Metatranscriptomics reveal differences in in situ energy and nitrogen metabolism among hydrothermal vent snail symbionts

Despite the ubiquity of chemoautotrophic symbioses at hydrothermal vents, our understanding of the influence of environmental chemistry on symbiont metabolism is limited. Transcriptomic analyses are useful for linking physiological poise to environmental conditions, but recovering samples from the deep sea is challenging, as the long recovery times can change expression profiles before preservation. Here, we present a novel, in situ RNA sampling and preservation device, which we used to compare the symbiont metatranscriptomes associated with Alviniconcha, a genus of vent snail, in which specific host–symbiont combinations are predictably distributed across a regional geochemical gradient. Metatranscriptomes of these symbionts reveal key differences in energy and nitrogen metabolism relating to both environmental chemistry (that is, the relative expression of genes) and symbiont phylogeny (that is, the specific pathways employed). Unexpectedly, dramatic differences in expression of transposases and flagellar genes suggest that different symbiont types may also have distinct life histories. These data further our understanding of these symbionts' metabolic capabilities and their expression in situ, and suggest an important role for symbionts in mediating their hosts' interaction with regional-scale differences in geochemistry

Jena Reference Air Set (JRAS): a multi-point scale anchor for isotope measurements of CO₂ in air

The need for a unifying scale anchor for isotopes of CO2 in air was brought to light at the 11th WMO/IAEA Meeting of Experts on Carbon Dioxide in Tokyo 2001. During discussions about persistent discrepancies in isotope measurements between the worlds leading laboratories, it was concluded that a unifying scale anchor for Vienna Pee Dee Belemnite (VPDB) of CO2 in air was desperately needed. Ten years later, at the 2011 Meeting of Experts on Carbon Dioxide in Wellington, it was recommended that the Jena Reference Air Set (JRAS) become the official scale anchor for isotope measurements of CO2 in air (Brailsford, 2012). The source of CO2 used for JRAS is two calcites. After releasing CO2 by reaction with phosphoric acid, the gases are mixed into CO2-free air. This procedure ensures both isotopic stability and longevity of the CO2. That the reference CO2 is generated from calcites and supplied as an air mixture is unique to JRAS. This is made to ensure that any measurement bias arising from the extraction procedure is eliminated. As every laboratory has its own procedure for extracting the CO2, this is of paramount importance if the local scales are to be unified with a common anchor. For a period of four years, JRAS has been evaluated through the IMECC1 program, which made it possible to distribute sets of JRAS gases to 13 laboratories worldwide. A summary of data from the six laboratories that have reported the full set of results is given here along with a description of the production and maintenance of the JRAS scale anchors

δ¹⁸O anchoring to VPDB: calcite digestion with ¹⁸O-adjusted ortho-phosphoric acid

Abstract For anchoring CO2 isotopic measurements on the δ18OVPD-CO2 scale, the primary reference material (NBS 19 calcite) needs to be digested using concentrated ortho-phosphoric acid. During this procedure, great care must be taken to ensure that the isotopic composition of the liberated gas is accurate. Apart from controlling the reaction temperature to ±0.1°C, the potential for oxygen isotope exchange between the produced CO2 and water must be kept to a minimum. The water is usually assumed to reside on the walls in the headspace of the reaction vessel. We demonstrate here that a large fraction of the exchange may also occur with water inside the acid. Our results indicate that both exchange reactions have a significant impact on the results and may have largely been responsible for scale inconsistencies between laboratories in the past. The extent of CO2/H2O oxygen exchange depends on the concentration (amount of free water) in the acid. For acids with a nominal H3PO4 mass fraction of less than 102%, oxygen isotope exchange can create a substantial isotopic bias during high-precision measurements with the degree of the alteration being proportional to the effective isotopic contrast between the acid and the CO2 released from the calcite. Water evaporating from the acid at 25°C has a δ18O value of −34.5‰ relative to the isotopic composition of the whole acid. This large fractionation is likely to occur in two steps; by exchange with phosphate, water inside the acid is decreased in oxygen-18 relative to the bulk acid by ∼ −22‰. This water is then fractionated further during evaporation. Oxygen exchange with both water inside the acid and water condensate in the headspace can contribute to the measured isotopic signature depending on the experimental parameters. The system employed for this study has been specifically designed to minimize oxygen exchange with water. However, the amount of altered CO2 for a 95% H3PO4 at 25°C still accounts for about 3% of the total CO2 produced from a 40 mg calcite sample, resulting in a δ18O range of about 0.8‰ when varying the δ18O value of the acid by 25‰. Least biased results for NBS19-CO2 were obtained for an acid with a δ18O value close to +23‰ vs. VSMOW. In contrast, commercial acids from several sources had an average δ18O value of +13‰, amounting to a 10‰ offset from the optimal value. This observation suggests that the well-known scale incompatibilities between laboratories could arise from this difference with measurements that may have suffered systematically from non-optimal acid-δ18O values, thus producing variable offsets, depending on the experimental details. As a remedy, we suggest that the δ18O of phosphoric acid reacted with calcites for establishing a δ18O scale anchor be adjusted, and this should reduce the variability of the δ18O of CO2 evolved in acid digestion to less than ±0.05‰. The adjustment should be made by taking into account the difference in δ18O between the calcite-CO2 and the acid, with a target difference of 16‰. With this strategy, agreement between δ18O scales based on water, atmospheric CO2, and carbonates as well as data compatibility between laboratories may be substantially improved. Copyright © 2011 John Wiley & Sons, Ltd

Automated simultaneous measurement of the δ¹³C and δ²H values of methane and the δ¹³C and δ¹⁸O values of carbon dioxide in flask air samples using a new multi cryo-trap/gas chromatography/isotope ratio mass spectrometry system

RATIONALE: The isotopic composition of greenhouse gases helps to constrain global budgets and to study sink and source processes. We present a new system for high-precision stable isotope measurements of carbon, hydrogen and oxygen in atmospheric methane and carbon dioxide. The design is intended for analyzing flask air samples from existing sampling programs without the need for extra sample air for methane analysis. METHODS: CO2 and CH4 isotopes are measured simultaneously using two isotope ratio mass spectrometers, one for the analysis of δ13Candδ18Ovalues and the second one for δ2Hvalues. The inlet carousel delivers air from 16 sample positions (glass flasks 1-5 L and high-pressure cylinders). Three 10-port valves take aliquots fromthe sample stream.CH4 from100-mL air aliquots is preconcentrated in 0.8-mL sample loops using a new cryo-trap system. A precisely calibrated working reference air is used in parallel with the sample according to the Principle of Identical Treatment. RESULTS: It takes about 36 hours for a fully calibrated analysis of a complete carousel including extractions of four working reference and one quality control reference air. Long-term precision values, as obtained from the quality control reference gas since 2012, account for 0.04‰(δ13C values of CO2), 0.07‰(δ18Ovalues of CO2), 0.11‰(δ13C values ofCH4) and 1.0‰(δ2H values of CH4). Within a single day, the system exhibits a typical methane δ13C standard deviation (1σ) of 0.06‰for 10 repeated measurements. CONCLUSIONS: The system has been in routine operation at the MPI-BGC since 2012. Consistency of the data and compatibility with results from other laboratories at a high precision level are of utmost importance. A high sample throughput and reliability of operation are important achievements of the presented systemto cope with the large number of air samples to be analyzed