Search Results (462)

Methanogens, or methanogenic archaea (MA), are among the most ancient and widely distributed microorganisms, characterized by a unique metabolism that generates methane (CH₄) as the terminal product of anaerobic respiration. Their ability to grow and/or survive across a wide range of environmental conditions has made methanogens key contributors to biogeochemical cycles throughout most of Earth’s history. Most importantly, these oxygen-sensitive microorganisms have regulated the climate since the early Archean and impacted biogeochemical cycles throughout Earth’s history by producing the potent greenhouse gas, CH₄, while consuming H₂, CO₂, and small organic molecules. Hence, methanogens are attributed a key role in the start and end of several Proterozoic glaciations and mass extinction events. Their specific roles in the long-term carbon cycle that focus on CH₄ production are well-established, but, in contrast, only very few studies report on interactions with CaCO₃ and long-term carbon storage. Methanogens evolved early during Earth’s history, likely during the Archaean Eon, in layered benthic microbial communities called microbial mats. When lithified, these mats form microbialites that represent some of the earliest evidence of life in the fossil record, dating back >3.5 Gy. Methanogens are an integral part of contemporary microbial mats and have been identified both in the anoxic and oxic zones of these sedimentary ecosystems; however, their adaptations to apparently unfavorable oxic conditions and their role in the precipitation of carbonate in mats are unclear. In addition to an important role in the evolution of our planet by producing CH₄, methanogens may also produce a biosignature that could be relevant for astrobiology research. This review will discuss the diversity, physiology, and ecology of methanogens in detail to clarify their role in some of the major biogeochemical processes and ecological climatic events through the fluctuating environmental conditions on Earth through geologic time. Full article

This review examines the role of sulfate-reducing bacteria in the anaerobic degradation of hydrocarbons in marine sediments, where they contribute to the mineralization of organic matter under anoxic conditions. The metabolic diversity of these microorganisms is described, including their ability to degrade various classes of hydrocarbons such as short-chain (C₂–C₅), medium-chain (C₆–C₁₂), and long-chain (C₁₃–C₂₀₊) alkanes, alkenes, and aromatic compounds like naphthalene and phenanthrene. The primary mechanisms involved in the initial activation of these hydrocarbons—fumarate addition and carboxylation—are discussed, along with key enzymes, including alkylsuccinate synthase and benzylsuccinate synthase. Syntrophic interactions are also considered, particularly in which archaea initiate the oxidation of short-chain alkanes (e.g., ethane and butane), with sulfate-reducing bacteria serving as terminal electron acceptors via sulfate reduction. The potential application of these anaerobic processes in bioremediation strategies for oil-contaminated marine sediments is discussed. This microbially mediated degradation may offer a complementary approach to aerobic methods, particularly in oxygen-limited environments. Understanding the activity of sulfate-reducing bacteria activity is relevant to several areas: the development of remediation techniques for anoxic zones, the assessment of methane emissions from marine sediments, the management of microbiologically influenced corrosion, and potential biotechnological applications. Current research directions include the study of syntrophic microbial consortia and the exploration of bioelectrochemical systems. Full article

Rare earth elements (REEs) play a critical role in provenance tracing and the environmental reconstruction of the Earth. However, systematic investigations into the geochemical behavior and fractionation mechanisms of REEs during halite crystallization in brine–salt systems remain limited. This study reports new trace element and REE data for Late Cretaceous halites from the Thakhek Basin, Laos. Ratios of Sr/Ba, Sr/Cu, and V/Cr indicate a marine origin for the halites, which formed under hot climatic and oscillating oxidizing–anoxic redox conditions. Both primary and secondary halites display uniform Post-Archean Australian Shale (PAAS)-normalized REE distribution patterns, characterized by relative enrichment in medium rare earth elements (MREE) and depletion in light (LREE) and heavy rare earth elements (HREE). Similar REE patterns are also observed in halites from other modern and ancient, continental and marine salt basins worldwide. These observations suggest that the influences of parent brine composition and external provenance supplies on REE fractionation are negligible, given the consistent source, salinity, and redox conditions recorded in these halites. Accordingly, REE fractionation in halite was largely controlled by crystallographic effects, with aqueous MREE preferentially incorporated into halite crystals during deposition. In addition, the relatively lower Zr/Hf ratios in secondary halites compared to primary halites further validate the utility of the Zr/Hf ratio for distinguishing authigenic halite from salt modified by diagenesis, weathering, dissolution, or recrystallization. While our results establish a fundamental REE distribution pattern for halite, further research is needed to better constrain the underlying fractionation mechanisms of REEs in evaporite minerals within brine–salt systems. Full article

Cervical cancer has a high incidence and mortality, and is one of the leading causes of cancer-related deaths among women worldwide. The infection with high-risk subtypes of the human papillomavirus (HPV) represents a crucial factor in the development of precancerous lesions. HPV oncoproteins target multiple host factors to promote uncontrolled cellular proliferation, genomic instability, profound metabolic reprogramming, resistance to apoptosis and immune evasion. Thus, cervical carcinogenesis involves metabolic reprogramming in patient cells, such as enhanced aerobic glycolysis, and altered glutamine, lipid and mitochondrial metabolism, which collectively support the bioenergetic and biosynthetic demands of cancer cells. Cancer cells also activate several mechanisms to adapt and survive under hypoxic/anoxic conditions. The mechanisms underlying cervical carcinogenesis often involve non-coding RNAs. This review aims at summarizing the mechanisms and factors involved in the development and progression of cervical cancer following HPV infection, and offers an overview of the available therapies that have been developed for this disease. Full article

European peatlands have been extensively drained for agriculture, resulting in substantial carbon losses and widespread soil degradation. Peatland restoration is therefore a global priority, with rewetting recognised as a key strategy for mitigating greenhouse gas emissions and climate change. This review synthesizes current knowledge on soil transformations following the rewetting of agriculturally drained peatlands in Europe. We describe major degradation processes induced by drainage, including land subsidence, organic matter oxidation, and microbial community shifts from anaerobic to aerobic conditions. We then examine key rewetting approaches—ditch blocking, controlled flooding, and paludiculture—and their intended restoration outcomes. Rewetting fundamentally alters soil physical, chemical, and biological properties by raising and stabilizing water tables, restoring anoxic conditions, and modifying nutrient cycling and microbial processes. Findings indicate long-term stabilization of organic carbon in peat soils under anaerobic conditions, but also reveal trade-offs between reduced CO₂ emissions and increased CH₄ and N₂O fluxes. Vegetation–soil interactions strongly influence recovery trajectories, and paludiculture offers potential to align agricultural land use with climate mitigation objectives. Finally, we evaluate current research methodologies and identify major knowledge gaps, including limited long-term data and insufficient integration of hydrological, chemical, and biological processes. We highlight priorities for future research to support evidence-based rewetting strategies that deliver climate benefits while maintaining ecological and economic sustainability in European peatlands. Full article

This study investigates the rare-earth element (REE) geochemistry of twenty-nine clastic rock samples from the Paleogene Liushagang Formation in the Weixi’nan Sag. The primary objectives were to quantitatively evaluate the depositional paleoenvironment, determine the provenance lithology, and constrain the tectonic setting of the source area. Results reveal distinct chondrite-normalized REE distribution patterns characterized by light REE (LREE) enrichment, relatively flat heavy REE (HREE) segments, and pronounced negative Eu anomalies. The cerium anomaly index (Ce_anom, normalized to the North American Shale Composite) ranges from −0.06 to 0.00, implying broadly suboxic to anoxic-reducing conditions in the water column during deposition. The chondrite-normalized (La/Yb)_N ratio, utilized as a proxy for relative depositional residence time, decreases stratigraphically from member 3 to member 1, reflecting a transition to shorter residence times and higher relative sedimentation rates. Laterally, (La/Yb)_N increases toward the basin center, accurately recording progressively lower sedimentation rates basinward. Provenance analysis indicates that the sediments were predominantly derived from felsic igneous rocks of the upper continental crust. Spatially, the northern steep-slope belt reflects a uniform source, whereas the southern gentle-slope belt and the Weixi’nan low-uplift periphery record multisource mixed inputs. Finally, tectonic discrimination reveals an “active continental margin” affinity. This geochemical signature represents the inherited tectonic environment of the Mesozoic parent rocks in the surrounding source uplifts, rather than the Cenozoic extensional rift setting of the Weixi’nan Sag itself. Full article

Marine shales of the Middle Ordovician Wulalike Formation in the Ordos Basin constitute a key target for shale gas exploration. However, the sedimentary environments associated with different shale lithofacies vary significantly, and the mechanisms controlling the organic matter enrichment remain incompletely understood. To address this issue, this study conducts a comprehensive analysis of the factors influencing organic matter enrichment in distinct lithofacies. Based on mineralogical and elemental geochemical data, Wulalike Formation shales can be grouped into three lithofacies associations (i.e., siliceous shales, calcareous shales, and mixed shales). Results indicate that the siliceous shale, with the highest TOC (avg. 1.05%), was deposited under a warm and humid climate with relatively high productivity and anoxic to euxinic bottom waters, promoting preservation. In contrast, the calcareous and mixed shales, formed under semihumid to semiarid climates with lower productivity and variable terrigenous input, exhibit lower TOC. Comprehensive analysis shows that, against the background of generally low organic matter abundance, organic matter enrichment were primarily associated with redox conditions and paleoclimate, with terrigenous input playing a dual role, while paleoproductivity had a limited effect. The overall lower TOC, compared to typical marine shales, may be attributed to deposition in a nutrient-limited, restricted, stagnant basin distal from volcanic sources. This study provides new insights into the organic matter enrichment mechanisms of Ordovician source rocks in the western Ordos Basin. Full article

The ocean constitutes the largest actively exchangeable carbon reservoir in Earth’s surface system, with the ocean–atmosphere system functioning as an integrated entity that modulates atmospheric CO₂ concentrations over geological timescales. While carbonate and organic-rich sedimentary carbon sinks have been the subject of extensive research, their synergistic roles in long-term carbon–climate feedback loops, as well as the degree to which microbial mediation links ocean hydrographic states to basin-scale carbon sequestration efficiency, remain poorly synthesized. Here, we develop a mechanistic framework comprising five intercoupled components: (1) driving factors (tectonic–climatic forcing and anthropogenic analogs); (2) ocean state controls (basin restriction, water column stratification, and redox conditions); (3) microbial processes (microbial carbon pump-mediated transformation of dissolved organic carbon and the modulating influence of microbial carbonate formation); (4) sedimentary carbon sinks (carbonate platforms versus organic-rich shales underpinning organo-mineral stabilization); and (5) Earth system feedback expressions (e.g., carbon isotope excursions and sustained perturbations in atmospheric CO₂ levels). This framework is validated across three contrasting sedimentary basins, including the Western Tethys rift basins, the Cambrian South China platform system, and the Toarcian Lower Saxony restricted basin, and via three falsifiable propositions. Converging evidence from these case studies corroborates three key conclusions: (1) basin restriction and diminished water mass renewal foster water column stratification and hypoxic/anoxic conditions, thereby enhancing organic carbon preservation (P1); (2) the tectonic and depositional setting of a basin modulates the relative predominance of carbonate and organic carbon sinks (P2); and (3) post-extinction anachronistic facies record amplified microbial control over carbon burial pathways (P3). By emphasizing the context dependence of carbon sequestration processes and the significance of organo-mineral stabilization alongside particulate organic carbon export, this synthesis provides a transferable analytical framework for interpreting deep-time carbon cycle transitions and for contextualizing the impacts of modern ocean warming and deoxygenation on natural carbon sinks. Full article

The second member of the Kongdian Formation (Ek₂; also referred to as the Kong 2 Member) in the Cangdong Sag within the Bohai Bay Basin contains a series of high-quality lacustrine shales characterized by high organic matter abundance and significant hydrocarbon shows. However, the mechanisms governing organic matter enrichment in the deep parts of the sag remain poorly understood, and the impacts of depositional environments on organic matter enrichment are yet to be determined. This study investigated shales in the C1, C3, and C5 sublayers of the Kong 2 Member. Specifically, this study examined the mineralogy and petrology, organic geochemistry, and elemental geochemistry of the shales using whole-rock X-ray diffraction (XRD) analysis, total organic carbon (TOC) analysis, pyrolysis experiments, and analyses of macerals, major and trace elements, and stable carbon and oxygen isotopes. Additionally, numerical analyses were conducted. The results indicate that shales in the Kong 2 Member consist primarily of felsic, dolomitic–calcareous, and mixed shales. These shales exhibit high TOC content (average: 3.07%), and favorable organic matter types dominated by liptinite and interbedded with minor planktonic algae and amorphous sapropelinite. These suggest great potential for hydrocarbon exploitation. During the deposition of shales in the Kong 2 Member, substantial terrigenous clasts were deposited at moderate rates under relatively arid climates characterized by frequently alternating dry and humid conditions. In this period, the anoxic to reducing depositional water bodies showed elevated salinity, resulting in saline-to-brackish water environments and moderate paleoproductivity. The organic matter enrichment of shales in the Kong 2 Member was jointly governed by paleoclimate dynamics, terrigenous input, and redox conditions, as demonstrated by multivariate analyses including the correlation analysis of depositional environmental factors, the univariate analysis of TOC content, gray relational analysis (GRA), and robust regression analysis. Two organic matter enrichment patterns were identified: (1) the preservation-dominated pattern under arid climates, governed by intense reducing environments, and (2) the productivity-driven pattern under humid climates, enhanced by terrestrial input. Full article

As an emerging wastewater treatment technology, the membrane-aerated biofilm reactor (MABR) process is increasingly being coupled with anaerobic anoxic aerobic (AAO) process. However, there is currently a lack of systematic research and clear consensus on which of these two arrangements is more significant in improving overall process efficiency in practical applications. This study established GPS-X models of the conventional AAO process and two AAO-MABRs (anoxic or aerobic) under different concentrations of influent and effluent water quality conditions, and systematically compared their effluent quality, operation cost and greenhouse gas emissions. The results indicate that, compared with the conventional AAO process, the AAO-MABR coupled process improved the denitrification rate by 37.46%~47.71% (Anoxic), reduced energy consumption by an average of 0.11 kWh/m³, and lowered the operating cost by 0.036 USD/m³. In terms of carbon emission intensity, the AAO-MABR process achieved an average reduction of 0.67 kgCO₂eq/m³. Notably, the AAO-MABR (Anoxic) configuration exhibited superior robustness under varying influent and effluent conditions, yielding the lowest average operational cost (0.047 USD/m³) and carbon intensity (0.61 kgCO₂eq/m³). This study provides a reference for the practical application of MABR process, especially for the upgrading of traditional AAO processes. Full article

Piggery farming is the largest source of livestock manure in South Korea, yet greenhouse gas (GHG) data from piggery wastewater treatment systems remain limited. This study quantified methane (CH₄) and nitrous oxide (N₂O) fluxes from a full-scale treatment facility to develop stage-, seasonal-, and diurnal-specific emission factors. Continuous laser-based monitoring using a PVC air-pool chamber was applied across raw wastewater storage, an anoxic nitrogen-conversion reactor, and strongly aerated nitrification units. Mean CH₄ fluxes ranged from 1.1 to 15.6 mg s⁻¹ m⁻² peaking in summer, while N₂O fluxes ranged from 0.01 to 17,971 mg s⁻¹ m⁻², with maxima in fall. Emissions were dominated by two functional zones: aerated basins where vigorous mixing enhanced CH₄ stripping, and an upstream anoxic reactor where oxygen instability and nitrite accumulation produced extreme N₂O peaks. Derived emission factors were 0.11 kg CH₄ head⁻¹ yr⁻¹ and 45.2 kg N₂O head⁻¹ yr⁻¹, equivalent to 3.1 and 12,300 kg CO₂-eq head⁻¹ yr⁻¹. CH₄ variability was controlled mainly by treatment stage and temperature, whereas N₂O was governed by internal redox conditions. These results refine emission factors for inventories and underscore the need for improved aeration stability and denitrification control to reduce GHG emissions from piggery wastewater systems. Full article

Artificial freshwater bodies receive elemental inputs and face environmental stressors, posing a risk of wetland pollution that could threaten ecological health. In such an inland backwater, its microbial diversity and functional potentials remain uncharacterized. Here, shotgun metagenomic sequencing was performed on environmental DNA samples collected from the Atoud Dam reservoir in southwestern Saudi Arabia. The taxonomic assignments of the sequencing reads identified Pseudomonadota and Actinomycetota as the dominant phyla, while the most prevalent species was Microcystis aeruginosa. Binning assembled contigs recovered 30 metagenome-assembled genomes representing 11 phyla, suggesting potentially novel bacterial taxa and metabolic functions. Functional analysis of gene-coding sequences identified genes associated with mobile genetic elements and xenobiotic biodegradation pathways as the main factors driving the spread of antibiotic resistance genes. Additionally, a community-wide analysis of enzyme-encoding genes involved in regulating the carbon, nitrogen, and sulfur cycles revealed significant annotation of denitrification and thiosulfate oxidation pathways under anoxic conditions, suggesting early signs of eutrophication and a potential risk of algal blooms. Overall, our study provides detailed insights into the genomic capabilities of the microbial community in this previously understudied ecosystem and establishes baseline data for future assessments of microbial biodiversity in other, less-explored ecosystems, thereby facilitating more effective biomonitoring and discovery. Full article

To clarify the organic matter enrichment regularity of Permian shales in the Kaijiang–Liangping Trough, as well as the differential characteristics of their reservoir lithology, mineral assemblage, and nanopore structure—and thereby provide a geological basis for the exploration and development of Permian marine shales in the eastern Sichuan Basin—core samples from different depths of the Wujiaping Formation and Dalong Formation in Well DY-1H were analyzed using a series of micro–nano technical research methods, including whole-rock X-ray diffraction, major/trace element analysis, conventional porosity-permeability measurement, high-pressure mercury intrusion porosimetry, nitrogen adsorption, and field emission scanning electron microscopy. Research finds that the Dalong Formation shale contains Type I organic matter with high abundance, whereas the Wujiaping Formation shale is dominated by Type II₂ organic matter. The Wujiaping Formation experienced stronger terrigenous input and higher weathering intensity, while the Dalong Formation was deposited under persistently anoxic conditions, in contrast to the frequent oxic–anoxic alternations in the Wujiaping Formation. Paleoproductivity indicators suggest higher productivity in the Dalong Formation than in the Wujiaping Formation. Mo/TOC ratios below 4.5 indicate deposition in a strongly restricted water body. Enrichment factors of multiple elements further support the enhanced paleoproductivity of the Dalong Formation. The Dalong Formation shale has higher contents of quartz and carbonate minerals, while the Wujiaping Formation shale has a higher content of clay minerals. The Wujiaping Formation shale is more developed with inorganic micropores, whereas the Dalong Formation shale is characterized by more developed organic nanopores. During the sedimentary period of the Dalong Formation shale, the paleoproductivity was high, the sedimentary waterbody had high reducibility and restriction, and the reservoir was well-developed with nanopores. The Dalong Formation is a more favorable interval for Permian shale gas exploration and development in the Kaijiang–Liangping Trough. Full article

The Upper Permian marine shale of the inter-platform basin in the Nanpanjiang Basin are rich in organic matter, widely distributed, and relatively thick, indicating abundant resource potential for hydrocarbon exploration. To clarify the sedimentary condition and the variability of reservoir properties, the paleo-environment was reconstructed by using geochemical, mineralogical, rock-property, and pore-structure data. Building on a lithofacies classification, the development patterns of different shale lithofacies were revealed. Reservoir characteristics among lithofacies were compared using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and low-temperature Nuclear Magnetic Resonance Cryoporometry (NMRC) experiments. A fractal analysis was performed based on NMR and NMRC data to quantify pore-scale heterogeneity, calculate fractal dimensions (D₁, D₂, and D_c), and evaluate the complexity of pore systems across lithofacies. Correlation analysis and redundancy analysis were applied to further explore the controlling factors of reservoir heterogeneity. The results showed that organic-rich shale in the Permian Linghao Formation occurred mainly in the 1st Member, with average total organic carbon (TOC) content of 2.57%, and the lower part of the 3rd Member (average TOC content 2.88%). In the 1st Member, high-carbon shale was deposited under humid conditions with intense weathering, abundant fine-grained clastic input from basin margins, strongly reducing (anoxic) bottom waters, vigorous phosphorus recycling, and moderate to low primary productivity. Using TOC and mineral composition, seven shale lithofacies were identified in the Linghao Formation, and their development patterns were established based on depositional paleo-environment characteristics and evolution. In the 1st Member, organic-rich shale was dominated by mixed lithofacies with moderate to high TOC. The paleo-environment exerted a primary control on reservoir properties, gas content, pore structure, and heterogeneity. The high-carbon lithofacies had the most favorable rock properties—higher porosity, greater pore volume, and higher gas content—and contained a larger proportion of well-developed organic pores. Fractal analysis revealed that seepage pores exhibited greater structural complexity than adsorption-related pores, with the high-carbon lithofacies showing the highest overall fractal dimensions and thus the strongest heterogeneity. Across the formation, higher clay content and TOC were the primary drivers of increased pore-scale heterogeneity, whereas greater feldspar and quartz contents tended to diminish it. Carbonates exerted a minor effect. Heterogeneity in adsorption pores exerted the strongest influence on differences among lithofacies. These results highlighted the utility of fractal analysis in quantitatively linking shale mineralogy and organic content to multiscale heterogeneity in inter-platform basin settings. Full article

The ability of plants to survive oxygen deficiency is associated with significant changes in metabolism. Metabolic profiling of wheat seedlings under anoxia and subsequent reoxygenation conditions was performed using GC-MS. A total of 374 and 298 compounds were detected in root and shoot metabolomes, respectively. All intermediates of central metabolism were identified. Early anoxic responses of root and shoot metabolomes showed similarity, leading to the accumulation of amino acids (Ala, GABA and Tyr), carboxylates (lactate and succinate), nucleotides and amines, together with a decrease in sugars. The metabolic response to long-term anoxia varied significantly in the roots and shoots of wheat seedlings and was related to the redistribution of carbon flux from glycolysis predominantly to lipids in the roots, while it was directed to carboxylates and GABA in the shoots. Imposition of 24 h of reaeration after short-term anoxia (6 h) switched the metabolome toward a normoxic profile, predominantly in roots. Anaerobically down-regulated metabolites were accumulated, while anaerobic intermediates were depleted post-anoxia. The effects of more prolonged anoxia on wheat seedling metabolomes were less reversible, particularly in shoots. Interestingly, several metabolites with not fully understood roles (e.g., hydroxyl carboxylates, α,ω-dicarboxylic acids, polyols) were detected under anoxic conditions in wheat seedlings, which could potentially serve as markers of plant sensitivity to oxygen deficiency. Full article