The effects of diagenetic aromatization on the carbon and hydrogen isotopic composition of higher plant di- and triterpenoids: evidence from buried wood

International audienc

The use of pseudo‐MRM for a sensitive and selective detection and quantification of polycyclic aromatic compounds by tandem mass spectrometry

Rationale: Multiple Reaction Monitoring (MRM) is a sensitive and selective detection mode for target trace-level analysis. However, it requires the fragmentation of labile bonds which are not present in molecules such as Polycyclic Aromatic Hydrocarbons (PAHs) and their heterocyclic derivatives (PANHs, PASHs).Methods: We present the application of an alternative tandem mass spectrometry (MS/MS) mode called "pseudo-MRM" for the GCMS/MS analysis of Polycyclic Aromatic Compounds (PACs). This mode is based on the monitoring of transitions with no mass loss between the precursor and the product ion. Pseudo-MRM peak areas were compared with those of classic MRM on three different mass spectrometers: two triple quadrupoles and an ion trap.Results: For all non-polar PACs studied here (PAHs, PANHs and PASHs), the pseudo-MRM transition was always the most intense. The classic MRM transitions exhibited peak areas 2 to 5 times lower. On the contrary, for the functionalized PACs (oxygenated and nitrated PAHs), classic MRM was favored over pseudo-MRM. These observations were confirmed on two triple quadrupoles (QqQs), and the real-world applicability of pseudo-MRM on QqQs was validated by the successful analysis of Diesel PM. However, a comparison with an ion trap showed that pseudo-MRM was never favored on that instrument, which caused fragmentation of non-polar PACs in MS/MS.Conclusions: The results of this study show an important gain in sensitivity when using pseudo-MRM instead of MRM for non-polar PACs on QqQ instruments. The selectivity of MRM is preserved in pseudo-MRM by applying non-zero collision energies to which only these non-polar PACs are resistant, not the isobaric interferences. No interference issue was observed when analyzing Diesel PM, a complex matrix, with our pseudo-MRM method. Therefore, we advise for a broader use of this MS/MS mode for trace-level determination of non-polar PAHs

Biosynthesis of Isoprene Units in Euphorbia lathyris Laticifers vs. Other Tissues: MVA and MEP Pathways, Compartmentation and Putative Endophytic Fungi Contribution

International audienceEuphorbia species are characterized by a net of laticifers producing large amounts of triterpenes. These hydrocarbon-like metabolites can be converted into fuel by the methods of the oil industry. Euphorbia lathyris is easily grown at an industrial scale. In an attempt to increase its triterpene production, the metabolic pathways leading to isoprenoid were investigated by incorporation of 13 C labeled glucose and mevalonate and 2 H labeled deoxyxylulose as well as by natural abundance isotope ratio GC-MS. Latex triterpenes are exclusively synthesized via the mevalonate (MVA) pathway: this may orient future search for improving the triterpene production in E. lathyris. Phytosterols and their precursors are mainly derived from MVA pathway with a slight contribution of the methylerythritol phosphate (MEP) pathway, whereas phytol is issued from MEP pathway with a minor contribution of the MVA pathway: this is in accordance with the metabolic cross-talk between cytosolic and plastidial compartments in plants. In addition, hopenol B behaved differently from the other latex triterpenes. Its 13 C isotope abundance after incorporation of 13 C labeled glucose and its natural abundance δ 2 H signature clearly differed from those of the other latex triterpenes indicating another metabolic origin and suggesting that it may be synthesized by an endophytic fungus

Molecular, isotopic and radiocarbon evidence for broomcorn millet cropping in Northeast France since the Bronze Age

Molecular and isotopic investigation of lipids from soils filling several structures from an archaeological site located at Obernai (Alsace, NE France) has revealed the presence of miliacin, a triterpenoid marker from Panicum miliaceum (broomcorn millet), indicating that this cereal was cultivated at the site. The concentration profiles of miliacin within silos and its detection in other archaeological structures (e.g., Gaulish pit) suggest that miliacin did not originate from cereals stored in the silos but rather came from remains of millet from cultivated soils which filled the silos after they were abandoned. Furthermore, the 14C age of miliacin isolated from a silo of the Second Iron Age was shown to be considerably older (Bronze Age) than the structure itself, revealing that the soil filling the silo therefore archived the molecular signature from past millet cropping, predating the digging of the silo. Thus, radiocarbon dating of the isolated miliacin allowed the timing of millet cropping to be determined, showing that it was established during the Bronze Age and the Roman Gaul period at Obernai. This is the first evidence of millet cultivation in Alsace dating back to the Bronze Age, bringing new perspectives on agricultural practices and past dietary practice in Eastern France. The combination of molecular studies and radiocarbon dating of individual lipids highlights the potential of hollow structures like silos and pits to act as “pedological traps”, recording information on past vegetation cover or agricultural practices from the surface horizons of surrounding soils that filled these structures after abandonment

Les archives pédologiques : des concepts de base à la gestion des écosystèmes. Nouvelles approches en spectroscopie proche infrarouge (SPIR) et sur les biomarqueurs moléculaires lipidiques. Apports du programme GESSOL-APOGEE

Soil archives, like historical and sedimentary archives, allow past dynamics of ecosystems to be reconstructed and their current functioning to be understood. In this article, we first remind the principal specifics of soil archives, and then present two methodological approaches which were developed in the framework of the GESSOL-APOGEE program : qualitative near infrared spectroscopy and molecular plant biomarkers. These approaches are illustrated using three case studies.Au même titre que les archives historiques ou les archives sédimentaires, les archives pédologiques permettent de reconstituer la dynamique passée des écosystèmes et de mieux comprendre leur fonctionnement actuel. Après avoir rappelé les principales spécificités des archives pédologiques, nous présenterons deux approches méthodologiques développées dans le cadre du programme GESSOL-APOGEE : la spectroscopie proche infrarouge qualitative et l’analyse des biomarqueurs moléculaires végétaux. Nous illustrerons ces approches par trois exemples.Schwartz Dominique, Ertlen Damien, Froehlicher Lucie, Vyslouzilova Barbora, Bastien Claire, Courel Blandine, Schaeffer Philippe, Trendel Jean-Michel, Liaud Céline, Motsch Estelle, Adam Pierre, Šefrna Luděk, Hajdas Irka, Gierga Merle, Bernasconi Stefano. Les archives pédologiques : des concepts de base à la gestion des écosystèmes. Nouvelles approches en spectroscopie proche infrarouge (SPIR) et sur les biomarqueurs moléculaires lipidiques. Apports du programme GESSOL-APOGEE. In: Collection EDYTEM. Cahiers de géographie, numéro 18, 2015. Sols et matières organiques. Mémoires et héritages. pp. 19-32

Bacterial physiology highlighted by the δ13C fractionation of bacteriohopanetetrol isomers

Lipid biomarkers, here various bacteriohopanetetrol (BHT) isomers, are useful tools in tracing bacterially mediated nitrogen and carbon cycle processes affecting greenhouse gas emissions, such as the anaerobic oxidation of ammonia. Three isomers occur commonly in the environment. By gas chromatography, BHT-34S elutes first; it is produced by numerous bacteria. The two later eluting isomers are more constrained in their origin. The marine anammox bacteria ‘Ca. Scalindua’ is the only known producer of a BHT isomer of unknown stereochemistry (BHT-x), making BHT-x a diagnostic biomarker in anoxic marine settings. The BHT-34R isomer is produced by three freshwater aerobic heterotrophic producers (Frankia spp., Acetobacter pasteurianus, and Komagataeibacter xylinus), a freshwater serine-cycle (Type II) methanotroph (Methylocella palustris), and the freshwater anammox ‘Ca. Brocadia’, which makes the detection of freshwater anammox using BHT-34R more complicated. We investigate whether the source of BHT-34R in freshwater environments can be ascertained via its δ13C value. We used conventional on-column gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) (as opposed to high temperature GC-C-IRMS) to determine the δ13C composition of acetylated BHT isomers in cultured bacteria and bacterial enrichments. We combined these with bulk biomass and substrate δ13C compositions to establish carbon isotopic fractionation factors. The two anammox genera had large fractionation factors from dissolved inorganic carbon (DIC) to biomass (Δ13Cbiomass – DIC = –43.8 to –26.4 ‰) and to BHTs (Δ13CBHT – DIC = –53.8 to –38.2 ‰), which clearly distinguished them from the freshwater aerobic heterotrophic producers (Δ13Cbiomass – substrate = –2.3 to –0.1 ‰; Δ13CBHT – substrate = –12.8 to 5.2 ‰). Methylocella assimilated mainly carbon from DIC, rather than from methane, into its biomass and BHT, and previous work suggested this assimilation comes with relatively small fractionation. Thus, in peatlands, the BHT δ13C values of Methylocella would not reflect the low δ13C values of biogenic methane. Consequently, the presence of BHT-34R with low δ13C values relates to ‘Ca. Brocadia’ and presents a novel tool to trace anammox in freshwater environments