11731:1998. Thirty two water samples were analyzed and Legionella spp. was recovered in 12 (37.5%) of them. The monitoring of this microorganism in drinking water is the first step towards addressing the control of its spread to susceptible hosts.

The coupled geochemistry of Au and As in pyrite from hydrothermal ore deposits

The ubiquity of Au-bearing arsenian pyrite in hydrothermal ore deposits suggests that the coupled geochemical behaviour of Au and As in this sulfide occurs under a wide range of physico-chemical conditions. Despite significant advances in the last 20years, fundamental factors controlling Au and As ratios in pyrite from ore deposits remain poorly known. Here we explore these constraints using new and previously published EMPA, LA-ICP-MS, SIMS, and μ-PIXE analyses of As and Au in pyrite from Carlin-type Au, epithermal Au, porphyry Cu, Cu–Au, and orogenic Au deposits, volcanogenic massive sulfide (VHMS), Witwatersrand Au, iron oxide copper gold (IOCG), and coal deposits. Pyrite included in the data compilation formed under temperatures from ∼30 to ∼600°C and in a wide variety of geological environments. The pyrite Au-As data form a wedge-shaped zone in compositional space, and the fact that most data points plot below the solid solubility limit defined by Reich et al. (2005) indicate that Au1+ is the dominant form of Au in arsenian pyrite and that Au-bearing ore fluids that deposit this sulfide are mostly undersaturated with respect to native Au. The analytical data also show that the solid solubility limit of Au in arsenian pyrite defined by an Au/As ratio of 0.02 is independent of the geochemical environment of pyrite formation and rather depends on the crystal-chemical properties of pyrite and post-depositional alteration. Compilation of Au–As concentrations and formation temperatures for pyrite indicates that Au and As solubility in pyrite is retrograde; Au and As contents decrease as a function of increasing temperature from ∼200 to ∼500°C. Based on these results, two major Au–As trends for Au-bearing arsenian pyrite from ore deposits are defined. One trend is formed by pyrites from Carlin-type and orogenic Au deposits where compositions are largely controlled by fluid-rock interactions and/or can be highly perturbed by changes in temperature and alteration by hydrothermal fluids. The second trend consists of pyrites from porphyry Cu and epithermal Au deposits, which are characterised by compositions that preserve the Au/As signature of mineralizing magmatic-hydrothermal fluids, confirming the role of this sulfide in controlling metal ratios in ore systems.

Characterization of mercury sorption on hydroxylapatite: Batch studies and microscopic evidence for adsorption

Although previous studies have investigated Hg sorption on various common minerals, there has been limited study of Hg interaction with apatite. In this study, systematic experiments regarding Hg sorption on HAP were performed over a wide range of physicochemical conditions. In the sorption edge experiments, Hg uptake by HAP exhibits a maximum sorption (∼90%) at pH 6.0, which rapidly decreases at pH>6.0. Sorption isotherms are fitted well by Freundlich equations, and the distribution coefficient (KD) increases in the order of pH 5>7>9. In both the sorption edge and isotherm experiments, sorption patterns and quantities are minimally influenced by variations in the ionic strength. The results from the kinetic experiments are in good agreement with the pseudo-second-order rate law. The initial sorption rate at pH 9 is much slower than that at pH 5 and 7. During desorption, ∼90% of the sorbed Hg is retained at both pH 6.0 and 9.0, which indicates strong bonding of Hg to the HAP surface. Our results suggest that adsorption plays an important role in controlling the initial stage of interactions between Hg and HAP.

The effects of temperature, pH and redox state on the stability of glutamic acid in hydrothermal fluids

Natural hydrothermal vent environments cover a wide range of physicochemical conditions involving temperature, pH and redox state. The stability of simple biomolecules such as amino acids in such environments is of interest in various fields of study from the origin of life to the metabolism of microbes at the present day. Numerous previous experimental studies have suggested that amino acids are unstable under hydrothermal conditions and decompose rapidly. However, previous studies have not effectively controlled the redox state of the hydrothermal fluids. Here we studied the stability of glutamate with and without reducing hydrothermal conditions imposed by 13mM aqueous H2 at temperatures of 150, 200 and 250°C and initial (25°C) pH values of 6 and 10 in a flow-through hydrothermal reactor with reaction times from 3 to 36min. We combined the experimental measurements with theoretical calculations to model the in situ aqueous speciation and pH values. As previously observed under hydrothermal conditions, the main reaction involves glutamate cyclizing to pyroglutamate through a simple dehydration reaction. However, the amounts of decomposition products of the glutamate detected, including succinate, formate, carbon dioxide and ammonia depend on the temperature, the pH and particularly the redox state of the fluid. In the absence of dissolved H2, glutamate decomposes in the sequence glutamate, glutaconate, α-hydroxyglutarate, ketoglutarate, formate and succinate, and ultimately to CO2 and micromolar quantities of H2(aq). Model speciation calculations indicate the CO2, formate and H2(aq) are not in metastable thermodynamic equilibrium. However, with 13mM H2(aq) concentrations, the amounts of decomposition products are suppressed at all temperatures and pH values investigated. The small amounts of CO2 and formate present are calculated to be in metastable equilibrium with the H2. It is further proposed that there is a metastable equilibrium between glutamate, glutaconate, α-hydroxyglutarate, ketoglutarate and H2. The key redox-sensitive step is the reaction of α-hydroxyglutarate to α-ketoglutarate, which is effectively inhibited by the elevated H2 concentrations, which in turn dramatically lowers the amounts of all decomposition products including ammonia. Theoretical calculations of the metastable thermodynamic equilibrium between glutamate and ketoglutarate are consistent with the experimentally determined effects of reducing conditions. These findings establish that redox state is as important a variable as temperature and pH in affecting the stability of amino acids under hydrothermal conditions. It is suggested that when natural hydrothermal fluids contain enough dissolved H2, the stability of amino acids may be enhanced in fluids at least on short time scales. In turn, this result suggests that reducing hydrothermal environments may have been favorable for assembling the building blocks of biomolecules in the origin of life. Furthermore, in present day hydrothermal vents the microbial ecosystems may in part be supported by the availability of metastable amino acids through heterotrophic metabolism.

Designing small-molecule catalysts for CO2 capture

One method for CO2 capture is to dissolve CO2 in water to form carbonic acid. This reaction (CO2+H20→H2CO3(aq)) is remarkably slow but is catalyzed in biological systems by an enzyme called carbonic anhydrase (CA). The catalyzed reaction is diffusion limited and occurs at near neutral pH. The enzyme catalytic center is composed of a Zn(II) ion that is coordinated by 3 histidine residues and an axial water/hydroxyl group. A nucleophilic attack by the hydroxyl group on the CO2 molecule is the first step in the reaction mechanism. Cu(II), Hg(II), Cd(II), Ni(II), Co(II) and Mn(II) can bind the CA binding site and substitute the zinc ion; however, only Co(II) yields rates comparable to Zn(II). Unfortunately, an enzyme, such as carbonic anhydrase, is not amenable for industrial applications where a wide range of physico-chemical conditions exist. Enzymes are vulnerable to large pressures, high temperature, and high ionic strength. Efforts to isolate the key structural features responsible for catalysis led to the development of small-molecule mimetics of the CA catalytic site. These mimetics can, in turn, be used as catalyst for CO2 sequestration. Two of the fastest catalyst are the cyclic molecules: 1, 4, 7, 10-tetraazacyclododedacane and 1, 5, 9-triazacyclododedacane (both complexed with a Zn(II) ion). Nitrogen atoms in these cyclic molecules mimic the imidazole nitrogens of the CA active site. It is possible to examine the energetics of these compounds using transition state theory for the purposes of designing more efficient catalysts. Transition state theory predicts that the reaction rate constant is proportional to exp(−Ea/kT), where Ea denotes the activation energy, k the Boltzmann constant, and T the temperature of the reaction. The activation energy is the energetic cost of forming the reaction transition state from the reactants. Ab initio calculations can yield the activation energy, which can, in principle, be used as a design metric for more efficient catalysts. Using this approach, the difference in kinetic rate constant between the tetra- and tri-aza dodecane catalysts can be determined. Furthermore, the rates of the corresponding Co(II) catalysts were explored. Our data suggests this is a viable method for the design of inorganic small-molecule catalysts.

Diversity of Meiofauna from the 9°50′N East Pacific Rise across a Gradient of Hydrothermal Fluid Emissions

BackgroundWe studied the meiofauna community at deep-sea hydrothermal vents along a gradient of vent fluid emissions in the axial summit trought (AST) of the East Pacific Rise 9°50′N region. The gradient ranged from extreme high temperatures, high sulfide concentrations, and low pH at sulfide chimneys to ambient deep-sea water conditions on bare basalt. We explore meiofauna diversity and abundance, and discuss its possible underlying ecological and evolutionary processes.Methodology/Principal FindingsAfter sampling in five physico-chemically different habitats, the meiofauna was sorted, counted and classified. Abundances were low at all sites. A total of 52 species were identified at vent habitats. The vent community was dominated by hard substrate generalists that also lived on bare basalt at ambient deep-sea temperature in the axial summit trough (AST generalists). Some vent species were restricted to a specific vent habitat (vent specialists), but others occurred over a wide range of physico-chemical conditions (vent generalists). Additionally, 35 species were only found on cold bare basalt (basalt specialists). At vent sites, species richness and diversity clearly increased with decreasing influence of vent fluid emissions from extreme flow sulfide chimney (no fauna), high flow pompei worm (S: 4–7, H'loge: 0.11–0.45), vigorous flow tubeworm (S: 8–23; H'loge: 0.44–2.00) to low flow mussel habitats (S: 28–31; H'loge: 2.34–2.60).Conclusions/SignificanceOur data suggest that with increasing temperature and toxic hydrogen sulfide concentrations and increasing amplitude of variation of these factors, fewer species are able to cope with these extreme conditions. This results in less diverse communities in more extreme habitats. The finding of many species being present at sites with and without vent fluid emissions points to a non endemic deep-sea hydrothermal vent meiofaunal community. This is in contrast to a mostly endemic macrofauna but similar to what is known for meiofauna from shallow-water vents.

A thermodynamic model for titanium and ferric iron solution in biotite

AbstractRecent crystallographic data indicate that in biotite Ti orders preferentially onto the M2 octahedral site rather than onto the M1 site as assumed in previous solution models for K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (KFMASHTO) biotite. In view of these data, we reformulate and reparameterize former biotite solution models. Our reparameterization takes into account Fe–Mg order–disorder and ferric iron contents of natural biotite as well as both natural and experimental observations on biotite Ti‐content over a wide range of physicochemical conditions. In comparison with previous biotite models, the new model reproduces the Ti‐content and stability field of biotite as constrained by experiments with significantly better accuracy. The predictive power of the model is tested by comparison with petrologically well‐characterized natural samples of SiO2‐saturated and SiO2‐undersaturated rocks that were not used in the parameterization. In all these tests, the reformulated model performs well.