accounted for about 90% of total community. In the naphthalene-amended BACTRAP®, members of the SR- FBR-L83 family (Order Ignavibacteriales) accounted for almost 80% of bacterial community. Functional annotation of metagenomes showed that only the sediment sample located at the source zone border and with the lowest BTEX concentration, has metabolic potential to degrade hydrocarbons aerobically. On the other in situ hand, BACTRAP®s allowed enrichment of hydrocarbon-degrading bacteria. Metagenomic data suggest that fumarate addition is the main mechanism for hydrocarbon activation of toluene. Also, indications for methylation, hydroxylation and carboxylation as activation mechanisms for benzene anaerobic conversion were found. After 120 days of exposure in the contaminated groundwater, the isotopic analysis of fatty acids extracted from BACTRAP®s demonstrated the assimilation of isotopic labeled compounds in the cells of microbes expressed by strong isotopic enrichment. We propose that the microbiota in this jet-fuel contaminated site has metabolic potential to degrade benzene and toluene by a syntrophic process, between members of the Pelotomaculum families Geobacteraceae and Peptococcaceae (genus ), coupled to nitrate, iron and/or sulfate reduction.

Hindshaw, R.S., Tosca, R., Tosca, N.J., Tipper, E.T., 2020. Experimental constraints on Mg isotope fractionation during clay formation: Implications for the global biogeochemical cycle of Mg. Earth and Planetary Science Letters 531, 115980.

http://www.sciencedirect.com/science/article/pii/S0012821X19306727 The direction and magnitude of magnesium (Mg) isotope fractionation attendant to the formation of clay minerals is fundamental to the use of Mg isotopes to decipher the biogeochemical cycling of Mg in the critical zone and for the oceanic Mg budget. This study provides experimental data on the Mg fractionation factor for two smectite-group minerals (stevensite and saponite) at temperatures relevant for Earth surface processes. The resultant solids were characterised by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) to confirm the mineralogy and crystallinity of the product. A series of experiments were performed to asses the impact of temperature and pH on isotope fractionation. Bulk solid samples were treated with ammonium chloride to remove exchangeable Mg in order to distinguish the Mg isotopic fractionation between these sites and octahedral sites. 24 26 δ All bulk and residual solids were enriched in Mg compared to the initial solution and Mg values of the exchangeable pool were lower than, or within error of, the initial solution. Final solutions were either within 26 error of, or enriched in, Mg compared to the initial solution, depending on the fraction of Mg removed from f f solution ( Mg). For experiments with small or negligible Mg, increasing the pH resulted in a higher reaction rate and reduced fractionation from the initial solution. This could point to a kinetic effect, but the composition of the residual solid (Mg/(Li+Mg) ratio) was also dependent on pH. The change in the composition was reflected in the wavenumber of the Mg -OH stretch in FT-IR data, which is a proxy for bond strength, and 3 suggests an equilibrium control. An equilibrium control is further supported by the observation of reduced fractionation compared to the initial solution with increasing temperature. Rayleigh and batch fractionation models were fitted to the data giving fractionation factors of 0.9991 and 0.9990 respectively. We compare our results with existing field and experimental data and suggest that the apparent contradictions surrounding the direction of Mg isotope fractionation into phyllosilicate minerals could be due to the similarity of Mg bond lengths between clay octahedral sites and dissolved Mg. Thus small changes in mineral structure or initial solution conditions may result in a change in bond length sufficient to alter the direction of fractionation, implying that the magnitude and direction of Mg isotope fractionation into clay minerals could be dependent on local field conditions. Alternatively, if the precipitation of secondary clay minerals in the field preferentially incorporates light Mg, as observed in this experimental study, this implies the contribution of carbonate weathering to dissolved Mg fluxes has been underestimated, with major implications for the global biogeochemical cycle of Mg.

Hoffmann, R., Bestwick, J., Berndt, G., Berndt, R., Fuchs, D., Klug, C., 2020. Pterosaurs ate soft-bodied cephalopods (Coleoidea). Scientific Reports 10, 1230.

https://doi.org/10.1038/s41598-020-57731-2