For the measurement of compound-specific isotope ratios by liquid chromatography isotope ratio mass spectrometry (LC-IRMS), complete mineralization of organic compounds to a single species of measurement gas is required so that isotopic fractionation can be minimized and corrected by identical treatment with standards. The established use of peroxydisulfate in an acidic environment has its limitations, especially when it comes to the complete oxidation of nitrogen-containing compounds with aromatic ring systems. Under acidic oxidation conditions, ammonium and nitrate were identified as the main nitrogen containing mineralization products of the oxidation of different model compounds. In contrast to the oxidation in an acidic environment, alkaline peroxydisulfate oxidation leads to nitrate as a final mineralization product. The concept of alkaline oxidation was transferred from large-scale batch experiments to a commercially available oxidation reactor used in LC-IRMS systems. The obtained nitrate recoveries indicate that alkaline oxidation could be a promising step towards the measurement of compound-specific nitrogen isotope ratios by LC-IMRS. In our work, we show that alkaline peroxydisulfate oxidation allows faster and more complete mineralization of nitrogen-containing compounds. For several model compounds, 63 to 100

Rationale: The analysis of nitrogen isotopes in aqueous dissolved nitrate is an effective method for identifying pollution sources and offers the potential to study the nitrogen cycle. However, the measurement of nitrogen isotope ratios of nitrate still requires extensive sample preparation or derivatization. Methods: In this study, a modified commercially available liquid chromatography-isotope ratio mass spectrometer (LC-IRMS) interface is presented that enables automated measurement of delta N-15 signatures from nitrate by online reduction of nitrate in two consecutive steps. First, vanadium(III) chloride is used as a reducing agent to convert NO3- to NxOy under acidic conditions. The mix of nitrogen oxides is then transferred into a stream of helium and reduced to nitrogen (N-2) analysis gas via a hot copper reactor. Prior to the online conversion of aqueous nitrate into elemental nitrogen, the sample was chromatographically separated from potential matrix effects on a PGC column. Results: Precision was achieved at a level below 1.4 parts per thousand by injecting 10 mu L of 50 mg L-1 N, using five different nitrate standards and reference materials. These materials spanned a range of more than 180 parts per thousand in delta N-15. To demonstrate the applicability of the method, we measured water samples from an enrichment experiment, where isotopically enriched ammonium chloride was administered into a small river over the course of 2 weeks. In contrary to our expectation, the delta N-15 values of river nitrate showed values between +0.4 +/- 0.4 parts per thousand and +4.1 +/- 0.3 parts per thousand, varying over a small range of 3.7 parts per thousand. Conclusions: Our study showed that the measurement of nitrate nitrogen isotope ratios with a modified LC-IRMS system is possible but that further modifications and improvements would be necessary for a robust and user-friendly instrument.

Flächendesinfektionen sind im Gesundheitsdienst und inzwischen auch in vielen anderen Branchen alltägliche Routine. Die eingesetzten Desinfektionsmittel enthalten teilweise Stoffe, die in die Luft gelangen und zu einer Exposition der Beschäftigten führen können. In einer Prüfkabine wurden Flächendesinfektionsarbeiten unter realistischen Bedingungen nachgestellt und die inhalative Exposition gegenüber diesen Stoffen bestimmt. Als Desinfektionsmittel wurden handelsübliche Produkte für die Wischdesinfektion ausgewählt. Die Produkte enthielten die Wirkstoffe Ethanol, Glutaraldehyd, eine Mischung aus Glutaraldehyd und Formaldehyd sowie eine Mischung aus Peroxyessigsäure und Wasserstoffperoxid. Die Messungen haben gezeigt, wie sich die Wirkstoffe auf eine Exposition auswirken können und bis zu welchen Flächengrößen sicheres Arbeiten möglich ist. Zudem ergab sich durch die gute Reproduzierbarkeit der Daten die Möglichkeit, Berechnungsmodelle zu überprüfen.

Earth's mantle releases 38.7 ± 2.9 Tg/yr CO2 along with other reduced and oxidized gases to the atmosphere shaping microbial metabolism at volcanic sites across the globe, yet little is known about its impact on microbial life under non-thermal conditions. Here, we perform comparative metagenomics coupled to geochemical measurements of deep subsurface fluids from a cold-water geyser driven by mantle degassing. Key organisms belonging to uncultivated Candidatus Altiarchaeum show a global biogeographic pattern and site-specific adaptations shaped by gene loss and inter-kingdom horizontal gene transfer. Comparison of the geyser community to 16 other publicly available deep subsurface sites demonstrate a conservation of chemolithoautotrophic metabolism across sites. In silico replication measures suggest a linear relationship of bacterial replication with ecosystems depth with the exception of impacted sites, which show near surface characteristics. Our results suggest that subsurface ecosystems affected by geological degassing are hotspots for microbial life in the deep biosphere.

Microorganisms are present in nearly every oil or bitumen sample originating from temperate reservoirs. Nevertheless, it is very difficult to obtain reliable estimates about microbial processes taking place in deep reservoirs, since metabolic rates are rather low and differ strongly during artificially cultivation. Here, we demonstrate the importance and impact of microorganisms entrapped in microscale water droplets for the overall biodegradation process in bitumen. To this end, we measured degradation rates of heavily biodegraded bitumen from the Pitch Lake (Trinidad and Tobago) using the novel technique of reverse stable isotope labeling, allowing precise measurements of comparatively low mineralization rates in the ng range in microcosms under close to natural conditions. Freshly taken bitumen samples were overlain with artificial brackish water and incubated for 945 days. Additionally, three-dimensional distribution of water droplets in bitumen was studied with computed tomography, revealing a water bitumen interface of 1134 cm2 per liter bitumen, resulting in an average mineralization rate of 9.4–38.6 mmol CO2 per liter bitumen and year. Furthermore, a stable and biofilm-forming microbial community established on the bitumen itself, mainly composed of fermenting and sulfate-reducing bacteria. Our results suggest that small water inclusions inside the bitumen substantially increase the bitumen–water interface and might have a major impact on the overall oil degradation process.

Intraspecific diet specialization, usually driven by resource availability, competition and predation, is common in natural populations. However, the role of parasites on diet specialization of their hosts has rarely been studied. Eye flukes can impair vision ability of their hosts and have been associated with alterations of fish feeding behavior. Here it was assessed whether European perch ( Perca fluviatilis ) alter their diet composition as a consequence of infection with eye flukes. Young-of-the-year (YOY) perch from temperate Lake Müggelsee (Berlin, Germany) were sampled in two years, eye flukes counted and fish diet was evaluated using both stomach content and stable isotope analyses. Perch diet was dominated by zooplankton and benthic macroinvertebrates. Both methods indicated that with increasing eye fluke infection intensity fish had a more selective diet, feeding mainly on the benthic macroinvertebrate Dikerogammarus villosus , while less intensively infected fish appeared to be generalist feeders showing no preference for any particular prey type. Our results show that infection with eye flukes can indirectly affect interaction of the host with lower trophic levels by altering the diet composition and highlight the underestimated role of parasites in food web studies.

Mantle degassing provides a substantial amount of reduced and oxidized gases shaping microbial metabolism at volcanic sites across the globe, yet little is known about its impact on microbial life under non-thermal conditions. Here, we characterized deep subsurface fluids from a cold-water geyser driven by mantle degassing using genome-resolved metagenomics to investigate how the gases impact the metabolism and activity of indigenous microbes compared to non-impacted sites. While species-specific analyses of Altiarchaeota suggest site-specific adaptations and a particular biogeographic pattern, chemolithoautotrophic core features of the communities appeared to be conserved across 17 groundwater ecosystems between 5 and 3200 m depth. We identified a significant negative correlation between ecosystem depth and bacterial replication, except for samples impacted by high amounts of subsurface gases, which exhibited near-surface activity. Our results suggest that geological degassing leads to higher nutrient flows and microbial activity in the deep subsurface than previously estimated.

Parasitism is commonly recognised as a consumer strategy, although, the interaction of parasites in communities and ecosystems are generally poorly understood. As parasites are integral parts of food webs, analysis of the trophic interactions between parasites and hosts was assessed through comparison of stable isotope ratios of carbon ( 13 C/ 12 C) and nitrogen ( 15 N/ 14 N). Largemouth yellowfish ( Labeobarbus kimberleyensis ) infected with the Asian tapeworm ( Schyzocotyle acheilognathi ) were collected from the Vaal Dam. Signatures of δ 13 C and δ 15 N were assessed in host muscle and liver tissue, and cestodes using an elemental analyser coupled with an isotope ratio-mass spectrometer (EA-IRMS). Hosts were enriched by 4.1‰ in the heavy nitrogen isotope with respect to the S. acheilognathi and therefore occupy a higher trophic position than the parasite. Comparison of δ 13 C indicates that dietary sources of carbon in cestodes are derived from the host liver. Comparison of stable isotope signatures between Paradiplozoon ichthyoxanthon (another common parasite of the Largemouth yellowfish in the Vaal River) and S. acheilognathi showed that the monogenean was enriched by 5.3‰ in 15 N which accounts for a difference of almost two trophic positions. Isotope differences in the host–parasite system considered indicate that differences can be related to the mode of nutrient acquisition employed by host and parasites. Cestodes, being depleted in both 13 C and 15 N relative to the host and monogenean ( P. ichthyoxanthon ), indicate that S. acheilognathi assimilates nutrients derived from the host metabolism which are released from the liver.

Stable isotope analysis offers a unique tool for comparing trophic interactions and food web architecture in ecosystems based on analysis of stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) in organisms. Clarias gariepinus were collected from six sites along the Vaal River, South Africa and were assessed for ectoparasites and endoparasites. Lamproglena clariae (Copepoda), Tetracampos ciliotheca and Proteocephalus glanduligerus (Cestoda), and larval Contracaecum sp. (Nematoda) were collected from the gills, intestine and mesenteries, respectively. Signatures of δ13C and δ15N were analysed in host muscle tissue and parasites using bulk stable isotope analysis. Variable stable isotope enrichment between parasites and host were observed; L. clariae and the host shared similar δ15N signatures and endoparasites being depleted in δ13C and δ15N relative to the host. Differences in stable isotope enrichment between parasites could be related to the feeding strategy of each parasite species collected. Geographic and spatial differences in enrichment of stable isotopes observed in hosts were mirrored by parasites. As parasites rely on a single host for meeting their nutritional demands, stable isotope variability in parasites relates to the dietary differences of host organisms and therefore variations in baseline stable isotope signatures of food items consumed by hosts.

In liquid chromatography coupled to isotope ratio mass spectrometry (LC-IRMS), analytes are separated on an LC system and consecutively oxidized to CO2, which is required for the determination of compound-specific carbon isotope ratios. Oxidation is performed in an online reactor by sulfate radicals. Reaction conditions in the interface depend on the flow conditions determined by the LC method and the flow rates and concentrations of oxidation agent and phosphoric acid added in the interface. To determine accurate isotope ratios, a quantitative conversion of the carbon contained in the analyte to the CO2 measurement gas is a prerequisite. Oxidation efficiencies are not commonly evaluated during method development, although certain analytes are known to be difficult to be oxidized by sulfate radicals. For the assessment of the oxidation efficiency of the LC-IRMS system, three different approaches were evaluated. (1) Residual organic carbon in the eluent stream of the interface was determined to calculate oxidation yields depending on the initial analyte concentration. (2) The IRMS response was calibrated to an inorganic carbon reference material to determine oxidation efficiencies with the help of the IRMS as a detector. (3) The oxidation temperature was deliberately reduced while monitoring the δ13C and signal intensity. The common assumption that a linear relation of IRMS signal to analyte concentration is an indicator for complete oxidation in LC-IRMS could be disproved. All three approaches can be applied for future method development in LC-IRMS, monitoring of existing flow injection applications, as well as for verification of complete oxidation in established LC-IRMS methods.

Peroxydisulfate (S2O82-) is widely applied in environmental remediation and water treatment as an agent for the unselective oxidation of organic contaminants. S2O82- itself is a strong oxidation agent but activation by heat, UV radiation, or metal catalysts forms sulfate radicals (SO4 center dot-), which offer a higher oxidation potential and faster reaction kinetics. The mechanism of degradation for many organic contaminants by sulfate radicals is well studied, but the final mineralization products are not commonly evaluated. Nitrogen containing compounds are known to produce different mineralization products depending on their structure and the reaction conditions. For the identification of the main mineralization products, two approaches for the determination of nitrogen mass balances were evaluated. The first approach was based on a combination of total organic carbon (TOC), and total nitrogen bound (TNb). The second approach used a combination of TOC and ion chromatography (IC). The evaluation based on the TOC and TNb by high temperature combustion was found to be significantly biased as measured ammonium concentrations were underestimated by the TNb measurements in the presence of peroxydisulfate. With the TOC/TNb method, 83.2 +/- 1.1% of the initial nitrogen could be recovered after the oxidation. The TOC/IC based approach led to an overall recovery of 91.1 +/- 1.4%, where NO3- and NH4+ were identified as the main products. Based on the fraction of ammonium provided by the IC measurements, the TOC/TNb based results could be corrected for the underestimation of ammonium which led to a recovery of 95.9 +/- 3.1%. The presented methods are applicable for the determination of nitrogen mass balances in lab-scale studies, as well as for the monitoring of mineralization products in field applications.

The sugar replacement compound xylitol has gained increasing attention because of its use in many commercial food products, dental-hygiene articles, and pharmaceuticals. It can be classified by the origin of the raw material used for its production. The traditional "birch xylitol" is considered a premium product, in contrast to xylitol produced from agriculture byproducts such as corn husks or sugar-cane straw. Bulk stable-isotope analysis (BSIA) and compound-specific stable-isotope analysis (CSIA) by liquid-chromatography isotope-ratio mass spectrometry (LC-IRMS) of chewing-gum extracts were used to determine the δ13C isotope signatures for xylitol. These were applied to elucidate the original plant type the xylitol was produced from on the basis of differences in isotope-fractionation processes of photosynthetic CO2 fixation. For the LC-IRMS analysis, an organic-solvent-free extraction protocol and HPLC method for the separation of xylitol from different artificial sweeteners and sugar-replacement compounds was successfully developed and applied to the analysis of 21 samples of chewing gum, from which 18 could be clearly related to the raw-material plant class.

BACKGROUND:Bacterial growth as a function of nutrients has been studied for decades, but is still not fully understood. In particular, the growth laws under dynamically changing environments have been difficult to explore, because of the rapidly changing conditions. Here, we address this challenge by means of a robotic assay and measure bacterial growth rate, promoter activity and substrate level at high temporal resolution across the entire growth curve in batch culture. As a model system, we study E. coli growing under nitrogen or carbon limitation, and explore the dynamics in the last generation of growth where nutrient levels can drop rapidly. RESULTS:We find that growth stops abruptly under limiting nitrogen or carbon, but slows gradually when nutrients are not limiting. By measuring growth rate at a 3 min time resolution, and inferring the instantaneous substrate level, s, we find that the reduction in growth rate μ under nutrient limitation follows Monod's law, μ=μ0(s/(k(s)+s)). By following promoter activity of different genes we found that the abrupt stop of growth under nitrogen or carbon limitation is accompanied by a pulse-like up-regulation of the expression of genes in the relevant nutrient assimilation pathways. We further find that sharp stop of growth is conditional on the presence of regulatory proteins in the assimilation pathway. CONCLUSIONS:The observed sharp stop of growth accompanied by a pulsed expression of assimilation genes allows bacteria to compensate for the drop in nutrients, suggesting a strategy used by the cells to prolong exponential growth under limiting substrate.