Aromatic hydrocarbons provide new insight into carbonate concretion formation and the impact of eogenesis on organic matter

Investigations of aromatic biomarkers extracted from carbonate concretions can contribute to characterization of the enhanced microbial activity that mediates carbonate concretion formation. This microbial footprint can be further inferred from the stable isotopic values of carbonate (δ13C) and pyrite (δ34S). Here, we used a combination of GC–MS and GC × GC-ToF-MS to compare the aromatic fractions of two Toarcian carbonate concretions from the H. falciferum ammonite zone of the Posidonia Shale (SW-Germany) and their host sediment. The results revealed that n-alkylated and phytanyl arenes were enhanced in the concretions, relative to the host sediment. These findings support a very early diagenetic (eogenetic) microbial source for alkylated and phytanyl arenes derived from the microbial ecosystem mediating concretion formation. In contrast, aromatic compounds formed by thermal maturation (e.g. polycyclic aromatic hydrocarbons, aromatic steroids, organic sulphur compounds) remained invariant in host rock and concretion samples. When combined with bulk sediment and concretion properties, the distribution of aromatic compounds indicates that eogenetic microbial activity upon concretion growth does not diminish organic matter quality

Direct Binding of a Hepatitis C Virus Inhibitor to the Viral Capsid Protein

Over 130 million people are infected chronically with hepatitis C virus (HCV), which, together with HBV, is the leading cause of liver disease. Novel small molecule inhibitors of Hepatitis C virus (HCV) are needed to complement or replace current treatments based on pegylated interferon and ribavirin, which are only partially successful and plagued with side-effects. Assembly of the virion is initiated by the oligomerization of core, the capsid protein, followed by the interaction with NS5A and other HCV proteins. By screening for inhibitors of core dimerization, we previously discovered peptides and drug-like compounds that disrupt interactions between core and other HCV proteins, NS3 and NS5A, and block HCV production. Here we report that a biotinylated derivative of SL209, a prototype small molecule inhibitor of core dimerization (IC50 of 2.80 µM) that inhibits HCV production with an EC50 of 3.20 µM, is capable of penetrating HCV-infected cells and tracking with core. Interaction between the inhibitors, core and other viral proteins was demonstrated by SL209–mediated affinity-isolation of HCV proteins from lysates of infected cells, or of the corresponding recombinant HCV proteins. SL209-like inhibitors of HCV core may form the basis of novel treatments of Hepatitis C in combination with other target-specific HCV drugs such as inhibitors of the NS3 protease, the NS5B polymerase, or the NS5A regulatory protein. More generally, our work supports the hypothesis that inhibitors of viral capsid formation might constitute a new class of potent antiviral agents, as was recently also shown for HIV capsid inhibitors

Cryosphere carbon dynamics control early Toarcian global warming and sea level evolution

© 2018 The Earth's cryosphere represents a huge climate-sensitive carbon reservoir capable of releasing carbon dioxide (CO2) and methane (CH4) from permafrost soils or gas reservoirs capped by permafrost and ice caps upon rising global temperatures. Carbon release from these reservoirs has the potential to further accelerate global warming. Present day cryosphere demise is a focus of scientific research. The potential role of cryosphere carbon reservoirs in Mesozoic climate perturbations is even lesser known and currently underinvestigated. In contrast to previous views of a constantly warm Early Jurassic period, virtually lacking a cryosphere, recent studies have identified icehouse conditions for this time interval. Following these icehouse conditions, global warming occurred during the early Toarcian (~183 Ma) and was accompanied by a major carbon cycle anomaly as manifested in recurring negative carbon isotope excursions (CIEs). We propose that an initially volcanic-driven gentle rise of atmospheric temperature in the Early Toarcian triggered a melt-down of Earth's cryosphere which during the preceding Pliensbachian had expanded to the mid-latitudes and thus was highly vulnerable to warming. The rapid release of greenhouse gases, mainly as 13C-depleted CH4, or its oxidation product CO2, is recorded in the carbon isotope ratios of sedimentary organic matter and carbonates. Toarcian sediments display a series of orbitally-forced negative CIEs characterized by a frequency shift from eccentricity to obliquity cycles comparable to Pleistocene climate rhythms. This pattern is explained by a self-sustaining destabilization of labile cryosphere carbon reservoirs which started at mid-latitudes where eccentricity is most effective and then rhythmically progressed poleward to latitudes where obliquity dominates. The hitherto underestimated presence of a temperature-sensitive Pliensbachian cryosphere constituted an essential precondition for the early Toarcian climate change and its associated sea-level rise. The Pliensbachian cooling had transferred water into the terrestrial cryosphere causing a severe sea-level fall. Transgressive pulses at the Pliensbachian-Toarcian boundary and in the early Toarcian occurred concomitant to rising global temperatures and resulted from the meltdown of continental ice caps. This ice-volume effect and the massive discharge of freshwater into the oceans is well preserved in the exceptionally low d18O values of carbonates formed during the cryosphere demise and sea-level increase. Carbon and oxygen isotope ratios, climate and sea-level shifts thus underpin the presence of an Early Jurassic cryosphere and thereby highlight the role of glacio-eustatic mechanisms as main drivers of late Pliensbachian to early Toarcian geodynamics

Environmental response to the early Toarcian carbon cycle and climate perturbations in the northeastern part of the West Tethys shelf

Early Toarcian (Early Jurassic; ~183 Ma) climate and carbon cycle perturbations were accompanied by widespread accumulation of bituminous sediments, formed during the Toarcian Oceanic Anoxic Event (T-OAE). On the northwestern Tethyan shelf, organic carbon accumulation was particularly widespread in hydrodynamically restricted regions of the European Epicontinental Basin System (EEBS) where it peaked during the formation of euxinic waters extending into the photic zone. In the adjacent northeastern West Tethys shelf (NE-WTS), an area proximal to the deeper and better ventilated NW Tethys, deposition of strata enriched in organic matter was restricted to depressions of limited spatial extent. While numerous works have addressed the bituminous strata from the EEBS, evolution of environmental conditions and drivers of organic matter accumulation in areas proximal to the open Tethys have received much less attention. Here, we investigated a stratigraphically well-constrained, exceptionally organic matter-rich sediment succession from the NE- WTS deposited during the T-OAE. Organic and isotope geochemical investigations provided insights into the evolution and dynamics of environmental conditions during the T-OAE in a setting proximal to the Tethys. The sedimentary rocks sampled for this study originated from a surface outcrop that experienced weathering-related alteration of its mineral constituents. In particular, sulfides (mainly pyrite) were significantly altered, resulting in a near-quantitative loss of sulfur. In contrast, kerogen as well as bitumen fractions have not been significantly affected by weathering processes and carry a robust paleoenvironmental signal. The new data show that organic carbon accumulation occurred as a direct response to changing environmental conditions that also led to the early Toarcian carbon cycle perturbation. Increase in organic carbon burial occurred in a stepwise manner, following multiple injections of 12 C-enriched carbon into the Earth's ocean-atmosphere system. High algal productivity and the subsequent organic matter decomposition by sulfate reducing bacteria led to an expansion of H 2 S-rich waters into the photic zone, which promoted the growth of Chlorobiaceae. A steady increase in nitrogen isotope values testified to intensified denitrification in an expanded oxygen minimum zone. The resulting decline in the availability of bio-utilizable nitrogen in combination with harsh environmental conditions promoted the proliferation of cyanobacteria as indicated by increasing abundances of 2a-methyl-hopanes. Formation of euxinic waters in the NE-WTS was not associated with a freshwater driven salinity stratification. Organic geochemical salinity indicators (methylated chromanes) attest to normal marine salinity, supporting a strong influence of Tethyan water masses. This study enhances our knowledge on the environmental response towards the early Toarcian climate and carbon cycle perturbations in a setting proximal to the Tethys. We demonstrate that photic zone euxinia was a common and particularly widespread feature of the T-OAE and has not been confined to the hydrodynamically restricted EEBS

Eccentricity paced paleoenvironment evolution and microbial community structure in the Gulf of Mexico during the outgoing Early Eocene Climate Optimum

Orbital-driven climate fluctuations and associated variations in the carbon cycle over short- and long-term time scales can be recorded in sedimentary archives. Bulk geochemical, biomarker, and stable isotope signatures in sediments deposited at the end of the Early Eocene Climatic Optimum (EECO) recovered from the Chicxulub impact crater in the Gulf of Mexico show a strong relationship with Milankovitch cycles, which play a critical role in controlling climatic and environmental oscillations. Our study represents the first highly spatially-resolved biomarker and bulk geochemical record from the EECO. The bulk δ13Ckerogen data records the Milankovitch eccentricity-paced variability of continental weathering throughout the studied interval. Biomarkers (and indices) indicative of redox conditions [e.g., pristane (Pr)/phytane (Ph) ratios], water column stratification and/or salinity conditions (e.g., Gammacerane Index), photic zone euxinia (e.g., isorenieratane, chlorobactene, and okenane) and those that can differentiate between algal communities such as dinoflagellates (dinosteranes), marine pelagophytes (24-n-propylcholestane), chlorophyte algae (24-iso-propylcholestane), and prasinophytes (C28/C29 sterane ratios) show changes controlled by orbital eccentricity frequencies. In particular, eccentricity maxima were marked by more reducing/salinity stratified water conditions, photic zone euxinic episodes, and higher (relative) abundances of prasinophytes. In contrast, eccentricity minima were marked by more oxic water conditions and an increase in cyanobacterial markers. The δ13C offset observed between phytane and C17–C19 n-alkanes may represent shifts between a predominance of autotrophic vs. heterotrophic communities controlled by orbital eccentricity. The direct response of molecular and isotopic composition of organic matter to orbitally controlled climate change in the early Eocene could be proven here for the first time and may be more prevalent in Paleogene sediments worldwide