On the climate benefit of a coal-to-gas shift in Germany's electric power sector.

Methane emissions along the natural gas supply chain are critical for the climate benefit achievable by fuel switching from coal to natural gas in the electric power sector. For Germany, one of the world's largest primary energy consumers, with a coal and natural gas share in the power sector of 35% and 13%, respectively, we conducted fleet-conversion modelling for reference year 2018, taking domestic and export country specific greenhouse gas (GHG)-emissions in the natural gas and coal supply chains into account. Methane leakage rates below 4.9% (GWP20; immediate 4.1%) in the natural gas supply chain lead to overall reduction of CO2-equivalent GHG-emissions by fuel switching. Supply chain methane emissions vary significantly for the import countries Russia, Norway and The Netherlands, yet for Germany's combined natural gas mix lie with << 1% far below specific break-even leakage rates. Supply chain emission scenarios demonstrate that a complete shift to natural gas would emit 30-55% (GWP20 and GWP100, respectively) less CO2-equivalent GHG than from the coal mix. However, further abating methane emissions in the petroleum sector should remain a prime effort, when considering natural gas as bridge fuel on the path to achieve the Paris climate goals.

Understanding the geobiology of the terminal Ediacaran Khatyspyt Lagerstätte (Arctic Siberia, Russia).

The Khatyspyt Lagerstätte (~544 Ma, Russia) provides a valuable window into late Ediacaran Avalon-type ecosystems with rangeomorphs, arboreomorphs, and mega-algae. Here, we tackle the geobiology of this Lagerstätte by the combined analysis of paleontological features, sedimentary facies, and lipid biomarkers. The Khatyspyt Formation was deposited in carbonate ramp environments. Organic matter (0.12-2.22 wt.% TOC) displays characteristic Ediacaran biomarker features (e.g., eukaryotic steranes dominated by the C29 stigmastane). Some samples contain a putative 2-methylgammacerane that was likely sourced by ciliates and/or bacteria. 24-isopropylcholestane and 26-methylstigmastane are consistently scarce (≤0.4% and ≤0.2% of ∑C27-30 regular steranes, respectively). Thus, Avalon-type organisms occupied different niches than organisms capable of directly synthesizing C30 sterane precursors among their major lipids. Relative abundances of eukaryotic steranes and bacterial hopanes (sterane/hopane ratios = 0.07-0.30) demonstrate oligotrophic and bacterially dominated marine environments, similar to findings from other successions with Ediacara-type fossils. Ediacara-type fossils occur in facies characterized by microbial mats and biomarkers indicative for a stratified marine environment with normal-moderate salinities (moderate-high gammacerane index of 2.3-5.7; low C35 homohopane index of 0.1-0.2). Mega-algae, in contrast, are abundant in facies that almost entirely consist of allochthonous event layers. Biomarkers in these samples indicate a non-stratified marine environment and normal salinities (low gammacerane index of 0.6-0.8; low C35 homohopane index of 0.1). Vertical burrowers occur in similar facies but with biomarker evidence for stratification in the water column or around the seafloor (high gammacerane index of 5.6). Thus, the distribution of macro-organisms and burrowers was controlled by various, dynamically changing environmental factors. It appears likely that dynamic settings like the Khatyspyt Lagerstätte provided metabolic challenges for sustenance and growth which primed eukaryotic organisms to cope with changing environmental habitats, allowing for a later diversification and expansion of complex macroscopic life in the marine realm.

Recent magmatism drives hydrocarbon generation in north-east Java, Indonesia.

Conventional studies of petroleum basins associate oil generation with the gradual burial of organic-rich sediments. These classical models rely on the interplay between pressure, temperature, and the time required for organic matter transformation to oil and gas. These processes usually occur over geological timescales, but may be accelerated by rapid reactions when carbon-rich sediments are exposed to migrating magmatic fluids. The spectacular Lusi eruption (north-east Java, Indonesia) is the surface expression of the present-day deep interaction between volcanic and sedimentary domains. Here we report the ongoing generation of large amounts of hydrocarbons induced by a recent magmatic intrusion from the neighbouring Arjuno-Welirang volcanic complex. We have investigated a unique suite of oil and clast samples, and developed a detailed conceptual model for the complex hydrocarbon migration history in this part of the basin by integrating multidisciplinary techniques. Our results show that palynology, organic petrology, and chlorite microthermometry are the most sensitive geothermometers for basins affected by recent magmatic activity. These findings further our understanding of the driving mechanisms fueling the world's largest active mud eruption and provide a unique dataset to investigate modern hydrocarbon generation processes.

C35 Hopanoid Side Chain Biosynthesis: Reduction of Ribosylhopane into Bacteriohopanetetrol by a Cell-Free System Derived from Methylobacterium organophilum.

The major bacterial triterpenoids of the hopane series each consist of a C30 triterpene hopane moiety and an additional nonterpene C5 side chain derived from D-ribose and linked through its C-5 carbon atom to the hopane side chain. Bacteriohopanetetrol and aminobacteriohopanetriol are the most common representatives of this natural product series, adenosylhopane and ribosylhopane being putative precursors. Deuterium-labelled ribosylhopane was obtained by hemisynthesis and converted into deuterium-labelled bacteriohopanetetrol in the presence of NADPH, thus giving evidence of this as yet unknown precursor-to-product relationship in the bacterial hopanoid metabolic pathway.

Methanogenic capabilities of ANME-archaea deduced from (13) C-labelling approaches.

Anaerobic methanotrophic archaea (ANME) are ubiquitous in marine sediments where sulfate dependent anaerobic oxidation of methane (AOM) occurs. Despite considerable progress in the understanding of AOM, physiological details are still widely unresolved. We investigated two distinct microbial mat samples from the Black Sea that were dominated by either ANME-1 or ANME-2. The (13) C lipid stable isotope probing (SIP) method using labelled substances, namely methane, bicarbonate, acetate, and methanol, was applied, and the substrate-dependent methanogenic capabilities were tested. Our data provide strong evidence for a versatile physiology of both, ANME-1 and ANME-2. Considerable methane production rates (MPRs) from CO2 -reduction were observed, particularly from ANME-2 dominated samples and in the presence of methane, which supports the hypothesis of a co-occurrence of methanotrophy and methanogenesis in the AOM systems (AOM/MPR up to 2:1). The experiments also revealed strong methylotrophic capabilities through (13) C-assimilation from labelled methanol, which was independent of the presence of methane. Additionally, high MPRs from methanol were detected in both of the mat samples. As demonstrated by the (13) C-uptake into lipids, ANME-1 was found to thrive also under methane free conditions. Finally, C35 -isoprenoid hydrocarbons were identified as new lipid biomarkers for ANME-1, most likely functioning as a hydrogen sink during methanogenesis.

Spectral characterization of ten cyclic lipids using time-of-flight secondary ion mass spectrometry.

RATIONALE: Over the last decade, the high lateral resolution and imaging capabilities of time-of-flight secondary ion mass spectrometry (ToF-SIMS) have increasingly stimulated interest in studying organic molecules in complex environmental materials. However, unlike with the established mass spectrometric techniques, the use of ToF-SIMS in the biogeosciences is still hampered by a lack of reference spectra of the relevant biomarker compounds. Here we present and interpret ToF-SIMS reference spectra of ten different cyclic lipids that are frequently used as biological tracers in ecological, organic geochemical and geobiological studies. METHODS: Standard compounds of α,ß,ß-(20R,24S)-24-methylcholestane, (22E)-ergosta-5,7,22-trien-3ß-ol, 17α(H),21ß-(H)-30-norhopane, hope-17(21)-ene, hop-22(29)-ene, 17ß(H),21ß(H)-bacteriohopane-32,33,34,35-tetrol, 17ß(H),21ß(H)-35-aminobacteriohopane-32,33,34-triol, α-tocopherol, ß,ß-carotene, chlorophyll a, and cryosections of microbial mats and a fungus were analyzed using a ToF-SIMS instrument equipped with a Bi(3)(+) cluster ion source. RESULTS: The spectra obtained from the standard compounds showed peaks in the molecular weight range (molecular ions, protonated and deprotonated molecules, adduct ions) and diagnostic fragment ion peaks in both, positive and negative ion modes. For the cyclic hydrocarbons, however, the positive ion mode spectra typically showed more and stronger characteristic peaks than the negative ion mode spectra. Using real world samples the capability of ToF-SIMS to detect and image selected compounds in complex organic matrices was tested. 17ß(H),21ß(H)-35-Aminobacteriohopane-32,33,34-triol, carotene and chlorophyll a were successfully identified in cryosections of microbial mats, and the distribution of ergosterol was mapped at µm resolution in a cryosection of a fungus (Tuber uncinatum). CONCLUSIONS: This study further highlights the utility of ToF-SIMS for the identification and localization of lipids within environmental samples and as a technique for biomarker-related research in organic geochemistry and geobiology.

The fingerprint of chemosymbiosis: origin and preservation of isotopic biosignatures in the nonseep bivalve Loripes lacteus compared with Venerupis aurea.

Endosymbionts in marine bivalves leave characteristic biosignatures in their host organisms. Two nonseep bivalve species collected in Mediterranean lagoons, thiotrophic symbiotic Loripes lacteus and filter-feeding nonsymbiotic Venerupis aurea, were studied in detail with respect to generation and presence of such signatures in living animals, and the preservation of these signals in subfossil (late Pleistocene) sedimentary shells. Three key enzymes from sulfur oxidation (APS-reductase), CO(2) fixation (RubisCO) and assimilation of nitrogen [glutamine synthetase (GS)] were detected by immunofluorescence in the bacterial symbionts of Loripes. In Loripes, major activity was derived from GS of the symbionts whereas in Venerupis the host GS is active. In search of geologically stable biosignatures for thiotrophic chemosymbiosis that might be suitable to detect such associations in ancient bivalves, we analyzed the isotopic composition of shell lipids (δ(13)C) and the bulk organic matrix of the shell (δ(13)C , δ(15)N , δ(34)S). In the thiotrophic Loripes, δ(13)C values were depleted compared with the filter-feeding Venerupis by as much as 8.5‰ for individual fatty acids, and 4.4‰ for bulk organic carbon. Likewise, bulk δ(15)N and δ(34)S values were more depleted in recent thiotrophic Loripes. Whereas δ (34)S values were found to be unstable over time, the combined δ(15)N and δ(13)C values in organic shell extracts revealed a specific signature for chemosymbiosis in recent and subfossil specimens.

Hopanoid production by Desulfovibrio bastinii isolated from oilfield formation water.

Hopanoids are important lipid components of many bacterial groups and are therefore ubiquitous in soils, sediments, and rocks. Until recently, it was believed that the synthesis of hopanoids is restricted to at least microaerophilic bacteria and consequently geological findings of hopanoids were used as an indication for oxygenated settings. Recent studies, however, demonstrated the biosynthesis of hopanoids under strictly anoxic conditions by a few bacterial groups, although their relevance is still unclear. We therefore extended our previous work studying hopanoid production among members of the genus Desulfovibrio, a group of sulphate-reducing bacteria (SRB) widely distributed in marine sediments, water-logged soils, and oil reservoirs. We found three species (Desulfovibrio halophilus, Desulfovibrio vulgaris Hildenborough, and Desulfovibrio africanus) to be devoid of hopanoids. In contrast, Desulfovibrio bastinii contains high amounts of nonextended hopanoids and bacteriohopanepolyols, with diploptene, 17beta(H),21beta(H)-bacteriohopane-32,33,34,35-tetrol, and 17beta(H),21beta(H)-35-aminobacteriohopane-32,33,34-triol being the major compounds. Because the moderately halophilic D. bastinii was isolated from a deep subsurface oil formation water, a contribution of hopanoids by SRB to the intrinsic oil hopanoid inventory is feasible, which would influence hopanoidal compositions often used for organic-geochemical characterization purposes. Nevertheless, our data indicate that hopanoid production might be common, but not obligate in the genus Desulfovibrio.

A novel, multi-layered methanotrophic microbial mat system growing on the sediment of the Black Sea.

A novel microbially diverse type of 1- to 5-cm-thick mat performing anaerobic oxidation of methane (AOM) and covering several square metres of the seafloor was discovered in the Black Sea at 180 m water depth. Contrary to other AOM-mat systems of the Black Sea these floating mats are not associated to free gas and are not stabilized by authigenic carbonates. However, supply of methane is ensured by the horizontal orientation of the mats acting as a cover of methane enriched fluids ascending from the underlying sediments. Thorough investigation of their community composition by molecular microbiology and lipid biomarkers, metabolic activities and elemental composition showed that the mats provide a clearly structured system with extracellular polymeric substances (EPS) building the framework of the mats. The top black zone, showing high rates of AOM (15 mumol g(dw) (-1) day(-1)), was dominated by ANME-2, while the following equally active pink layer was dominated by ANME-1 Archaea. The lowest AOM activity (2 mumol g(dw) (-1) day(-1)) and cell numbers were found in the greyish middle part delimited towards the sediment by a second pink, ANME-1-dominated and sometimes a black outer layer (ANME-2). Our work clearly shows that the different microbial populations are established along defined chemical gradients such as methane, sulfate or sulfide.

Anaerobic oxidation of short-chain hydrocarbons by marine sulphate-reducing bacteria.

The short-chain hydrocarbons ethane, propane and butane are constituents of natural gas. They are usually assumed to be of thermochemical origin, but biological formation of ethane and propane has been also observed. Microbial utilization of short-chain hydrocarbons has been shown in some aerobic species but not in anaerobic species of bacteria. On the other hand, anaerobic utilization of short-chain hydrocarbons would in principle be expected because various anaerobic bacteria grow with higher homologues (> or =C(6)). Indeed, chemical analyses of hydrocarbon-rich habitats with limited or no access of oxygen indicated in situ biodegradation of short-chain hydrocarbons. Here we report the enrichment of sulphate-reducing bacteria (SRB) with such capacity from marine hydrocarbon seep areas. Propane or n-butane as the sole growth substrate led to sediment-free sulphate-reducing enrichment cultures growing at 12, 28 or 60 degrees C. With ethane, a slower enrichment with residual sediment was obtained at 12 degrees C. Isolation experiments resulted in a mesophilic pure culture (strain BuS5) that used only propane and n-butane (methane, isobutane, alcohols or carboxylic acids did not support growth). Complete hydrocarbon oxidation to CO2 and the preferential oxidation of 12C-enriched alkanes were observed with strain BuS5 and other cultures. Metabolites of propane included iso- and n-propylsuccinate, indicating a subterminal as well as an unprecedented terminal alkane activation with involvement of fumarate. According to 16S ribosomal RNA analyses, strain BuS5 affiliates with Desulfosarcina/Desulfococcus, a cluster of widespread marine SRB. An enrichment culture with propane growing at 60 degrees C was dominated by Desulfotomaculum-like SRB. Our results suggest that diverse SRB are able to thrive in seep areas and gas reservoirs on propane and butane, thus altering the gas composition and contributing to sulphide production.

Biosynthesis of hopanoids by sulfate-reducing bacteria (genus Desulfovibrio).

Sulfate reduction accounts for about a half of the remineralization of organic carbon in anoxic marine shelf regions. Moreover, it was already a major microbial process in the very early ocean at least 2.4 billion years before the present. Here we demonstrate for the first time the capability of sulfate-reducing bacteria (SRB) to biosynthesize hopanoids, compounds that are quantitatively important and widely distributed biomarkers in recent and fossil sediments dating back to the late Archean. We found high concentrations (9.8-12.3 mg per gram of dry cells) of non-extended and extended bacteriohopanoids (bacteriohopanetetrol, aminobacteriohopanetriol, aminobacteriohopanetetrol) in pure cultures of SRB belonging to the widely distributed genus Desulfovibrio. Biohopanoids were found--considered as membrane rigidifiers--in more than 50% of bacterial species analysed so far. However, their biosynthesis appeared to be restricted to aerobes or facultative anaerobes with a very few recently described exceptions. Consequently, findings of sedimentary hopanoids are often used as indication for oxygenated settings. Nevertheless, our findings shed new light on the presence of hopanoids in specific anoxic settings and suggests that SRB are substantial sources of this quantitatively important lipid class in recent but also past anoxic environments.

Subsurface microbial methanotrophic mats in the Black Sea.

A nodule-shaped microbial mat was found subsurface in sediments of a gas seep in the anoxic Black Sea. This mat was dominated by ANME-1 archaea and consumed methane and sulfate simultaneously. We propose that such subsurface mats represent the initial stage of previously investigated microbial reefs.

In vitro study of lipid biosynthesis in an anaerobically methane-oxidizing microbial mat.

The anaerobic oxidation of methane (AOM) is a key process in the global methane cycle, and the majority of methane formed in marine sediments is oxidized in this way. Here we present results of an in vitro 13CH4 labeling study (delta13CH4, approximately 5,400 per thousand) in which microorganisms that perform AOM in a microbial mat from the Black Sea were used. During 316 days of incubation, the 13C uptake into the mat biomass increased steadily, and there were remarkable differences for individual bacterial and archaeal lipid compounds. The greatest shifts were observed for bacterial fatty acids (e.g., hexadec-11-enoic acid [16:1Delta11]; difference between the delta13C at the start and the end of the experiment [Deltadelta13C(start-end)], approximately 160 per thousand). In contrast, bacterial glycerol diethers exhibited only slight changes in delta13C (Deltadelta13C(start-end), approximately 10 per thousand). Differences were also found for individual archaeal lipids. Relatively high uptake of methane-derived carbon was observed for archaeol (Deltadelta13C(start-end), approximately 25 per thousand), a monounsaturated archaeol, and biphytanes, whereas for sn-2-hydroxyarchaeol there was considerably less change in the delta13C (Deltadelta13C(start-end), approximately 2 per thousand). Moreover, an increase in the uptake of 13C for compounds with a higher number of double bonds within a suite of polyunsaturated 2,6,10,15,19-pentamethyleicosenes indicated that in methanotrophic archaea there is a biosynthetic pathway similar to that proposed for methanogenic archaea. The presence of group-specific biomarkers (for ANME-1 and ANME-2 associations) and the observation that there were differences in 13C uptake into specific lipid compounds confirmed that multiple phylogenetically distinct microorganisms participate to various extents in biomass formation linked to AOM. However, the greater 13C uptake into the lipids of the sulfate-reducing bacteria (SRB) than into the lipids of archaea supports the hypothesis that there is autotrophic growth of SRB on small methane-derived carbon compounds supplied by the methane oxidizers.

Membrane lipid patterns typify distinct anaerobic methanotrophic consortia.

The anaerobic oxidation of methane (AOM) is one of the major sinks of this substantial greenhouse gas in marine environments. Recent investigations have shown that diverse communities of anaerobic archaea and sulfate-reducing bacteria are involved in AOM. Most of the relevant archaea are assigned to two distinct phylogenetic clusters, ANME-1 and ANME-2. A suite of specific (13)C-depleted lipids demonstrating the presence of consortia mediating AOM in fossil and recent environments has been established. Here we report on substantial differences in the lipid composition of microbial consortia sampled from distinct compartments of AOM-driven carbonate reefs growing in the northwestern Black Sea. Communities in which the dominant archaea are from the ANME-1 cluster yield internally cyclized tetraether lipids typical of thermophiles. Those in which ANME-2 archaea are dominant yield sn-2-hydroxyarchaeol accompanied by crocetane and crocetenes. The bacterial lipids from these communities are also distinct even though the sulfate-reducing bacteria all belong to the Desulfosarcina/Desulfococcus group. Nonisoprenoidal glycerol diethers are predominantly associated with ANME-1-dominated communities. Communities with ANME-2 yield mainly conventional, ester-linked diglycerides. ANME-1 archaea and associated sulfate-reducing bacteria seem to be enabled to use low concentrations of methane and to grow within a broad range of temperatures. Our results offer a tool for the study of recent and especially of fossil methane environments.

The steroids of hexactinellid sponges.

The Hexactinellida ('glass sponges') are commonly considered to be the most basic metazoans. Steroids of 20 species from different taxa were studied for chemotaxonomy and biosynthetic implications. All Hexactinellida contain cholest-5-en-3beta-ol (cholesterol) and/or its saturated derivative 5alpha(H)-cholestan-3beta-ol, along with their C-24-alkylated homologues. Where 5alpha(H)-stanols are present, they regularly co-occur with their 3-keto analogues. The steroid concentrations generally decrease with increasing carbon numbers, similar to sterol distributions typically found in marine sediments. These features argue against de novo sterol biosynthesis operating in hexactinellid sponges. Rather, we suggest a dietary uptake of delta5-stenols and their stereoselective transformation via 3-keto intermediates to 5alpha(H)-stanols.

Microbial reefs in the Black Sea fueled by anaerobic oxidation of methane.

Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong 13C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea (phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcus group). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.

A chemical view of the most ancient metazoa--biomarker chemotaxonomy of hexactinellid sponges.

Hexactinellid sponges are often considered to be the most ancient metazoans. Lipid biomarkers from 23 species were studied for information on their phylogenetic properties, particularly their disputed relation to the two other sponge classes (Demospongiae, Calcarea). The most prominent lipid compounds in the Hexactinellida comprise C28 to C32 polyenoic fatty acids. Their structures parallel the unique patterns found in demosponge membrane fatty acids ('demospongic acids') and strongly support a close phylogenetic association of the Demospongiae and the Hexactinellida. Both taxa also show unusual mid-chain methylated fatty acids (C15-C25) and irregular C25- and C40-isoprenoid hydrocarbons, tracers for specific eubacteria and Archaea, respectively. These biomarkers indicate a similar, highly conservative symbiont community, although some shift in the abundance of the associated microbiota was observed. The lack of these features in calcareous sponges further contradicts the still common view that Calcarea and Demospongiae are more closely related to each other than either is to the Hexactinellida.