Dissolved inorganic carbon accumulating complexes from autotrophic bacteria from extreme environments

In nature, concentrations of dissolved inorganic carbon (DIC; = CO 2 + HCO 3 - + CO 3 2- ) can be low, and autotrophic organisms adapt with a variety of mechanisms to elevate intracellular DIC concentrations to enhance CO 2 fixation. Such mechanisms have been well-studied in Cyanobacteria , but much remains to be learned about their activity in other phyla. Novel multi-subunit membrane-spanning complexes capable of elevating intracellular DIC were recently described in three species of bacteria. Homologs of these complexes are distributed among 17 phyla in Bacteria and Archaea, and are predicted to consist of one, two, or three subunits. To determine whether DIC accumulation is a shared feature of these diverse complexes, seven of them, representative of organisms from four phyla, from a variety of habitats, and with three different subunit configurations were chosen for study. A high-CO 2 requiring, carbonic anhydrase-deficient ( yadF - cynT - ) strain of E. coli Lemo21(DE3), which could be rescued via elevated intracellular DIC concentrations, was created for heterologous expression and characterization of the complexes. Expression of all seven complexes rescued the ability of E. coli Lemo21(DE3) yadF - cynT - to grow under low CO 2 conditions, and six of the seven generated measurably elevated intracellular DIC concentrations when their expression was induced. For complexes consisting of two or three subunits, all subunits were necessary for DIC accumulation. Isotopic disequilibrium experiments clarified that CO 2 was the substrate for these complexes. In addition, the presence of an ionophore prevented the accumulation of intracellular DIC, suggesting that these complexes may couple proton potential to DIC accumulation. IMPORTANCE To facilitate the synthesis of biomass from CO 2 , autotrophic organisms use a variety of mechanisms to increase intracellular DIC concentrations. A novel type of multi-subunit complex has recently been described, which has been shown to generate measurably elevated intracellular DIC concentrations in three species of bacteria, begging the question of whether these complexes share this capability across the 17 phyla of Bacteria and Archaea where they are found. This study shows that DIC accumulation is a trait shared by complexes with varied subunit structures, from organisms with diverse physiologies and taxonomies, suggesting that this trait is universal among them. Successful expression in E. coli suggests the possibility of their expression in engineered organisms synthesizing compounds of industrial importance from CO 2 .

Progress and pitfalls in dating deformation with carbonate geochronology

<p>Several isotopic systems can potentially be used to provide absolute chronology of carbonate minerals; these include Rb-Sr, Sm-Nd, U-Pb and U-Th. The production of a robust date requires incorporation of the parent isotope during formation, and ideally low abundance of the daughter isotope. Variable parent-daughter (P/D) abundance during formation additionally can increase the robustness of the resulting isochron. The ability to use high spatial resolution sampling via laser ablation (LA-) ICP-MS, makes it the most attractive technique, as varying P/D ratios can be sampled within single age domains, whether these be crystals, growth bands, or other textural domains. Of the systems available in carbonate, U-Pb is the only one that is commonly applied with LA-ICP-MS methods, although the others are all possible with modern instrumentation. Of note, collision-cell technology means that Rb-Sr is regaining popularity as an in situ dating method. Carbonate geochronology can be achieved at a range of timescales, with U-Th ranging from 100s yrs to ca. 500 ka, and U-Pb ranging from 100s ka to 100s Ma. The potential for isotopic disequilibrium effecting measured U-Pb ages, means that young (< 10 Ma) U-Pb dates are susceptible to inaccuracy. Published LA-ICP-MS U-Pb dates suggest that this method can be pushed well into the Precambrian.</p><p> </p><p>The application of U-Th and U-Pb geochronology to provide direct timing constraints on deformation gained ground around 10 and 5 years ago, respectively. Because LA-ICP-MS instrumentation is relatively common, and because ancient carbonates provide undated material of significant interest, U-Pb in particular has become a rapidly growing technique. The biggest advance in LA-ICP-MS U-Pb dating has been the characterisation of matrix-matched calcite reference materials (RMs). The observation of minor matrix-related effects between carbonate matrices however, means that the availability of well characterised RMs for minerals such as dolomite and siderite, are a limiting factor in the accuracy of these non-calcite dates. In terms of deformation, most existing data corresponds to calcite.</p><p> </p><p>Calcite precipitates from fluid at a range of temperatures in the upper crust, with fluid-flow typically being enhanced by brittle deformation, i.e. faulting and fracturing. To link calcite dates to the timing of specific deformational events, such as fault slip or fracture-opening, various ‘syn-tectonic’ or ‘syn-kinematic’ vein types have ben utilised. These include slickenfibres, breccia cements, and various types of vein arrays. Each of these structures has variable ability to faithfully record the timing of fault slip, and the ability to link calcite mineralisation to the timing of fault slip remains one of the most assumptive parts of this method. Detailed petrographic and compositional characterisation and documentation are required, for which a range of methods are available, such as cathodoluminescence and trace element mapping. Along with a summary of the advances in carbonate geochronology, various examples of vein structures and of methods for characterisation will be discussed, including examples where there is evidence for overprinting by later fluid-flow.</p>

Petrogenesis of the Nashwaak Granite, West-Central New Brunswick, Canada: Evidence from Trace Elements, O and Hf Isotopes of Zircon, and O Isotopes of Quartz

The petrogenesis of the Pridoli to Early Lochkovian granites in the Miramichi Highlands of New Brunswick, Canada, is controversial. This study focuses on the Pridoli Nashwaak Granite (biotite granite and two-mica granite). In situ trace elements and O and Hf isotopes in zircon, coupled with O isotopes in quartz, are used to reveal its magmatic sources and evolution processes. In the biotite granite, inherited zircon cores have broadly homogenous δ18OZrc ranging from +6.7‰ to 7.4‰, whereas magmatic zircon rims have δ18OZrc of +6.3‰ to 7.2‰ and εHf(t) of −0.39 to −5.10. The Hf and Yb/Gd increase with decreasing Th/U. Quartz is isotopically equilibrated with magmatic zircon rims. The biotite granite is interpreted to be solely derived by partial melting of old basement rocks of Ganderia and fractionally crystallized at the fO2 of 10−21 to 10−10 bars. The two-mica granite has heterogeneous inherited zircon cores (δ18OZrc of +5.2‰ to 9.9‰) and rims (δ18OZrc of +6.2‰ to 8.7‰), and εHf(t) of −11.7 to −1.01. The two-mica granite was derived from the same basement, but with supracrustal contamination. This open-system process is also recorded by Yb/Gd and Th/U ratios in zircon and isotopic disequilibrium between magmatic zircon rims and quartz (+10.3 ± 0.2‰).

Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium

Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate precipitation occurs in isotopic disequilibrium. To date, knowledge of these common isotopic disequilibria, known as vital effects in biogenic carbonates, remains limited, and the potential information recorded by δ18O and Δ47 offsets from isotopic equilibrium values is largely overlooked. Additionally, in carbonates formed in isotopic equilibrium, the use of the carbonate δ18O signature as a paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰), measured on microbial carbonates that are strongly linked to carbonate δ18O offsets (−25 ‰) from equilibrium. These offsets are likely both related to the microorganism metabolic activity and yield identical erroneous temperature reconstructions. Unexpectedly, we show that the δ18O value of the water in which carbonates precipitated, as well as the water–carbonate δ18O fractionation dependence on temperature at equilibrium, can be retrieved from these paired δ18O and Δ47 disequilibrium values measured in carbonates. The possibility to retrieve the δ18O value of paleowaters, sediments' interstitial waters or organisms' body water at the carbonate precipitation loci, even from carbonates formed in isotopic disequilibrium, opens long-awaited research avenues for both paleoenvironmental reconstructions and biomineralization studies.

Solution to an enigma: Explaining the slope of carbon vs. oxygen isotopic disequilibrium in biogenic and inorganic carbonates

<p>A widespread phenomenon in biogenic and inorganic carbonates that are formed out of isotopic equilibrium is a nearly ubiquitous co-variation (slope) of carbon vs. oxygen isotopes, in e.g., speleothem and cryogenic carbonates, shells and skeletons of foraminifera, corals etc. For proxy calibrations, it is critical to understand such isotope variations (often labeled kinetic or vital effects) in proxies widely used for paleo-reconstructions. Given that this phenomenon is observed in inorganic carbonates and biogenic carbonates across different phyla suggest a common underlying mechanism, possibly independent of biological controls, that is, likely of inorganic origin. Here we present results from laboratory experiments on synthetic carbonate precipitation to constrain the kinetic isotope fractionation factor (KFF) of carbon and oxygen during CO2 hydration. We used an experimental setup similar to that of an earlier study but with important modifications and tight temperature and pH control. The average d13C and d18O values of our carbonate samples (BaCO3) produced at 25 deg C and pH = 8.0 (NBS) are -29.7 +- 0.71 per mil (VPDB) and 18.8 +- 0.56 per mil (VSMOW), respectively. From the isotope data, we calculate our experimental 13KFF and 18KFF, which refer to the 13C/12C and 18O/16O fractionation between CO2(g) and BaCO3, where the d13C and d18O values of CO2(g) were calculated using known equilibrium fractionation factors. Our results show that our KFFs are the largest values compared to previously reported experimental KFFs (except for one study), suggesting that our values are closest to the full isotopic disequilibrium during CO2 hydration. Based on our KFFs, we will present the expected slope of carbon vs. oxygen isotopic disequilibrium from kinetic effects during CO2 hydration. We will also discuss the expected slope from equilibrium effects of solution pH on oxygen isotopes. Comparison with field and culture data will reveal the origin of the slope of carbon vs. oxygen isotopic disequilibrium in biogenic and inorganic carbonates.</p>

Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium

Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate crystallization occurs in isotopic disequilibrium. To date, knowledge of these common isotopic disequilibria, known as vital effects in biogenic carbonates, remains limited and the potential information recorded by δ18O and Δ47 offsets from isotopic equilibrium values is largely overlooked. Additionally, in carbonates formed in isotopic equilibrium, the use of the carbonate δ18O signature as a paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰), measured on microbial carbonates, that are strongly linked to carbonate δ18O offsets (−25 ‰) from equilibrium. These offsets are likely both related to the microorganism metabolic activity and yield identical erroneous temperature reconstructions. Unexpectedly, we show that the δ18O value of the water in which carbonates precipitated, as well as the water-carbonate δ18O fractionation dependence to temperature at equilibrium can be retrieved from these paired δ18O and Δ47 disequilibrium values measured in carbonates. The possibility to retrieve the δ18O value of paleowaters, sediments' interstitial waters or organisms' body water at the carbonate precipitation loci, even from carbonates formed in isotopic disequilibrium, opens long-awaited research avenues for both paleoenvironmental reconstructions and biomineralization studies.