Biogeochemical Sulfur Cycle Research Articles

Microbial drivers of biogeochemical cycles in deep sediments of the Kathiawar Peninsula Gulfs of India.

Deep marine sediments are rich in microbial diversity, which holds metabolic repertoire to modulate biogeochemical cycles on a global scale. We undertook the environmental microbiome inhabiting the Gulf of Kathiawar Peninsula as a model system to understand the potential involvement of the deep marine sediment microbial community and as a cohort in the carbon, nitrogen, and sulfur biogeochemical cycles. These gulfs are characterized by dynamic tidal variations, diverse sediment textures, and nutrient-rich waters, driven by coastal processes and the interaction between natural coastal dynamics and anthropogenic inputs that shape its microbial community diversity. Our findings suggest that carbon fixation was carried out by Gamma-proteobacteria with CBB cycle-related genes or by microbial participants with Wood-Ljungdahl pathway-related genes. Microbial communities involved in nitrogen metabolism were observed to be rich and diverse, and most microbial communities potentially contribute to the nitrogen cycle via processing nitrogen oxides. Bacteria belonging to the KSB1 phylum were also found to fix nitrogen. The sulfur cycle was spread throughout, with Verrucomicrobiota phylum being a major contributor. The varying napAB genes, significantly lower in the Gulf of Kutch compared to the Gulf of Cambay and the Arabian Sea, mediated nitrate reduction. Dynamics between these pathways were mutually exclusive, and organic carbon oxidation was widespread across the microbial community. Finally, the proteobacteria phylum was highly versatile and conceivably contributed to biogeochemical flux with exceptionally high abundance and the ability to form metabolic networks to survive. The work highlights the importance of critical zones and microbial diversity therein, which needs further exploration.

Discovery of a Gut Bacterial Pathway for Ergothioneine Catabolism.

Ergothioneine is a diet-derived micronutrient for humans. However, enzymes involved in the catabolism of ergothioneine in human gut bacteria have not yet been identified. Herein, we characterize a sulfidogenic pathway for gut bacterial catabolism of this micronutrient, which involves an unprecedented reductive desulfurization reaction catalyzed by members of the xanthine oxidoreductase family (XOR), a class of molybdenum-containing flavoproteins. Notably, this is the first C-S bond cleavage reaction known to be catalyzed by XORs. Evidence for operation of this pathway was gained through in vitro reconstruction using heterologously produced enzymes derived from the human gut bacterium Blautia producta ATCC 27340. This catabolic activity enables B. producta ATCC 27340 to use ergothioneine as an alternative electron acceptor source. Homologues of the pathway enzymes are shown to be present not only in human gut bacteria but also in many environmental bacteria, suggesting the wide distribution of this catabolic strategy. In relation to the sulfur-containing metabolite, this discovery provides significant insight into biogeochemical sulfur cycling in diverse anoxic habitats beyond the human gut and, moreover, the design of new approaches for controlling intestinal hydrogen sulfide (H2S) production.

Microbiome dynamics and functional profiles in deep-sea wood-fall micro-ecosystem: insights into drive pattern of community assembly, biogeochemical processes, and lignocellulose degradation.

Wood-fall micro-ecosystems contribute to biogeochemical processes in the oligotrophic deep ocean. However, the community assembly processes and biogeochemical functions of microbiomes in wood fall remain unclear. This study investigated the diversity, community structure, assembly processes, and functional profiles of bacteria and fungi in a deep-sea wood fall from the South China Sea using physicochemical indices, amplicon sequencing, and metagenomics. The results showed that distinct wood-fall contact surfaces exhibit habitat heterogeneity. The bacterial community of all contact surfaces and the fungal community of seawater contact surface (SWCS) were affected by homogeneous selection. In SWCS and transition region (TR), bacterial communities were influenced by dispersal limitation, whereas fungal communities were affected by homogenizing dispersal. The Venn diagram visualization revealed that the shared fungal community between SWCS and TR was dominated by Aspergillaceae. Additionally, the bacterial community demonstrated a higher genetic potential for sulfur, nitrogen, and methane metabolism than fungi. The sediment contact surface enriched modules were associated with dissimilatory sulfate reduction and methanogenesis, whereas the modules related to nitrate reduction exhibited enrichment characteristics in TR. Moreover, fungi showed a stronger potential for lignocellulase production compared to bacteria, with Microascaceae and Nectriaceae identified as potential contributors to lignocellulose degradation. These results indicate that environmental filtering and organism exchange levels regulated the microbial community assembly of wood fall. The biogeochemical cycling of sulfur, nitrogen, and methane was mainly driven by the bacterial community. Nevertheless, the terrestrial fungi Microascaceae and Nectriaceae might degrade lignocellulose via the combined action of multiple lignocellulases.IMPORTANCEThe presence and activity of microbial communities may play a crucial role in the biogeochemical cycle of deep-sea wood-fall micro-ecosystems. Previous studies on wood falls have focused on the microbiome diversity, community composition, and environmental impact, while few have investigated wood-fall micro-ecosystems by distinguishing among distinct contact surfaces. Our study investigated the microbiome dynamics and functional profiles of bacteria and fungi among distinct wood-fall contact surfaces. We found that the microbiome community assembly was regulated by environmental filtering and organism exchange levels. Bacteria drive the biogeochemical cycling of sulfur, nitrogen, and methane in wood fall through diverse metabolic pathways, whereas fungi are crucial for lignocellulose degradation. Ultimately, this study provides new insights into the driving pattern of community assembly, biogeochemical processes, and lignocellulose degradation in the microbiomes of deep-sea wood-fall micro-ecosystems, enhancing our comprehension of the ecological impacts of organic falls on deep-sea oligotrophic environments.

Anaerobic Faecalicatena spp. degrade sulfoquinovose via a bifurcated 6-deoxy-6-sulfofructose transketolase/transaldolase pathway to both C2- and C3-sulfonate intermediates.

Plant-produced sulfoquinovose (SQ, 6-deoxy-6-sulfoglucose) is one of the most abundant sulfur-containing compounds in nature and its bacterial degradation plays an important role in the biogeochemical sulfur and carbon cycles and in all habitats where SQ is produced and degraded, particularly in gut microbiomes. Here, we report the enrichment and characterization of a strictly anaerobic SQ-degrading bacterial consortium that produces the C2-sulfonate isethionate (ISE) as the major product but also the C3-sulfonate 2,3-dihydroxypropanesulfonate (DHPS), with concomitant production of acetate and hydrogen (H2). In the second step, the ISE was degraded completely to hydrogen sulfide (H2S) when an additional electron donor (external H2) was supplied to the consortium. Through growth experiments, analytical chemistry, genomics, proteomics, and transcriptomics, we found evidence for a combination of the 6-deoxy-6-sulfofructose (SF) transketolase (sulfo-TK) and SF transaldolase (sulfo-TAL) pathways in a SQ-degrading Faecalicatena-phylotype (family Lachnospiraceae) of the consortium, and for the ISE-desulfonating glycyl-radical enzyme pathway, as described for Bilophila wadsworthia, in an Anaerospora-phylotype (Sporomusaceae). Furthermore, using total proteomics, a new gene cluster for a bifurcated SQ pathway was also detected in Faecalicatena sp. DSM22707, which grew with SQ in pure culture, producing mainly ISE, but also 3-sulfolacate (SL) 3-sulfolacaldehyde (SLA), acetate, butyrate, succinate, and formate, but not H2. We then reproduced the growth of the consortium with SQ in a defined co-culture model consisting of Faecalicatena sp. DSM22707 and Bilophila wadsworthia 3.1.6. Our findings provide the first description of an additional sulfoglycolytic, bifurcated SQ pathway. Furthermore, we expand on the knowledge of sulfidogenic SQ degradation by strictly anaerobic co-cultures, comprising SQ-fermenting bacteria and cross-feeding of the sulfonate intermediate to H2S-producing organisms, a process in gut microbiomes that is relevant for human health and disease.

Unraveling a Novel Formation Pathway of Hydroxymethanesulfonate (HMS) in the Marine Atmosphere

AbstractHydroxymethanesulfonate (HMS, CH2(OH)SO3−) is an important contributor to organosulfates with the potential to impact the biogeochemical sulfur cycle and global climate. However, its characteristics in the marine atmosphere have rarely been investigated. This study investigated the abundances of HMS over the Yellow and East China Seas based on island and cruise observations, showing weak seasonal variations but significant spatial patterns. Aerosol pH was diagnosed as the limiting factor governing the production rates of HMS via the traditional aqueous processing. However, the disparities between the theoretical formation rates and observed concentrations implied the possibility of a new formation mechanism for HMS. Strong correlations were found between methanesulfonate (MSA) and HMS, with machine learning simulation indicating MSA as the most pivotal contributor. Through the density functional theory calculations, HMS can be generated by gas‐phase organic reactions between the •OOCH2SO3H radical (formed from the isomerization of methylsulfonoxyl radical (CH3SO3•) and oxidation) and NO or CH3OO• radical, leading to the cogeneration of HMS and MSA. The HMS production rate via the gas phase process was 3.7–55 times larger than that of aqueous processing, which extends the understanding of formation mechanisms of atmospheric organosulfur compounds.

Sedimentary conditions of Jiujialu Formation in central Guizhou, south China, and implications for the transformation of lithium–rich claystones into karst bauxites

Lithium and aluminum are both important metals. Recent studies have found that lithium–rich claystone and karst bauxite deposits are often associated with each other, however, the mechanisms of transformation of lithium–rich claystone to karst bauxite is unclear. In this study, two representative fresh profiles were collected from the Jiujialu Formation (C1jj) in central Guizhou, and the pyrite and whole rock sulfur isotopes were studied. The results showed that the diameter of framboidal pyrite indicating poor homogeneity (standard deviation = 5.17), suggesting that the water column of the Jiujialu Formation was oxidized. The development of lithium–rich claystone/bauxite in the Jiujialu Formation occurred near the redox interface. The low δ34S–VCDT value of the whole rock (averaging –15.06 ‰, –33.72 ‰—1.64 ‰) and the presence of multiple generations of pyrite (eroded–annular pyrite) indicated the efficient biogeochemical cycling of sulfur in a fluctuating oxidizing environment. A small amount of samples exhibited heavier sulfur isotope characteristics, and the coexistence of tetrahedral framboidal pyrite and pentagonal octahedral framboidal pyrite indicated intermittent closed sedimentary environments in the Jiujialu Formation. The Si content of some clay minerals around the eroded–annular pyrite is significantly reduced, and the δ34S–VCDT value are significantly negatively correlated with inactive elements such as Al2O3, TiO2, Ta and Nb, these indicate that the efficient biogeochemical cycling of sulfur resulted in the production and consumption of H+ around the pyrite, and the transformation of high silicon–bearing clay minerals around the pyrite to low silicon–bearing clay minerals and aluminum minerals (e.g., diaspore), ultimately leading to lithium–rich claystone transformed into the karst bauxite. The occurrence of this process requires an oxidizing atmospheric environment, which may elucidate why karst-type bauxite is exclusively formed during the Phanerozoic when atmospheric oxygen levels were high.

Contrasting molecular structures and photooxidation behaviors between dissolved organic sulfur released from rice straw-biochar and aerobically decomposed rice straw

Photooxidation of dissolved organic sulfur (DOS) in soils and natural waters plays an important role in the sulfur biogeochemical cycle. However, the structural-dependent photoliabilities of DOS from different sources remain unclear. Here, the molecular structures and photooxidation behaviors of DOS in pyrogenic dissolved black matter (PyDOM) derived from rice straw-pyrolyzed biochar (referred to as PyDOM-S and considered to be representative of black carbon from prairie fires) were thoroughly characterized and compared with those of DOS in leached dissolved organic matter (LDOM) derived from aerobically decomposed rice straw (referred to as LDOM-S and considered to be generally representative of organic-rich horizons in soils and peats). The Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis revealed that both PyDOM-S and LDOM-S were, respectively, dominated by aliphatic (60.4 % and 41.1 %) and lignin-like compounds (35.1 % and 40.1 %), followed by minimal aromatic and polyaromatic compounds (2.8 % and 11.9 % in total). As demonstrated by the sulfur K-edge X-ray absorption near-edge structure (S-XANES) analysis, PyDOM-S consisted mainly of organosulfate (80.4 %) contrasting to the diversified and mingled reduced sulfurs (62.7 %) and oxidized sulfurs (37.3 %) of LDOM-S. Under simulated sunlight irradiation, 74 % of sulfur in PyDOM-S was photomineralized to sulfate within 24 h and totaling 89 % after 168 h, but only 9 % and 42 % for LDOM-S given the same periods of time, confirming the much faster photomineralization of PyDOM-S. After 168-h irradiation, almost all molecules in PyDOM-S disappeared, whereas a large proportion (44.2 %) of LDOM-S molecules (mainly aliphatic and lignin-like compounds) were photo-resistant. Furthermore, the photomineralization of PyDOM-S was mainly contributed by the final and complete oxidation of organosulfate to sulfate; however, the photooxidation of LDOM-S was dominated by the sequential oxidation of exocyclic sulfur and heterocyclic sulfur to organosulfate prior to releasing sulfate. These results highlight that pyrogenic-sourced PyDOM-S and diagenesis-derived LDOM-S exhibit contrasting photooxidation behaviors due to the associated distinct molecular structures.

Evaluation of biocorrosion, biofouling, and health risks in the two study locations in danube alluvium

Within conducted research the results of microbiological investigations on specific metabolic (phenotypic) groups of bacteria that play crucial roles in the biogeochemical cycling of iron, manganese, nitrogen, sulfur, and carbon are presented. These bacteria are also involved in the development of biocorrosion and biofouling processes, with some posing risks to public health. Utilizing results from applied biological activity reaction tests (BART tests), processed using specialized software, potential risks for the development of microbiologically mediated corrosion, biofouling, and health risks were calculated for seven wells within two oxic sites in the Danube alluvium – Vinci and Veliko Gradište, Serbia. Moderate to high corrosion risk was determined for all seven wells at both sites (CR=5.4). Microbiological fouling risk was very high in three out of the seven investigated wells (PR=8.10). Among the seven sites studied, one site stood out based on the calculated high value of health risk coefficient (HR=8.10). The research results provide new insights into the microbiological role in aging wells in oxic groundwater of the Danube alluvium. It is demonstrated that the physicochemical composition and chemical species such as minerals, organic matter, and the specific composition of microbial communities in the studied groundwater have the potential to stimulate biocorrosion and the formation of deposits and biofilms within well structures. In addition to biochemical analyses, hydrogeological characteristics of the analyzed area are presented to define the geological stratigraphy, for which specific microbiological transformations would be expected based on the obtained results.

Acidophilic sulphate-reducing bacteria: Diversity, ecophysiology, and applications.

Acidophilic sulphate-reducing bacteria (aSRB) are widespread anaerobic microorganisms that perform dissimilatory sulphate reduction and have key adaptations to tolerate acidic environments (pH <5.0), such as proton impermeability and Donnan potential. This diverse prokaryotic group is of interest from physiological, ecological, and applicational viewpoints. In this review, we summarize the interactions between aSRB and other microbial guilds, such as syntrophy, and their roles in the biogeochemical cycling of sulphur, iron, carbon, and other elements. We discuss the biotechnological applications of aSRB in treating acid mine drainage (AMD, pH <3), focusing on their ability to produce biogenic sulphide and precipitate metals, particularly in the context of utilizing microbial consortia instead of pure isolates. Metal sulphide nanoparticles recovered after AMD treatment have multiple potential technological uses, including in electronics and biomedicine, contributing to a cost-effective circular economy. The products of aSRB metabolisms, such as biominerals and isotopes, could also serve as biosignatures to understand ancient and extant microbial life in the universe. Overall, aSRB are active components of the sulphur and carbon cycles under acidic conditions, with potential natural and technological implications for the world around us.

Biogenic Sulfide-Mediated Iron Reduction at Low pH

Acid mine drainage (AMD) pollutes natural waters, but some impacted systems show natural attenuation. We sought to identify the biogeochemical mechanisms responsible for the natural attenuation of AMD. We hypothesized that biogenic sulfide-mediated iron reduction is one mechanism and tested this in an experimental model system. We found sulfate reduction occurred under acidic conditions and identified a suite of sulfate-reducing bacteria (SRB) belonging to the groups Desulfotomaculum, Desulfobacter, Desulfovibrio, and Desulfobulbus. Iron reduction was not detected in microcosms when iron-reducing bacteria or SRB were selectively inhibited. SRB also did not reduce iron enzymatically. Rather, the biogenic sulfide produced by SRB was found to be responsible for the reduction of iron at low pH. Addition of organic substrates and nutrients stimulated iron reduction and increased the pH. X-ray diffraction and an electron microprobe analysis revealed that the polycrystalline, black precipitate from SRB bioactive samples exhibited a greater diversity of iron chalcogenide minerals with reduced iron oxidation states, and minerals incorporating multiple metals compared to abiotic controls. The implication of this study is that iron reduction mediated by biogenic sulfide may be more significant than previously thought in acidic environments. This study not only describes an additional mechanism by which SRB attenuate AMD, which has practical implications for AMD-impacted sites, but also provides a link between the biogeochemical cycling of iron and sulfur.

Bacterial community and dissolved organic matter networks in urban river: The role of human influence

Human activities have significantly altered the biogeochemical cycles of carbon, nitrogen, and sulfur in aquatic ecosystems, leading to ecological problems.This study utilized 16S rRNA gene high-throughput sequencing and excitation-emission matrix parallel factor analysis (EEM-PARAFAC) to evaluate the bacterial community composition and dissolved organic matter structure in the upstream (less impacted) and downstream (severely impacted) sections of the river, with a focus on the interactions between bacterial diversity and dissolved organic matter (DOM) characteristics.Results indicated significant spatial diversity in bacterial communities, with a higher α-diversity upstream compared to the more polluted downstream sections. Environmental parameters, particularly total phosphorus (TP) and dissolved oxygen (DO), were found to significantly influence the distribution and composition of bacterial phyla through redundancy analysis. The pattern of bacterial community assembly has shifted from predominantly deterministic to predominantly stochastic as a result of human activities. The analysis of DOM through EEM-PARAFAC identified three main fluorescent components, reflecting varied sources and interactions with bacterial communities. Upstream, microbial activities predominantly contributed to autochthonous DOM, while downstream, increased inputs of allochthonous DOM from human activities were evident. Furthermore, the study revealed that through the introduction of various organic pollutants and nutrient loads that shift microbial metabolic functions towards increased degradation and transformation of complex organic compounds downstream. Structural equation modeling (SEM) revealed that upstream human activities primarily affected bacterial communities indirectly by altering DOM properties. In contrast, downstream activities had both direct and indirect effects due to higher pollutant loads and more complex environmental conditions. These interactions underline the profound effect of anthropogenic factors on riverine ecosystems and emphasize the importance of managing human impacts to preserve microbial biodiversity and water quality.

Coupled sulfur and nitrogen cycling at a catchment scale: insights from isotopic and molecular techniques

The biogeochemical cycles of nitrogen (N) and sulfur (S) play important roles in sustaining the Earth's ecosystem. However, their potential coupling process and underlying mechanisms in the nature remain unclear. Through joint applications of river water's isotopic compositions, isotope-pairing experiments, and molecular techniques, this study revealed the coupled N-S cycling processes at a catchment scale from both geochemical and biological perspectives. The river water's natural abundance isotopic compositions indicated that sulfide oxidation was an important source (67.0 ± 5.5 % in summer and 72.0 ± 5.5 % in winter) of riverine sulfate (SO42−). In addition, sulfide oxidation and NOx reduction (especially denitrification) were tightly coupled in summer but less significantly so in winter. However, the coupling of sulfide oxidation and dissimilatory nitrate reduction to ammonium (DNRA) could not be overlooked in winter. The 15N pairing experiments quantitatively showed that the high sulfide oxidation rates in summer (4.7 ± 2.3 mol/km2/h) were significantly associated with the denitrification. Metagenomics and qPCR analyses of the soils supported the isotopic interpretations, substantiating the metabolic potential and coexistence of bacterial denitrification, DNRA, and sulfide oxidation, which was more prevalent in summer. This study reveals comprehensive evidence that sulfide oxidation and NOx reduction are tightly coupled at the catchment scale, which provides a new perspective towards a better understanding of N-S cycling.

Novel Insights on Extracellular Electron Transfer Networks in the Desulfovibrionaceae Family: Unveiling the Potential Significance of Horizontal Gene Transfer.

Some sulfate-reducing bacteria (SRB), mainly belonging to the Desulfovibrionaceae family, have evolved the capability to conserve energy through microbial extracellular electron transfer (EET), suggesting that this process may be more widespread than previously believed. While previous evidence has shown that mobile genetic elements drive the plasticity and evolution of SRB and iron-reducing bacteria (FeRB), few have investigated the shared molecular mechanisms related to EET. To address this, we analyzed the prevalence and abundance of EET elements and how they contributed to their differentiation among 42 members of the Desulfovibrionaceae family and 23 and 59 members of Geobacteraceae and Shewanellaceae, respectively. Proteins involved in EET, such as the cytochromes PpcA and CymA, the outer membrane protein OmpJ, and the iron-sulfur cluster-binding CbcT, exhibited widespread distribution within Desulfovibrionaceae. Some of these showed modular diversification. Additional evidence revealed that horizontal gene transfer was involved in the acquiring and losing of critical genes, increasing the diversification and plasticity between the three families. The results suggest that specific EET genes were widely disseminated through horizontal transfer, where some changes reflected environmental adaptations. These findings enhance our comprehension of the evolution and distribution of proteins involved in EET processes, shedding light on their role in iron and sulfur biogeochemical cycling.

Structural and functional bacterial biodiversity in a copper, zinc and nickel amended bioreactor: shotgun metagenomic study

BackgroundAt lower concentrations copper (Cu), zinc (Zn) and nickel (Ni) are trace metals essential for some bacterial enzymes. At higher concentrations they might alter and inhibit microbial functioning in a bioreactor treating wastewater. We investigated the effect of incremental concentrations of Cu, Zn and Ni on the bacterial community structure and their metabolic functions by shotgun metagenomics. Metal concentrations reported in previous studies to inhibit bacterial metabolism were investigated.ResultsAt 31.5 μM Cu, 112.4 μM Ni and 122.3 μM Zn, the most abundant bacteria were Achromobacter and Agrobacterium. When the metal concentration increased 2 or fivefold their abundance decreased and members of Delftia, Stenotrophomonas and Sphingomonas dominated. Although the heterotrophic metabolic functions based on the gene profile was not affected when the metal concentration increased, changes in the sulfur biogeochemical cycle were detected. Despite the large variations in the bacterial community structure when concentrations of Cu, Zn and Ni increased in the bioreactor, functional changes in carbon metabolism were small.ConclusionsCommunity richness and diversity replacement indexes decreased significantly with increased metal concentration. Delftia antagonized Pseudomonas and members of Xanthomonadaceae. The relative abundance of most bacterial genes remained unchanged despite a five-fold increase in the metal concentration, but that of some EPS genes required for exopolysaccharide synthesis, and those related to the reduction of nitrite to nitrous oxide decreased which may alter the bioreactor functioning.

Cascading sulfur cycling in simulated oil sands pit lake water cap mesocosms transitioning from oxic to euxinic conditions

Base Mine Lake (BML), the first full-scale demonstration of oil sands tailings pit lake reclamation technology, is experiencing expansive, episodic hypolimnetic euxinia resulting in greater sulfur biogeochemical cycling within the water cap. Here, Fluid Fine Tailings (FFT)-water mesocosm experiments simulating the in situ BML summer hypolimnetic oxic-euxinic transition determined sulfur biogeochemical processes and their controlling factors. While mesocosm water caps without FFT amendments experienced limited geochemical and microbial changes during the experimental period, FFT-amended mesocosm water caps evidenced three successive stages of S speciation in ∼30 days: (S1) rising expansion of water cap euxinia from FFT to water surface; enabling (S2) rapid sulfate (SO42−) reduction and sulfide production directly within the water column; fostering (S3) generation and subsequent consumption of sulfur oxidation intermediate compounds (SOI). Identified key SOI, elemental S and thiosulfate, support subsequent SOI oxidation, reduction, and/or disproportionation processes in the system. Dominant water cap microbes shifted from methanotrophs and denitrifying/iron-reducing bacteria to functionally versatile sulfur-reducing bacteria (SRB) comprising sulfate-reducing bacteria (Desulfovibrionales) and SOI-reducing/disproportionating bacteria (Campylobacterales and Desulfobulbales). The observed microbial shift is driven by decreasing [SO42−] and organic aromaticity, with putative hydrocarbon-degrading bacteria providing electron donors for SRB. Comparison between unsterile and sterile water treatments further underscores the biogeochemical readiness of the in situ water cap to enhance oxidant depletion, euxinia expansion and establishment of water cap SRB communities aided by FFT migration of anaerobes. Results here identify the collective influence of FFT and water cap microbial communities on water cap euxinia expansion associated with sequential S reactions that are controlled by concentrations of oxidants, labile organic substrates and S species. This emphasizes the necessity of understanding this complex S cycling in assessing BML water cap O2 persistence.

Iron biogeochemical redox cycling dominantly controls cadmium availability in acidic paddy soils

Periodic redox condition changes in acidic paddy soils substantially induce the biogeochemical redox cycling, and consequently affect Cd availability. However, the underlying biogeochemical mechanisms of the complicated redox processes in paddy soil remain poorly understood. Thus, we investigated the dynamics of Cd fractions under anoxic (0–40 days) and oxic (40–55 days) conditions. The available Cd content was evaluated using the diffusive gradients in thin film (DGT) technique, and the results show it decreased from 6.3 μg L–1 to below 0.1 μg L–1 under anoxic conditions, but rapidly increased to 13.5 μg L–1 under oxic conditions. Both sequential extraction procedures and X-ray absorption spectroscopy (XAS) analyses found that majority of available Cd transformed to organic matter complex and Fe-Mn oxides fractions, rather than bounded with sulfides. The soil chemical properties further evaluated, and the correlation analysis and principal component analysis results suggested that the key factors in soils for the available Cd was the SO42–, pH, and surface site concentration. The reduction of SO42– could generate sulfides which may precipitate with dissolved Cd. The biogeochemical redox cycling of Fe/N/S determined the changes of soil pH and consequently influenced adsorption behavior of Cd. The breakdown of the soil aggregations changed the surface site concentration, which may affect the immobilization of Cd. A process-based kinetic model was established, and it found that iron biogeochemical redox cycling dominated the changes of soil pH, and thereby contributed to majority Cd retention by Fe-Mn oxides (34.4 %) and organic matter (33.7 %). In addition, sulfur biogeochemical redox cycling only contributed to 13.6 % of the total Cd contents, because of relatively low Cd solubility in contaminated soils and the competition with other cations for limited sulfides. The findings provide robust targets for interpreting the iron and sulfur biogeochemical processes for Cd availability and would be helpful for developing the precise and effective remediation strategies in Cd-contaminated soils.

A distinctive rare earth element signature for pyrite oxidation and glacial weathering

The application of rare earth elements (REE) and neodymium (Nd) isotopes to authigenic Fe-(oxyhydr)oxide phases leached from marine sediments can be used for reconstructing past ocean circulation and chemical weathering patterns on nearby continental landmasses. To explore the behaviour of REE during chemical weathering in glacial environments, we analyzed the authigenic fraction of glacimarine sediments from the continental shelf off northern Svalbard (Arctic Ocean), where the evolution of ice sheet dynamics since the last deglaciation is well constrained. Our results show that leached authigenic fractions in Svalbard sediments exhibit shale-normalized REE patterns characterized by anomalously high mid-REE enrichment relative to both light- and heavy-REE, as expressed by concavity index values (CI > 2.5) that significantly depart from typical REE signatures for leached fractions in marine and river sediments worldwide. Using a compilation of literature data, we provide compelling evidence that the occurrence of pronounced mid-REE enrichment in authigenic fractions of Svalbard marine sediments links to terrestrial oxidation of pyrite following glacial weathering. While future investigation will be required to further understand the detailed mechanism accounting for the observed REE decoupling and its link to pyrite oxidation, we propose that preferential dissolution of mid-REE-enriched rock-bearing minerals such as apatite following glacial erosion, sulfide weathering and subsequent release of sulfuric acid could release a distinctive REE signature in glacial surface environments. Our findings suggest that the use of authigenic REE in the sedimentary record could provide a means for tracing glacial weathering and associated biogeochemical sulfur and iron cycling across geological times.

Higher diversity of sulfur-oxidizing bacteria based on soxB gene sequencing in surface water than in spring in Wudalianchi volcanic group, NE China.

Sulfur-oxidizing bacteria (SOB) play a key role in the biogeochemical cycling of sulfur. To explore SOB diversity, distribution, and physicochemical drivers in five volcanic lakes and twosprings in the Wudalianchi volcanic field, China. This study analyzed microbial communities in samples via high-throughput sequencing of the soxB gene. Physical-chemical parameters were measured, and QIIME 2 (v2019.4), R, Vsearch, MEGA7, and Mothur processed the data. Alpha diversity indices and UPGMA clustering assessed community differences, while heat maps visualized intra-sample variations. Canoco 5.0 analyzed community-environment correlations, and NMDS, Adonis, and PcoA explored sample dissimilarities and environmental factor correlations. SPSS v.18.0 tested for statistical significance. The diversity of SOB in surface water was higher than in springs (more than 7.27 times). We detectedSOB affiliated to β-proteobacteria (72.3 %), α-proteobacteria (22.8 %), and γ-proteobacteria (4.2 %) distributedwidely in these lakes and springs. Rhodoferax and Cupriavidus were most frequent in all water samples, whileRhodoferax and Bradyrhizobium are dominant in surface waters but rare in springs. SOB genera in both habitatswere positively correlated. Co-occurrence analysis identified Bradyrhizobium, Blastochloris, Methylibium, andMetyhlobacterium as potential keystone taxa. Redundancy analysis (RDA) revealed positive correlations betweenSOB diversity and total carbon (TC), Fe2+, and total nitrogen (TN) in all water samples. The diversity and community structure of SOB in volcanic lakes and springs in the Wudalianchivolcanic group were clarified. Moreover, the diversity and abundance of SOB decreased with the variation of wateropenness, from open lakes to semi-enclosed lakes and enclosed lakes.

Electron Transfer in the Biogeochemical Sulfur Cycle.

Microorganisms are key players in the global biogeochemical sulfur cycle. Among them, some have garnered particular attention due to their electrical activity and ability to perform extracellular electron transfer. A growing body of research has highlighted their extensive phylogenetic and metabolic diversity, revealing their crucial roles in ecological processes. In this review, we delve into the electron transfer process between sulfate-reducing bacteria and anaerobic alkane-oxidizing archaea, which facilitates growth within syntrophic communities. Furthermore, we review the phenomenon of long-distance electron transfer and potential extracellular electron transfer in multicellular filamentous sulfur-oxidizing bacteria. These bacteria, with their vast application prospects and ecological significance, play a pivotal role in various ecological processes. Subsequently, we discuss the important role of the pili/cytochrome for electron transfer and presented cutting-edge approaches for exploring and studying electroactive microorganisms. This review provides a comprehensive overview of electroactive microorganisms participating in the biogeochemical sulfur cycle. By examining their electron transfer mechanisms, and the potential ecological and applied implications, we offer novel insights into microbial sulfur metabolism, thereby advancing applications in the development of sustainable bioelectronics materials and bioremediation technologies.

Undisclosed contribution of microbial assemblages selectively enriched by microplastics to the sulfur cycle in the large deep-water reservoir

The accumulation of microplastics in reservoirs due to river damming has drawn considerable attention due to their potential impacts on elemental biogeochemical cycling at the watershed scale. However, the effects of plastisphere communities on the sulfur cycle in the large deep-water reservoir remain poorly understood. Here, we collected microplastics and their surrounding environmental samples in the water and sediment ecosystems of Xiaowan Reservoir and found a significant spatiotemporal pattern of microplastics and sulfur distribution in this Reservoir. Based on the microbial analysis, plastic-degrading taxa (e.g., Ralstonia, Rhodococcus) involved in the sulfur cycle were enriched in the plastisphere of water and sediment, respectively. Typical thiosulfate oxidizing bacteria Limnobacter acted as keystone species in the plastisphere microbial network. Sulfate, oxidation reduction potential and organic matter drove the variations of the plastisphere. Environmental filtration significantly affected the plastisphere communities, and the deterministic process dominated the community assembly. Furthermore, predicted functional profiles related to sulfur cycling, compound degradation and membrane transport were significantly enriched in the plastisphere. Overall, our results suggest microplastics as a new microbial niche exert different effects in water and sediment environments, and provide insights into the potential impacts of the plastisphere on the sulfur biogeochemical cycle in the reservoir ecosystem.