Biogeochemical Sulfur Cycle Research Articles

Microbial Diversity and Biogeochemical Cycling of Nitrogen and Sulfur in the Source Region of the Lancang River on the Tibetan Plateau

The Tibetan Plateau is known as the “third pole” on Earth, influencing regional and global climates and providing fresh water to billions of people. Climate change and anthropogenic activities are ...

Importance of extremophilic microorganisms in biogeochemical cycles

Extremophilic microorganisms are organisms capable of proliferating under extreme conditions that are generally detrimental to most life on Earth. They are organisms considered of importance in different areas of research, due to their ability to produce proteins and enzymes under inhospitable conditions. Therefore, in the present work, the information on their participation in the processes of biogeochemical cycles was collected and analyzed in order to demonstrate their ecological importance. Recent studies on the metabolic pathways of the Extremophilic microorganisms and their environment have shown that most of the archaea, some bacteria and cyanobacteria carry out metabolic activities essential for the biogeochemical cycles of sulfur, carbon and nitrogen. Archaea and bacteria being one of the main microorganisms that participate in a variety of processes such as sulfidogenesis, methanogenesis, ANAMMOX (anaerobic ammonium oxidation), among others. This has suggested that Extremophilic microorganisms and extreme ecosystems have a significant impact on global biogeochemical cycles.

An Emiliania huxleyi pan-transcriptome reveals basal strain specificity in gene expression patterns

Emiliania huxleyi is a cosmopolitan coccolithophore widespread in temperate oceans. This unicellular photoautotroph forms massive recurring blooms that play an important role in large biogeochemical cycles of carbon and sulfur, which play a role in climate change. The mechanism of bloom formation and demise, controlled by giant viruses that routinely infect these blooms, is poorly understood. We generated a pan-transcriptome of E. huxleyi, derived from three strains with different susceptibility to viral infection. Expression profiling of E. huxleyi sensitive and resistant strains showed major basal differences, including many genes that are induced upon viral infection. This suggests that basal gene expression can affect the host metabolic state and the susceptibility of E. huxleyi to viruses. Due to its ecological importance, the pan-transcriptome and its protein translation, applicable to many E. huxleyi strains, is a powerful resource for investigation of eukaryotic microbial communities.

Atmospheric Fate of the CH3SOO Radical from the CH3S + O2 Equilibrium.

The atmospheric oxidation mechanisms of reduced sulfur compounds are of great importance in the biogeochemical sulfur cycle. The CH3S radical represents an important intermediate in these oxidation processes. Under atmospheric conditions, CH3S will predominantly react with O2 to form the peroxy radical CH3SOO. The formed CH3SOO has two competing unimolecular reaction pathways: isomerization to CH3SO2, which further decomposes into CH3 and SO2, or a hydrogen shift followed by HO2 loss, leading to CH2S. Previous theoretical calculations have suggested that CH2S formation should be the dominant pathway, in disagreement with existing experimental results. Our large active space multireference configuration interaction calculations agree with the experimental results that the formation of CH3 and SO2 is the dominant route and the formation of CH2S and HO2 can, at most, be a minor pathway. We support the calculations with new experiments starting from the OH + CH3SH reaction for CH3S formation under low NOx conditions and find a SO2 yield of 0.86 ± 0.18 within our reaction time of 7.9 s. Model simulations of our experiments show that the SO2 yield converges to 0.98. This combined theoretical and experimental study thus furthers the understanding of the general oxidation mechanisms of sulfur compounds in the atmosphere.

Elevated particulate methanesulfonate, oxalate and iron over Sydney Harbour in the austral summer of 2019-20 during unprecedented bushfire activity

In the austral summer period, Dec 7, 2019 to Mar 1, 2020, which included unprecedented bushfire activity, total suspended particulate concentrations of methanesulfonate (MSA), oxalate, labile iron, SO42−, Cl−, Na+, K+, NH4+, water soluble solids (WSS) and water soluble organic carbon (WSOC) were measured from weekly filter samples at Seaforth on the northern edge of Sydney Harbour. Particle number concentrations (PNC) and meteorological conditions were also measured at hourly intervals. These entities were previously measured in the spring-summer period, Sep 30, 2018 to Feb 24, 2019. Data analysis is focussed on inter-comparison between the summer of 2018–19 (S1) and 2019–20 (S2) spanning the period 7 Dec to 24 Feb. During S2 seasonally averaged MSA, oxalate, labile iron, K+, PNC (0.5–2.5 μm), and WSOC were elevated by 102%, 57%, 64%, 72%, 108%, and 1907%, respectively, by comparison to S1. Aqueous phase secondary formation of oxalate and a marine source of MSA were evident during S1; however, during S2 it was indicated that the bushfires created conditions where oxalate formation was shifted away from aqueous phase processing and MSA became associated with bushfire generated WSOC aerosol. Correlation changes at the a = 0.05 significance level between S1 and S2 for MSA, and for oxalate, are examined and discussed in relation to effects apparently caused by the bushfires. It is indicated that the biogeochemical cycling of sulfur and carbon, and particulate deposition of iron micronutrient to the South Pacific Ocean, may be altered by bushfires in Australia.

Metagenomic and metabolic analyses of poly-extreme microbiome from an active crater volcano lake

El Chichón volcano is one of the most active volcanoes in Mexico. Previous studies have described its poly-extreme conditions and its bacterial composition, although the functional features of the complete microbiome have not been characterized yet. By using metabarcoding analysis, metagenomics, metabolomics and enzymology techniques, the microbiome of the crater lake was characterized in this study. New information is provided on the taxonomic and functional diversity of the representative Archaea phyla, Crenarchaeota and Euryarchaeota, as well as those that are representative of Bacteria, Thermotogales and Aquificae. With culture of microbial consortia and with the genetic information collected from the natural environment sampling, metabolic interactions were identified between prokaryotes, which can withstand multiple extreme conditions. The existence of a close relationship between the biogeochemical cycles of carbon and sulfur in an active volcano has been proposed, while the relationship in the energy metabolism of thermoacidophilic bacteria and archaea in this multi-extreme environment was biochemically revealed for the first time. These findings contribute towards understanding microbial metabolism under extreme conditions, and provide potential knowledge pertaining to "microbial dark matter", which can be applied to biotechnological processes and evolutionary studies.

Dissolved organic carbon drives nutrient cycling via microbial community in paddy soil

Microbial mediated iron cycling drives the biogeochemical cycling of carbon, nitrogen, sulfur, and phosphorus. However, the fate of the microbial community and the relative metabolic pathways in paddy soil after the addition of biogas slurry are poorly understood. In this study, the response of functional genes was investigated by growing one-season rice in paddy soils in a pot experiment. Seven treatments were prepared: 1) control (CK); 2) organic carbon (OC); 3) fertilizer (F); 4) 5% of biogas slurry (B05); 5) 10% of biogas slurry (B10); 6) 15% of biogas slurry (B15); 7) 20% of biogas slurry (B20). In the biogas slurry treatments, Geobacter increased more than in the other treatments during rice growth, which were structured by TOC. Particularly, in the B10 treatment, the relative abundance of Geobacter was 1.6 and 14.8 times higher than that of CK at the heading and mature stages, respectively. At the heading stage, the addition of biogas slurry and OC shifted the microbial phosphorus-transformation communities differently. There were no significant differences in the carbon, nitrogen, and sulfur metabolic pathways between the two treatments. At the mature stage, the carbon: nitrogen: phosphorus balance was significantly influenced by the regulation of functional gene expression and metabolic activities. These findings provide insight into the key factors affecting carbon, nitrogen, sulfur, phosphorus, and iron during rice growth after carbon inputs.

Quadruple sulfur isotope biosignatures from terrestrial Mars analogue systems

In this study, we present quadruple sulfur isotope values (QSI: 32S,33S,34S,36S) measured in sediments from two sulfur-rich Mars analogue environments: i) the glacially-fed hydrothermal pools in Iceland (Kerlingarfjöll and Kverkfjöll), and ii) the Lost Hammer hypersaline spring from Axel Heiberg Island, Nunavut, Canada. The localities host different physical and geochemical characteristics, including aqueous geochemistry, volcanic input, temperature, pH and salinity. The δ34S values of sulfur compounds from the Lost Hammer hypersaline spring exhibit large fractionations typical of microbial sulfate reduction (MSR) with or without additional oxidative sulfur cycling and microbial sulfur disproportionation (MSD) (34εSO4-CRS from −49.5 to −43.5‰), contrary to the small S isotope fractionations reported for the Icelandic hydrothermal sites (34εSO4-CRS from −9.9 to −0.7‰). Lost Hammer minor S isotope values (Δ33S and Δ36S), interpreted within the context of a sulfur cycling box model, are consistent with a biogeochemical S cycle including both MSR and MSD. In contrast, the small range in δ34S values within the Iceland hydrothermal pools are consistent with a large volcanic H2S flux and minimal biological S cycling. The minor S isotope values recorded in the hydrothermal pools, however, indicate further biogeochemical sulfur cycling. Our results demonstrate that contrasting physical and chemical characteristics between sites support different microbial S cycling processes, as recorded in the QSI sedimentary values. The QSI data and the derived models support the strong potential for QSI values to be used as biosignatures in the search for life in Martian S-rich environments. These results also suggests that extreme, metabolic energy-limited environments with low abiotic sulfur fluxes could be more likely to produce unequivocal biological QSI signals than those with more moderate conditions or abundant available energy. This finding carries significant implications for targeting sites on Mars for in situ measurements or future sample return missions.

Enhanced sulfidization in a sedimentary turbidite layer from the Nansha Trough in the southern South China Sea

Microbial sulfate reduction occurs in diverse depositional sedimentary environments, especially in fine-grained sedimentary turbidites. However, the extent to which turbidites impact the mechanism of sulfidization and the carbon–sulfur–iron cycle is poorly understood. Here, a sediment gravity core (10GC) with 50-cm thick turbidites was collected from the Nansha Trough of the southwestern South China Sea (SSCS) to unravel the biogeochemistry and sulfidization processes. One accelerator mass spectrometric 14C date in the planktonic foraminifera indicates that the turbidite layer was deposited at or immediately before 16 ka. Using a suite of elemental (Fe, K, Si Al, and Zr) and sediment grain size proxies suggests that the sediments within the turbidites were derived from the Sunda Shelf and the Malay Peninsula. The TOC/TN values (9–20) of the turbidites indicate deposition of terrestrial organic matter with a mixture of C3 and C4 types of vegetation. The relatively negative 13CTIC values (−7.76‰ to 2.09‰) are robust evidence for the accumulation of authigenic carbonates, which was attributed to organoclastic sulfate reduction. The rather positive δ34SCRS (CRS: chromium reducible sulfur) (−37.5‰ to −10.5‰) and high CRS contents of the turbidites compared to the hemipelagic sediments suggest that the enhanced sulfidization occurred due to a high rate of sulfate reduction in the closed system. In contrast to the turbidites, the more negative δ34SCRS values (−50.9‰ to −47.4‰) in the hemipelagic sediments reflect early diagenetic pyritization at the sediment–water interface. This study highlights the importance of turbidite sedimentation on the biogeochemical cycling of sulfur, carbon, and iron. However, further research is needed to better understand and quantify the contribution of marine turbidite sediments to the global ocean C–S–Fe cycle.

Quantifying pyrite oxidation on continental shelves during the onset of Antarctic glaciation in the Eocene-Oligocene transition

The Eocene-Oligocene transition (EOT) is characterized by a global cooling trend, falling sea levels, and the onset of Antarctic glaciation. Previous studies investigate the interactions and feedbacks between ocean circulation, weathering, and atmospheric CO2 levels during this time. Here we explore the role of biogeochemical sulfur cycling, and report seawater sulfate isotope data across the EOT. Our data show that seawater sulfate δ34S and δ18OSO4 values decline by 0.6‰ and 1.5‰, respectively, between 34.5 and 33 Ma. Quantitative modeling suggests that approximately 8,000 Gt of the sulfide previously stored in shelf sediments has been reoxidized and transferred to the marine sulfate pool. This reoxidation process proceeds through reactions similar to those associated with acid mine drainage, generating 24,500 Gt sulfuric acid. These numbers are of similar magnitude as those estimated for Pleistocene glaciations and must have affected marine pH and/or alkalinity.

Molybdenum isotope composition of seep carbonates – Constraints on sediment biogeochemistry in seepage environments

Methane seepage causes significant changes in the local diagenetic environment and impacts the marine sedimentary cycles of sulfur, carbon, and molybdenum (Mo), which are intimately linked to each other. Molybdenum isotopic compositions were determined for authigenic carbonate nodules and bulk sediments of a 230-m long sediment core collected at a methane seep site in the South China Sea. Authigenic carbonate nodules occur at different sediment depths and display low δ13C values around −50‰ revealing that carbon predominantly derived from biogenic methane. Moreover, seep carbonate nodules are substantially enriched in Mo (Al-normalized enrichment factors MoEF between 27 and 70), and display nearly constant δ98Mo values around an average of +1.9‰ (relative to NIST3134 = +0.25‰), close to the Mo isotopic composition of modern seawater (+2.3‰). Linear positive correlations between δ98Mo values and pyrite sulfur contents and Mo contents were identified for seep carbonate samples. This implies that Mo scavenging into pyrite is likely controlled by hydrogen sulfide availability derived from sulfate-driven anaerobic oxidation of methane (SD-AOM). The essentially constant and high δ98Mo values suggest that Mo species were nearly quantitatively incorporated into the authigenic carbonates under highly sulfidic conditions, probably at times when the sulfate-methane transition zones (SMTZ) was situated at shallow sediment depth at times of high seepage activity. In contrast, bulk sediments that exhibit typical marine δ13C values close to 0‰ (versus VPDB), hence devoid of methane-derived seep carbonates, are characterized by low Mo contents (MoEF = ~0.9). Their lower δ98Mo values mostly ranging from +0.2 to +0.8‰, in accord with low Mo contents, likely reflect input of detrital Mo. Bulk sediments bearing seep carbonate nodules display variable δ13C values lower than −5‰ and are characterized by a wide range in Mo contents (MoEF from 1.5 to 45.3) and δ98Mo values (+0.7 to +3.0‰). The high δ98Mo values of some sediment samples, relative to the seep carbonate signature, might indicate an additional accumulation of a 98Mo enriched pool of molybdenum during later SD-AOM at a deeper SMTZ postdating initial seep carbonate formation; such 98Mo enrichment was probably caused by preceding preferential removal of lighter Mo isotopes from pore fluids. Our results indicate that Mo isotope systematics of seep deposits can provide constraints on the dynamics of the biogeochemical cycling of carbon, sulfur, and trace elements in methane seep environments. A potential for authigenic carbonates to archive the Mo isotopic composition of seawater is indicated, but will have to be assessed in future studies.

Using multi-proxy approach to constrain temporal variations of methane flux in methane-rich sediments of the southern South China Sea

Methane seeps are widespread on the seafloor in continental margins. However, the responses of methane flux and diagenetic processes at cold seeps to drastic environmental changes in the geological history are still poorly understood. Here, we report the geochemical composition of porewaters and sediments in a sediment core (CL3A) collected from methane-rich sediments in the southern South China Sea, in order to assess the variations in upward methane flux since the last glacial period. A sediment horizon at depths of ca. 510–660 cm below seafloor just above the current sulfate-methane transition zone (SMTZ) is identified, which shows geochemical anomalies including high total inorganic carbon (TIC) and total sulfur (TS) contents, extremely negative δ13CTIC values and positive sulfur isotopic ratios of acid insoluble sulfur (δ34Sacid-insoluble). We propose that the diagenetic records of sulfate-driven anaerobic oxidation of methane within a paleo-SMTZ were recorded by the accumulation of authigenic carbonate and iron sulfide within this zone. Such geochemical pattern implies a fixation of the SMTZ at a certain depth for a prolonged time, which is estimated as ~13,000 years. The stagnation of the SMTZ is probably attributed to a large decline in sedimentation rate during the transition of last glacial/interglacial period, which is supported by the 14C ages throughout the core. Moreover, a non-steady-state modelling for the concave-up depth profiles of porewater species suggests that a recent enhancement in upward methane flux has lasted for at least 550 years. In summary, this study suggests that the fixation of SMTZ during the glacial/interglacial transitions in dynamic sedimentation regimes can lead to the accumulation of large amount of authigenic carbonate and iron sulfide in continental margins and should be considered in global carbon and sulfur biogeochemical cycles.

Prophage Genomics and Ecology in the Family Rhodobacteraceae.

Roseobacters are globally abundant bacteria with critical roles in carbon and sulfur biogeochemical cycling. Here, we identified 173 new putative prophages in 79 genomes of Rhodobacteraceae. These prophages represented 1.3 ± 0.15% of the bacterial genomes and had no to low homology with reference and metagenome-assembled viral genomes from aquatic and terrestrial ecosystems. Among the newly identified putative prophages, 35% encoded auxiliary metabolic genes (AMGs), mostly involved in secondary metabolism, amino acid metabolism, and cofactor and vitamin production. The analysis of integration sites and gene homology showed that 22 of the putative prophages were actually gene transfer agents (GTAs) similar to a GTA of Rhodobacter capsulatus. Twenty-three percent of the predicted prophages were observed in the TARA Oceans viromes generated from free viral particles, suggesting that they represent active prophages capable of induction. The distribution of these prophages was significantly associated with latitude and temperature. The prophages most abundant at high latitudes encoded acpP, an auxiliary metabolic gene involved in lipid synthesis and membrane fluidity at low temperatures. Our results show that prophages and gene transfer agents are significant sources of genomic diversity in roseobacter, with potential roles in the ecology of this globally distributed bacterial group.

Iron and sulfur cycling in the cGENIE.muffin Earth system model (v0.9.21)

Abstract. The coupled biogeochemical cycles of iron and sulfur are central to the long-term biogeochemical evolution of Earth's oceans. For instance, before the development of a persistently oxygenated deep ocean, the ocean interior likely alternated between states buffered by reduced sulfur (“euxinic”) and buffered by reduced iron (“ferruginous”), with important implications for the cycles and hence bioavailability of dissolved iron (and phosphate). Even after atmospheric oxygen concentrations rose to modern-like values, the ocean episodically continued to develop regions of euxinic or ferruginous conditions, such as those associated with past key intervals of organic carbon deposition (e.g. during the Cretaceous) and extinction events (e.g. at the Permian–Triassic boundary). A better understanding of the cycling of iron and sulfur in an anoxic ocean, how geochemical patterns in the ocean relate to the available spatially heterogeneous geological observations, and quantification of the feedback strengths between nutrient cycling, biological productivity, and ocean redox requires a spatially resolved representation of ocean circulation together with an extended set of (bio)geochemical reactions. Here, we extend the “muffin” release of the intermediate-complexity Earth system model cGENIE to now include an anoxic iron and sulfur cycle (expanding the existing oxic iron and sulfur cycles), enabling the model to simulate ferruginous and euxinic redox states as well as the precipitation of reduced iron and sulfur minerals (pyrite, siderite, greenalite) and attendant iron and sulfur isotope signatures, which we describe in full. Because tests against present-day (oxic) ocean iron cycling exercises only a small part of the new code, we use an idealized ocean configuration to explore model sensitivity across a selection of key parameters. We also present the spatial patterns of concentrations and δ56Fe and δ34S isotope signatures of both dissolved and solid-phase Fe and S species in an anoxic ocean as an example application. Our sensitivity analyses show that the first-order results of the model are relatively robust against the choice of kinetic parameter values within the Fe–S system and that simulated concentrations and reaction rates are comparable to those observed in process analogues for ancient oceans (i.e. anoxic lakes). Future model developments will address sedimentary recycling and benthic iron fluxes back to the water column, together with the coupling of nutrient (in particular phosphate) cycling to the iron cycle.

Glycyl Radical Enzymes and Sulfonate Metabolism in the Microbiome.

Sulfonates include diverse natural products and anthropogenic chemicals and are widespread in the environment. Many bacteria can degrade sulfonates and obtain sulfur, carbon, and energy for growth, playing important roles in the biogeochemical sulfur cycle. Cleavage of the inert sulfonate C-S bond involves a variety of enzymes, cofactors, and oxygen-dependent and oxygen-independent catalytic mechanisms. Sulfonate degradation by strictly anaerobic bacteria was recently found to involve C-S bond cleavage through O2-sensitive free radical chemistry, catalyzed by glycyl radical enzymes (GREs). The associated discoveries of new enzymes and metabolic pathways for sulfonate metabolism in diverse anaerobic bacteria have enriched our understanding of sulfonate chemistry in the anaerobic biosphere. An anaerobic environment of particular interest is the human gut microbiome, where sulfonate degradation by sulfate- and sulfite-reducing bacteria (SSRB) produces H2S, a process linked to certain chronic diseases and conditions.

Isotopically “heavy” pyrite in marine sediments due to high sedimentation rates and non-steady-state deposition

AbstractSedimentary pyrite formation links the global biogeochemical cycles of carbon, sulfur, and iron, which, in turn, modulate the redox state of the planet's surficial environment over geological time scales. Accordingly, the sulfur isotopic composition (δ34S) of pyrite has been widely employed as a geochemical tool to probe the evolution of ocean chemistry. Characteristics of the depositional environment and post-depositional processes, however, can modify the δ34S signal that is captured in sedimentary pyrite and ultimately preserved in the geological record. Exploring sulfur and iron diagenesis within the Bornholm Basin, Baltic Sea, we find that higher sedimentation rates limit the near-surface sulfidization of reactive iron, facilitating its burial and hence the subsurface availability of reactive iron for continued and progressively more 34S-enriched sediment-hosted pyrite formation (δ34S ≈ −5‰). Using a diagenetic model, we show that the amount of pyrite formed at the sediment-water interface has increased over the past few centuries in response to expansion of water-column hypoxia, which also impacts the sulfur isotopic signature of pyrite at depth. This contribution highlights the critical role of reactive iron in pyrite formation and questions to what degree pyrite δ34S values truly reflect past global ocean chemistry and biogeochemical processes. This work strengthens our ability to extract local paleoenvironmental information from pyrite δ34S signatures.

Influence of Temperature and Sulfate Concentration on the Sulfate/Sulfite Reduction Prokaryotic Communities in the Tibetan Hot Springs.

The distribution and diversity of sulfate/sulfite reduction prokaryotic (SRP) communities in hot springs from the Quzhuomu and Daggyai Geothermal Zone of Tibetan, China, was reported for the first time. In hot springs that are naturally hyperthermal and anoxic, the sulfur cycle is one of the most active cycles of the elements. The distribution of SRP in response to temperature is of great importance to the understanding of biogeochemical cycling of sulfur in geothermal features. Little is known about the SRP in geothermal zone. In this study, the diversity of SRP was investigated in the sediments from the Daggyai and Quzhuomu geothermal zone using PCR amplification, cloning and sequencing of the dissimilatory sulfite reductase beta subunit gene (dsrB). The abundance of dsrB and 16S rRNA genes, were determined by quantitative polymerase chain reactions. In addition, correlations of the SRP assemblages with environmental factors were analyzed by the aggregated boosted tree (ABT) statistical analysis. The results showed that SRP populations were diverse, but were mainly composed of Desulfobacterales, Desulfovibrionales, Syntrophobacterales, Clostridia and Nitrospirales, and large fraction (25%) of novel sequences have branched groups in the dsrB phylogenetic tree. In Quzhuomu geothermal zone, sulfate-rich hot springs are characterized by thick bacterial mats that are green or red and the SRP populations mainly appear at mid-temperature (50 °C to 70 °C). In low-sulfate hot springs in the Daggyai geothermal zone, although gray or pink streamers are widely formed at 60 °C to 80 °C, they prefer to inhabit in green mat at lower temperature (30 °C to 50 °C). With increasing temperature, the diversity of the dsrB gene at the OTU level (cutoff 97%) decreased, while its relative abundance increased. This result suggests that temperature played an important role in affecting dsrB gene distribution.

Carbohydrate-dependent sulfur respiration in halo(alkali)philic archaea.

Archaea are environmentally ubiquitous on Earth, and their extremophilic and metabolically versatile phenotypes make them useful as model systems for astrobiology. Here, we reveal a new functional group of halo(natrono)archaea able to utilize alpha-d-glucans (amylopectin, amylose and glycogen), sugars, and glycerol as electron donors and carbon sources for sulfur respiration. They are facultative anaerobes enriched from hypersaline sediments with either amylopectin, glucose or glycerol as electron/carbon sources and elemental sulfur as the terminal electron acceptor. They include 10 strains of neutrophilic haloarchaea from circum pH-neutral lakes and one natronoarchaeon from soda-lake sediments. The neutrophilic isolates can grow by fermentation, although addition of S0 or dimethyl sulfoxide increased growth rate and biomass yield (with a concomitant decrease in H2 ). Natronoarchaeal isolate AArc-S grew only by respiration, either anaerobically with S0 or thiosulfate as the terminal electron acceptor, or aerobically. Through genome analysis of five representative strains, we detected the full set of enzymes required for the observed catabolic and respiratory phenotypes. These findings provide evidence that sulfur-respiring haloarchaea partake in biogeochemical sulfur cycling, linked to terminal anaerobic carbon mineralization in hypersaline anoxic habitats. We discuss the implications for life detection in analogue environments such as the polar subglacial brine-lakes of Mars.

Genomic evidence for sulfur intermediates as new biogeochemical hubs in a model aquatic microbial ecosystem

BackgroundThe sulfur cycle encompasses a series of complex aerobic and anaerobic transformations of S-containing molecules and plays a fundamental role in cellular and ecosystem-level processes, influencing biological carbon transfers and other biogeochemical cycles. Despite their importance, the microbial communities and metabolic pathways involved in these transformations remain poorly understood, especially for inorganic sulfur compounds of intermediate oxidation states (thiosulfate, tetrathionate, sulfite, polysulfides). Isolated and highly stratified, the extreme geochemical and environmental features of meromictic ice-capped Lake A, in the Canadian High Arctic, provided an ideal model ecosystem to resolve the distribution and metabolism of aquatic sulfur cycling microorganisms along redox and salinity gradients.ResultsApplying complementary molecular approaches, we identified sharply contrasting microbial communities and metabolic potentials among the markedly distinct water layers of Lake A, with similarities to diverse fresh, brackish and saline water microbiomes. Sulfur cycling genes were abundant at all depths and covaried with bacterial abundance. Genes for oxidative processes occurred in samples from the oxic freshwater layers, reductive reactions in the anoxic and sulfidic bottom waters and genes for both transformations at the chemocline. Up to 154 different genomic bins with potential for sulfur transformation were recovered, revealing a panoply of taxonomically diverse microorganisms with complex metabolic pathways for biogeochemical sulfur reactions. Genes for the utilization of sulfur cycle intermediates were widespread throughout the water column, co-occurring with sulfate reduction or sulfide oxidation pathways. The genomic bin composition suggested that in addition to chemical oxidation, these intermediate sulfur compounds were likely produced by the predominant sulfur chemo- and photo-oxidisers at the chemocline and by diverse microbial degraders of organic sulfur molecules.ConclusionsThe Lake A microbial ecosystem provided an ideal opportunity to identify new features of the biogeochemical sulfur cycle. Our detailed metagenomic analyses across the broad physico-chemical gradients of this permanently stratified lake extend the known diversity of microorganisms involved in sulfur transformations over a wide range of environmental conditions. The results indicate that sulfur cycle intermediates and organic sulfur molecules are major sources of electron donors and acceptors for aquatic and sedimentary microbial communities in association with the classical sulfur cycle.-hYdWkMRSgNRZXNRu4CdmLVideo abstract

Uncovering multi-faceted taxonomic and functional diversity of soil bacteriomes in tropical Southeast Asian countries

Environmental microbiomes encompass massive biodiversity and genetic information with a wide-ranging potential for industrial and agricultural applications. Knowledge of the relationship between microbiomes and environmental factors is crucial for translating that information into practical uses. In this study, the integrated data of Southeast Asian soil bacteriomes were used as models to assess the variation in taxonomic and functional diversity of bacterial communities. Our results demonstrated that there were differences in soil bacteriomes across different geographic locality with different soil characteristics: soil class and pH level. Such differences were observed in taxonomic diversity, interspecific association patterns, and functional diversity of soil bacteriomes. The bacterial-mediated biogeochemical cycles of nitrogen, sulfur, carbon, and phosphorus illustrated the functional relationship of soil bacteriome and soil characteristics, as well as an influence from bacterial interspecific interaction. The insights from this study reveal the importance of microbiome data integration for future microbiome research.