Potential Sulfate Reduction Research Articles

Anaerobic <i>Thermodesulfovibrio</i> and Aerobic <i>Meiothermus</i> Coexist in Deep Thermal Water

Abstract—Research on the microorganisms inhabiting deep aquifers is based on sampling the water released from deep wells and is seldom concerned with the physicochemical processes of the water-rock system. The issue of metabolism of aerobic prokaryotes revealed in deep habitats by molecular techniques remains unclear. Cultivation is required for direct determination of relation of prokaryotes to oxygen. In the present work, aerobic and anaerobic bacteria, which were revealed in thermal radon baths of the Belokurikha resort by molecular techniques, were isolated. Profiling by the 16S rRNA gene revealed predominance of members of the Deionococcus-Thermus group belonging to the genus Meiothermus (17.6% reads) and considered strictly aerobic. Anaerobic sulfate-reducing Thermodesulfovibrio were also present in the sample. The habitat was characterized by reductive, alkaline conditions. Target-oriented cultivation revealed aerobically growing Meiothermus sp. 1165, which was closely related to Meiothermus cerbereus. An alkaliphilic anaerobic sulfate reducer Thermodesulfovibrio sp. 1176 was also isolated. The rate of sulfate reduction measured in the Belokurikha water using \({\text{Na}}_{{\text{2}}}^{{{\text{ 35}}}}{\text{S}}{{{\text{O}}}_{{\text{4}}}}\) yielded the value of 41.4 ± 1.06 µm Sred L–1 day–1, or 1.29 nmol S mL–1 day–1. Analysis of the genome of strain 1176 revealed the presence of various mechanisms responsible for its relative resistance to oxygen and oxidative stress, which included superoxide reductase, rubredoxin, a Fe-Mn family superoxide dismutase, a KatG catalase-peroxidase, and a cytochrome bd ubiquinol oxidase. The low redox potential and intense anaerobic sulfate reduction provide evidence for the generally reduced conditions in the Belokurikha deep horizons. Spatial separation of aerobes and anaerobes in the water-rock system, similar to the one occurring in the terrestrial microbial mats, may be hypothesized, as well as occurring of aerobic processes in microniches.

Biochar-pyrite bi-layer bioretention system for dissolved nutrient treatment and by-product generation control under various stormwater conditions

Bioretention system with modified media has been increasingly used to control dissolved nutrients in stormwater runoff. However, complicated removal processes and improper design have made most of them hardly achieve comprehensive dissolved nutrient removal and even show by-product generation problem, especially during extreme stormwater events. Here, a modified biochar-pyrite (FeS2) bi-layer bioretention system was developed and tested under various stormwater conditions with conventional sand-based and woodchip-based bioretention systems as controls. The modified system showed high stability and efficiency for dissolved nutrient treatment. The removal of dissolved organic nitrogen, ammonium, total dissolved nitrogen, and total dissolved phosphorus were 86.3–93.0%, 95.3–98.1%, 41.4–76.5%, and 69.7–88.2%, respectively. Stormwater conditions only influence nitrate removal which decreased with the increase of total received volume and increased with the extension of antecedent drying duration. Net sulfate and total iron generation were very low, less than 8 mg/L and 0.15 mg/L, respectively. Several microbiology, spectroscopy, and media related tests further demonstrated that the vadose zone and submerged zone showed synergy effects during operation. Biochar addition facilitated ammonium adsorption, nitrification, and in situ denitrification in the vadose zone. It also intercepted dissolved oxygen, which alleviated aerobic pyrite oxidation and created an anoxic condition for the submerged zone. Meanwhile, the pyrite-modified submerged zone achieved stable mixotrophic denitrification. The generated iron intermediate products further controlled phosphorus from both influent and vadose zone leaching into stable forms. Mixotrophic denitrification and potential sulfate reduction processes also reduce sulfate generation. Overall, the biochar-pyrite bi-layer bioretention is a highly promising technology for stormwater runoff treatment, with effective dissolved nutrient removal and minimal by-product generation in various stormwater conditions.

Capability for arsenic mobilization in groundwater is distributed across broad phylogenetic lineages.

Despite the importance of microbial activity in mobilizing arsenic in groundwater aquifers, the phylogenetic distribution of contributing microbial metabolisms is understudied. Groundwater samples from Ohio aquifers were analyzed using metagenomic sequencing to identify functional potential that could drive arsenic cycling, and revealed mechanisms for direct (i.e., Ars system) and indirect (i.e., iron reduction) arsenic mobilization in all samples, despite differing geochemical conditions. Analyses of 194 metagenome-assembled genomes (MAGs) revealed widespread functionality related to arsenic mobilization throughout the bacterial tree of life. While arsB and arsC genes (components of an arsenic resistance system) were found in diverse lineages with no apparent phylogenetic bias, putative aioA genes (aerobic arsenite oxidase) were predominantly identified in Methylocystaceae MAGs. Both previously described and undescribed respiratory arsenate reduction potential via arrA was detected in Betaproteobacteria, Deltaproteobacteria, and Nitrospirae MAGs, whereas sulfate reduction potential was primarily limited to members of the Deltaproteobacteria and Nitrospirae. Lastly, iron reduction potential was detected in the Ignavibacteria, Deltaproteobacteria, and Nitrospirae. These results expand the phylogenetic distribution of taxa that may play roles in arsenic mobilization in subsurface systems. Specifically, the Nitrospirae are a much more functionally diverse group than previously assumed and may play key biogeochemical roles in arsenic-contaminated ecosystems.

Metabolic potential of microbial communities from ferruginous sediments.

Ferruginous (Fe-rich, SO4 -poor) conditions are generally restricted to freshwater sediments on Earth today, but were likely widespread during the Archean and Proterozoic Eons. Lake Towuti, Indonesia, is a large ferruginous lake that likely hosts geochemical processes analogous to those that operated in the ferruginous Archean ocean. The metabolic potential of microbial communities and related biogeochemical cycling under such conditions remain largely unknown. We combined geochemical measurements (pore water chemistry, sulfate reduction rates) with metagenomics to link metabolic potential with geochemical processes in the upper 50 cm of sediment. Microbial diversity and quantities of genes for dissimilatory sulfate reduction (dsrAB) and methanogenesis (mcrA) decrease with increasing depth, as do rates of potential sulfate reduction. The presence of taxa affiliated with known iron- and sulfate-reducers implies potential use of ferric iron and sulfate as electron acceptors. Pore-water concentrations of acetate imply active production through fermentation. Fermentation likely provides substrates for respiration with iron and sulfate as electron donors and for methanogens that were detected throughout the core. The presence of ANME-1 16S and mcrA genes suggests potential for anaerobic methane oxidation. Overall our data suggest that microbial community metabolism in anoxic ferruginous sediments support coupled Fe, S and C biogeochemical cycling.

Preparation of a Novel Nano or Submicron Tourmaline Ceramic and Its Ability to Inhibit the Activity of the Sulfate-Reducing Bacterium

In this study, novel nano- or submicron-scale tourmaline bacteriostatic ceramics in which nano or submicron tourmaline is one of the central materials, together with nano-zinc oxide, are prepared using ion exchange and solid-phase synthesis techniques. The material is then examined with IR, XRD and XPS and is tested for the ability to inhibit the activity of the sulfate-reducing bacterium (SRB). The calcination temperature of the ceramic is 600 °C, and the main components are present at 11.17% for Si2p, 3.12% for Mo3d, 3.47% for Zn2p3, 2.86% for Mn2p and 2.35% for Cu2p. Additionally, the density of this material is 1.4-3.5 g/cm3, and its compressive strength exceeds 5.2 MPa, meeting the requirements of ceramic standards. Consequently, the bacteriostatic ceramic inhibits the activity of the sulfate-reducing bacterium effectively without inhibiting the removal of COD and NO3-. These results indicate that the sulfate-reducing bacterium maintains its functional metabolism, apart from its sulfate reduction potential, when using this bacteriostatic ceramic, thus achieving the goal of inhibiting the action of the sulfate-reducing bacterium.

Microbial Sulfate Reduction Potential in Coal-Bearing Sediments Down to ~2.5 km below the Seafloor off Shimokita Peninsula, Japan.

Sulfate reduction is the predominant anaerobic microbial process of organic matter mineralization in marine sediments, with recent studies revealing that sulfate reduction not only occurs in sulfate-rich sediments, but even extends to deeper, methanogenic sediments at very low background concentrations of sulfate. Using samples retrieved off the Shimokita Peninsula, Japan, during the Integrated Ocean Drilling Program (IODP) Expedition 337, we measured potential sulfate reduction rates by slurry incubations with 35S-labeled sulfate in deep methanogenic sediments between 1276.75 and 2456.75 meters below the seafloor. Potential sulfate reduction rates were generally extremely low (mostly below 0.1 pmol cm−3 d−1) but showed elevated values (up to 1.8 pmol cm−3 d−1) in a coal-bearing interval (Unit III). A measured increase in hydrogenase activity in the coal-bearing horizons coincided with this local increase in potential sulfate reduction rates. This paired enzymatic response suggests that hydrogen is a potentially important electron donor for sulfate reduction in the deep coalbed biosphere. By contrast, no stimulation of sulfate reduction rates was observed in treatments where methane was added as an electron donor. In the deep coalbeds, small amounts of sulfate might be provided by a cryptic sulfur cycle. The isotopically very heavy pyrites (δ34S = +43‰) found in this horizon is consistent with its formation via microbial sulfate reduction that has been continuously utilizing a small, increasingly 34S-enriched sulfate reservoir over geologic time scales. Although our results do not represent in-situ activity, and the sulfate reducers might only have persisted in a dormant, spore-like state, our findings show that organisms capable of sulfate reduction have survived in deep methanogenic sediments over more than 20 Ma. This highlights the ability of sulfate-reducers to persist over geological timespans even in sulfate-depleted environments. Our study moreover represents the deepest evidence of a potential for sulfate reduction in marine sediments to date.

Geomicrobiological Features of Ferruginous Sediments from Lake Towuti, Indonesia.

Lake Towuti is a tectonic basin, surrounded by ultramafic rocks. Lateritic soils form through weathering and deliver abundant iron (oxy)hydroxides but very little sulfate to the lake and its sediment. To characterize the sediment biogeochemistry, we collected cores at three sites with increasing water depth and decreasing bottom water oxygen concentrations. Microbial cell densities were highest at the shallow site—a feature we attribute to the availability of labile organic matter (OM) and the higher abundance of electron acceptors due to oxic bottom water conditions. At the two other sites, OM degradation and reduction processes below the oxycline led to partial electron acceptor depletion. Genetic information preserved in the sediment as extracellular DNA (eDNA) provided information on aerobic and anaerobic heterotrophs related to Nitrospirae, Chloroflexi, and Thermoplasmatales. These taxa apparently played a significant role in the degradation of sinking OM. However, eDNA concentrations rapidly decreased with core depth. Despite very low sulfate concentrations, sulfate-reducing bacteria were present and viable in sediments at all three sites, as confirmed by measurement of potential sulfate reduction rates. Microbial community fingerprinting supported the presence of taxa related to Deltaproteobacteria and Firmicutes with demonstrated capacity for iron and sulfate reduction. Concomitantly, sequences of Ruminococcaceae, Clostridiales, and Methanomicrobiales indicated potential for fermentative hydrogen and methane production. Such first insights into ferruginous sediments showed that microbial populations perform successive metabolisms related to sulfur, iron, and methane. In theory, iron reduction could reoxidize reduced sulfur compounds and desorb OM from iron minerals to allow remineralization to methane. Overall, we found that biogeochemical processes in the sediments can be linked to redox differences in the bottom waters of the three sites, like oxidant concentrations and the supply of labile OM. At the scale of the lacustrine record, our geomicrobiological study should provide a means to link the extant subsurface biosphere to past environments.

How methane feedback response influence redox processes in a tropical vertisol

It has been predicted that soil CH4 consumption potential will increase due to rise in concentration of atmospheric CH4. However, it is unclear how this altered activity of soil will influence soil biogeochemical processes. Experiments were carried out to examine the effect of CH4 feedback response on (1) CH4 consumption potential, (2) population dynamics of methanotrophs, and (3) reductive biogeochemical processes in a tropical vertisol. Soils of different CH4 consumption potentials were prepared by three CH4 feeding cycles. Soils were then incubated to determine terminal electron accepting process (TEAPs) comprising sequential reduction of terminal electron acceptors (NO3 −, Fe3+, SO4 2−, and CO2). Diversity of methanotrophs was estimated by terminal restriction fragment length polymorphism (TRFLP) targeting the pmoA gene. Methane feedback increased apparent CH4 consumption rate (k) from 0.49 to 1.09 μg CH4 consumed per gram of soil. Potential denitrification rate (PDR), potential iron reduction rate (PIR), potential sulfate reduction rate (PSR) increased with k (p < 0.0001). Abundance of methanotrophs and heterotrophs was positively and significantly correlated with k (p < 0.0001). Methane feedback cycle influenced composition of the methanotrophs community (p < 0.0001). Principal component analysis (PCA) explained 83.86 and 12.05 % of variation by first two components.

Kinetics of sulfate reduction and sulfide precipitation rates in sediments of a bar-built estuary (Pescadero, California)

The bar-built Pescadero Estuary in Northern California is a major fish rearing habitat, though recently threatened by near-annual fish kill events, which occur when the estuary transitions from closed to open state. The direct and indirect effects of hydrogen sulfide are suspected to play a role in these mortalities, but the spatial variability of hydrogen sulfide production and its link to fish kills remains poorly understood. Using flow-through reactors containing intact littoral sediment slices, we measured potential sulfate reduction rates, kinetic parameters of microbial sulfate reduction (Rmax, the maximum sulfate reduction rate, and Km, the half-saturation constant for sulfate), potential sulfide precipitation rates, and potential hydrogen sulfide export rates to water at four sites in the closed and open states. At all sites, the Michaelis–Menten kinetic rate equation adequately describes the utilization of sulfate by the complex resident microbial communities. We estimate that 94–96% of hydrogen sulfide produced through sulfate reduction precipitates in the sediment and that only 4–6% is exported to water, suggesting that elevated sulfide concentrations in water, which would affect fish through toxicity and oxygen consumption, cannot be responsible for fish deaths. However, the indirect effects of sulfide precipitates, which chemically deplete, contaminate, and acidify the water column during sediment re-suspension and re-oxidation in the transition from closed to open state, can be implicated in fish mortalities at Pescadero Estuary.

Genome-Resolved Metagenomic Analysis Reveals Roles for Candidate Phyla and Other Microbial Community Members in Biogeochemical Transformations in Oil Reservoirs.

ABSTRACTOil reservoirs are major sites of methane production and carbon turnover, processes with significant impacts on energy resources and global biogeochemical cycles. We applied a cultivation-independent genomic approach to define microbial community membership and predict roles for specific organisms in biogeochemical transformations in Alaska North Slope oil fields. Produced water samples were collected from six locations between 1,128 m (24 to 27°C) and 2,743 m (80 to 83°C) below the surface. Microbial community complexity decreased with increasing temperature, and the potential to degrade hydrocarbon compounds was most prevalent in the lower-temperature reservoirs. Sulfate availability, rather than sulfate reduction potential, seems to be the limiting factor for sulfide production in some of the reservoirs under investigation. Most microorganisms in the intermediate- and higher-temperature samples were related to previously studied methanogenic and nonmethanogenic archaea and thermophilic bacteria, but one candidate phylum bacterium, a member of the Acetothermia (OP1), was present in Kuparuk sample K3. The greatest numbers of candidate phyla were recovered from the mesothermic reservoir samples SB1 and SB2. We reconstructed a nearly complete genome for an organism from the candidate phylum Parcubacteria (OD1) that was abundant in sample SB1. Consistent with prior findings for members of this lineage, the OD1 genome is small, and metabolic predictions support an obligately anaerobic, fermentation-based lifestyle. At moderate abundance in samples SB1 and SB2 were members of bacteria from other candidate phyla, including Microgenomates (OP11), Atribacteria (OP9), candidate phyla TA06 and WS6, and Marinimicrobia (SAR406). The results presented here elucidate potential roles of organisms in oil reservoir biological processes.

Potential Activity, Size, and Structure of Sulfate-Reducing Microbial Communities in an Exposed, Grazed and a Sheltered, Non-Grazed Mangrove Stand at the Red Sea Coast.

After oxygen, sulfate is the most important oxidant for the oxidation of organic matter in mangrove forest soils. As sulfate reducers are poor competitors for common electron donors, their relative success depends mostly on the surplus of carbon that is left by aerobic organisms due to oxygen depletion. We therefore hypothesized that sulfate-cycling in mangrove soils is influenced by the size of net primary production, and hence negatively affected by mangrove degradation and exploitation, as well as by carbon-exporting waves. To test this, we compared quantitative and qualitative traits of sulfate-reducing communities in two Saudi-Arabian mangrove stands near Jeddah, where co-occurring differences in camel-grazing pressure and tidal exposure led to a markedly different stand height and hence primary production. Potential sulfate reduction rates measured in anoxic flow-through reactors in the absence and presence of additional carbon sources were significantly higher in the samples from the non-grazed site. Near the surface (0–2 cm depth), numbers of dsrB gene copies and culturable cells also tended to be higher in the non-grazed sites, while these differences were not detected in the sub-surface (4–6 cm depth). It was concluded that sulfate-reducing microbes at the surface were indeed repressed at the low-productive site as could be expected from our hypothesis. At both sites, sulfate reduction rates as well as numbers of the dsrB gene copies and viable cells increased with depth suggesting repression of sulfate reduction near the surface in both irrespective of production level. Additionally, sequence analysis of DNA bands obtained from DGGE gels based on the dsrB gene, showed a clear difference in dominance of sulfate-reducing genera belonging to the Deltaproteobacteria and the Firmicutes between sampling sites and depths.

Passive System for Bio-Recovery of Copper from Acid Mine Drainage

In Central Chile, acid mine drainages (AMDs) are characterized by high concentrations of copper, which can be recovered. Passive biochemical reactors are eco-friendly technologies for the treatment of AMD. They use organic substrate mixtures to drive microbial sulfate reduction and metal sulfide precipitate formation. The performance of conventional biochemical reactors, however, is limited by metal toxicity, and metal recovery is difficult. Diffusive exchange systems on the other hand can be tailored to resist metal toxicity. This is achieved by having separate zones for AMD movement and for sulfate reduction, and by allowing the diffusive exchange of solutes between these zones. Also, higher reaction rates are possible, because much finer organic materials can be utilized as substrates. A key innovation of this research is the use of vertical tubular screens to convey the AMD through the reactor while simultaneously allowing transverse diffusive exchange of dissolved species with the substrate. The tubular screens act as reactors for precipitate formation, settling and accumulation, from where precipitates can be periodically recovered. This design promotes higher reaction rates, eliminates clogging and facilitates the recovery of valuable metals. This work studied the performance of a 2-m long vertical diffusive exchange column. Detailed insight was gained into reactions and transport processes within the tubular screen by the use of several sampling points along the column. During the first two months the reactor was fed with increasing concentrations of sulfate only, to determine its sulfate reduction potential. Then the reactor was fed with AMD for three additional months. During the operation with AMD, significant metal removal occurred, and copper precipitates accumulated, and were recovered.

The impact of acid mine drainage on the methylmercury cycling at the sediment-water interface in Aha Reservoir, Guizhou, China.

The methylmercury (MeHg) cycling at water-sediment interface in an acid mine drainage (AMD)-polluted reservoir (Aha Reservoir) and a reference site (Hongfeng Reservoir) were investigated and compared. Both reservoirs are seasonal anoxic and alkaline. The concentrations of sulfate, sulfide, iron, and manganese in Aha Reservoir were enriched compared to the reference levels in Hongfeng reservoir due to the AMD input. It was found that the MeHg accumulation layer in Aha Reservoir transitioned from the top sediment layer in winter to the water-sediment interface in spring and then to the overlying water above sediment in summer. It supported the assumption that spring methylation activity may start in sediments and migrate into the water column with seasonal variation. The weaker methylation in sediment during spring and summer was caused by the excessive sulfide (∼15-20μM) that reduced the bioavailability of mercury, while sulfate reduction potential was in the optimal range for the methylation in the overlying water. This led to a transport flux of MeHg from water to sediment in spring and summer. In contrast, such inversion of MeHg accumulation layer did not occur in Hongfeng Reservoir. The sulfate reduction potential was in the optimal range for the methylation in top sediment, and dissolved MeHg was positively related to sulfide in pore water of Hongfeng Reservoir (r = 0.67, p < 0.001). This result suggested that accumulation of MeHg in lake water and cycling of MeHg at sediment-water interface associate with some sensitive environmental factors, such as sulfur.

Microbial sulfur transformations in sediments from Subglacial Lake Whillans.

Diverse microbial assemblages inhabit subglacial aquatic environments. While few of these environments have been sampled, data reveal that subglacial organisms gain energy for growth from reduced minerals containing nitrogen, iron, and sulfur. Here we investigate the role of microbially mediated sulfur transformations in sediments from Subglacial Lake Whillans (SLW), Antarctica, by examining key genes involved in dissimilatory sulfur oxidation and reduction. The presence of sulfur transformation genes throughout the top 34 cm of SLW sediments changes with depth. SLW surficial sediments were dominated by genes related to known sulfur-oxidizing chemoautotrophs. Sequences encoding the adenosine-5′-phosphosulfate (APS) reductase gene, involved in both dissimilatory sulfate reduction and sulfur oxidation, were present in all samples and clustered into 16 distinct operational taxonomic units. The majority of APS reductase sequences (74%) clustered with known sulfur oxidizers including those within the “Sideroxydans” and Thiobacillus genera. Reverse-acting dissimilatory sulfite reductase (rDSR) and 16S rRNA gene sequences further support dominance of “Sideroxydans” and Thiobacillus phylotypes in the top 2 cm of SLW sediments. The SLW microbial community has the genetic potential for sulfate reduction which is supported by experimentally measured low rates (1.4 pmol cm-3d-1) of biologically mediated sulfate reduction and the presence of APS reductase and DSR gene sequences related to Desulfobacteraceae and Desulfotomaculum. Our results also infer the presence of sulfur oxidation, which can be a significant energetic pathway for chemosynthetic biosynthesis in SLW sediments. The water in SLW ultimately flows into the Ross Sea where intermediates from subglacial sulfur transformations can influence the flux of solutes to the Southern Ocean.

Effect of sulfate on low-temperature anaerobic digestion.

The effect of sulfate addition on the stability of, and microbial community behavior in, low-temperature anaerobic expanded granular sludge bed-based bioreactors was investigated at 15°C. Efficient bioreactor performance was observed, with chemical oxygen demand (COD) removal efficiencies of >90%, and a mean SO2−4 removal rate of 98.3%. In situ methanogensis appeared unaffected at a COD: SO2−4 influent ratio of 8:1, and subsequently of 3:1, and was impacted marginally only when the COD: SO2−4 ratio was 1:2. Specific methanogenic activity assays indicated a complex set of interactions between sulfate-reducing bacteria (SRB), methanogens and homoacetogenic bacteria. SO2−4 addition resulted in predominantly acetoclastic, rather than hydrogenotrophic, methanogenesis until >600 days of SO2−4-influenced bioreactor operation. Temporal microbial community development was monitored by denaturation gradient gel electrophoresis (DGGE) of 16S rRNA genes. Fluorescence in situ hybridizations (FISH), qPCR and microsensor analysis were combined to investigate the distribution of microbial groups, and particularly SRB and methanogens, along the structure of granular biofilms. qPCR data indicated that sulfidogenic genes were present in methanogenic and sulfidogenic biofilms, indicating the potential for sulfate reduction even in bioreactors not exposed to SO2−4. Although the architecture of methanogenic and sulfidogenic granules was similar, indicating the presence of SRB even in methanogenic systems, FISH with rRNA targets found that the SRB were more abundant in the sulfidogenic biofilms. Methanosaeta species were the predominant, keystone members of the archaeal community, with the complete absence of the Methanosarcina species in the experimental bioreactor by trial conclusion. Microsensor data suggested the ordered distribution of sulfate reduction and sulfide accumulation, even in methanogenic granules.

Microbial habitat connectivity across spatial scales and hydrothermal temperature gradients at Guaymas Basin

The Guaymas Basin (Gulf of California) hydrothermal vent area is known as a dynamic and hydrothermally vented sedimentary system, where the advection and production of a variety of different metabolic substrates support a high microbial diversity and activity in the seafloor. The main objective of our study was to explore the role of temperature and other environmental factors on community diversity, such as the presence of microbial mats and seafloor bathymetry within one hydrothermally vented field of 200 × 250 m dimension. In this field, temperature increased strongly with sediment depth reaching the known limit of life within a few decimeters. Potential sulfate reduction rate as a key community activity parameter was strongly affected by in situ temperature and sediment depth, declining from high rates of 1–5 μmol ml−1 d−1 at the surface to the detection limit below 5 cm sediment depth, despite the presence of sulfate and hydrocarbons. Automated Ribosomal Intergenic Spacer Analysis yielded a high-resolution fingerprint of the dominant members of the bacterial community. Our analyses showed strong temperature and sediment depth effects on bacterial cell abundance and Operational Taxonomic Units (OTUs) number, both declining by more than one order of magnitude below the top 5 cm of the sediment surface. Another fraction of the variation in diversity and community structure was explained by differences in the local bathymetry and spatial position within the vent field. Nevertheless, more than 80% of all detected OTUs were shared among the different temperature realms and sediment depths, after being classified as cold (T < 10°C), medium (10°C ≤ T < 40°C) or hot (T ≥ 40°C) temperature conditions, with significant OTU overlap with the richer surface communities. Overall, this indicates a high connectivity of benthic bacterial habitats in this dynamic and heterogeneous marine ecosystem influenced by strong hydrothermalism.

The impact of sulfate reduction on the distribution of methylmercury in reservoirs in the city of Guiyang

In this paper, the relationship between sulfate reduction potential and mercury methylation potential was studied in the Aha, Baihua and Hongfeng reservoirs from Guiyang City. The methylmercury (MeHg) concentrations of lake water in the Aha Reservoir were greatly elevated as compared to those of the Hongfeng and Baihua reservoirs, which was correlated with its distinctly high SRB abundance, SO42−, and S2− concentrations. Among the three reservoirs, however, the highest MeHg was observed in in the top several centimenters of pore water profile in the Hongfeng Reservoir where the lowest S2− in pore water occurred. The distributions of MeHg in lake water and pore water showed the highest methylation potential occurred at water-sediment surface for the Aha Reservoir and the in the top several centimenters of sediments for the Hongfeng Reservoir. It is guessed that the highest mercury methylation only occurs at the sites with certain sulfide concentrations.

Active sulfur cycling by diverse mesophilic and thermophilic microorganisms in terrestrial mud volcanoes of Azerbaijan

Terrestrial mud volcanoes (TMVs) represent geochemically diverse habitats with varying sulfur sources and yet sulfur cycling in these environments remains largely unexplored. Here we characterized the sulfur-metabolizing microorganisms and activity in four TMVs in Azerbaijan. A combination of geochemical analyses, biological rate measurements and molecular diversity surveys (targeting metabolic genes aprA and dsrA and SSU ribosomal RNA) supported the presence of active sulfur-oxidizing and sulfate-reducing guilds in all four TMVs across a range of physiochemical conditions, with diversity of these guilds being unique to each TMV. The TMVs varied in potential sulfate reduction rates (SRR) by up to four orders of magnitude with highest SRR observed in sediments where in situ sulfate concentrations were highest. Maximum temperatures at which SRR were measured was 60°C in two TMVs. Corresponding with these trends in SRR, members of the potentially thermophilic, spore-forming, Desulfotomaculum were detected in these TMVs by targeted 16S rRNA analysis. Additional sulfate-reducing bacterial lineages included members of the Desulfobacteraceae and Desulfobulbaceae detected by aprA and dsrA analyses and likely contributing to the mesophilic SRR measured. Phylotypes affiliated with sulfide-oxidizing Gamma- and Betaproteobacteria were abundant in aprA libraries from low sulfate TMVs, while the highest sulfate TMV harboured 16S rRNA phylotypes associated with sulfur-oxidizing Epsilonproteobacteria. Altogether, the biogeochemical and microbiological data indicate these unique terrestrial habitats support diverse active sulfur-cycling microorganisms reflecting the in situ geochemical environment.

Metabolically active microbial communities in marine sediment under high-CO2 and low-pH extremes

Sediment-hosting hydrothermal systems in the Okinawa Trough maintain a large amount of liquid, supercritical and hydrate phases of CO(2) in the seabed. The emission of CO(2) may critically impact the geochemical, geophysical and ecological characteristics of the deep-sea sedimentary environment. So far it remains unclear whether microbial communities that have been detected in such high-CO(2) and low-pH habitats are metabolically active, and if so, what the biogeochemical and ecological consequences for the environment are. In this study, RNA-based molecular approaches and radioactive tracer-based respiration rate assays were combined to study the density, diversity and metabolic activity of microbial communities in CO(2)-seep sediment at the Yonaguni Knoll IV hydrothermal field of the southern Okinawa Trough. In general, the number of microbes decreased sharply with increasing sediment depth and CO(2) concentration. Phylogenetic analyses of community structure using reverse-transcribed 16S ribosomal RNA showed that the active microbial community became less diverse with increasing sediment depth and CO(2) concentration, indicating that microbial activity and community structure are sensitive to CO(2) venting. Analyses of RNA-based pyrosequences and catalyzed reporter deposition-fluorescence in situ hybridization data revealed that members of the SEEP-SRB2 group within the Deltaproteobacteria and anaerobic methanotrophic archaea (ANME-2a and -2c) were confined to the top seafloor, and active archaea were not detected in deeper sediments (13-30 cm in depth) characterized by high CO(2). Measurement of the potential sulfate reduction rate at pH conditions of 3-9 with and without methane in the headspace indicated that acidophilic sulfate reduction possibly occurs in the presence of methane, even at very low pH of 3. These results suggest that some members of the anaerobic methanotrophs and sulfate reducers can adapt to the CO(2)-seep sedimentary environment; however, CO(2) and pH in the deep-sea sediment were found to severely impact the activity and structure of the microbial community.

Comparative survey of potential nitrate and sulfate reduction rates in aquatic sediments

Nitrate and sulfate are two major terminal electron acceptors of anaerobic respiration in nearshore sediments. Potential nitrate and sulfate reduction rates (NRR and SRR) were determined on surficial sediments sampled at 14 sites representing a wide range of shallow-water depositional environments. The rates were obtained by supplying undisturbed slices of sediments with nitrate, sulfate or both using a flow-through reactor technique. No external electron donor was added to the sediments. The results indicate that all studied sediments harbored viable and coexisting nitrate- and sulfate-reducing communities, which were able to instantaneously consume the electron acceptors supplied to the reactors. On average, NRR exceeded SRR by about one order of magnitude (309±180nmol NO3- cm−3h−1versus 37±29nmolSO42- cm−3h−1). The NRR:SRR molar ratio, however, varied significantly from site to site, with values ranging from 1.7 to 59. Nitrite production, indicative of incomplete nitrate reduction, was observed in all studied sediments and, on average, accounted for 45% of NRR (range 3–80%). Production of sulfate under nitrate-reducing conditions was observed in 10 out of 14 of the studied sediments, suggesting a common occurrence of sulfide oxidation coupled to nitrate reduction. Oxidation of sulfide accounted for 0 to 40% of NRR in the nitrate-only experiments. When both electron acceptors were supplied simultaneously, net sulfate consumption decreased on average by 45%. The effect of nitrate on SRR was highly variable, however, ranging from near complete inhibition to a 25% enhancement of SRR. Overall, the results of this study point to the need to critically reassess the model formulations used to represent anaerobic respiration processes and their interactions in early diagenetic models.