System performance and microbial community in ethanol-fed anaerobic reactors acclimated with different organic carbon to sulfate ratios

Sulfate influences the organics removal and methanogenic performance during anaerobic wastewater treatment. System performance, microbial community and metabolic pathways in ethanol-fed anaerobic reactors were investigated under different COD/SO₄^2- ratios (2, 1 and 0.67) and control without sulfate addition. The sulfate removal percentages declined (99%, 60% and 49%) with decreasing COD/SO₄^2- ratios, and methanogenesis was completely inhibited. Acetate accumulated to 903-734 mg/L, though propionate was constantly lower than 30 mg/L. Without sulfate, acetate and propionate did not accumulate, despite the extended time for propionate degradation. Incomplete oxidizing sulfate reducing bacteria (Desulfobulbus and Desulfomicrobium) and hydrolysis-acidification genera (Treponema and Bacteroidales) predominated but could not degrade acetate. Desulfobulbus was the key genus for propionate degradation through the pyruvate & propanoate metabolism pathway. Pseudomonas and Desulfobulbus, possessing genes encoding Type IV pili and cytochrome c6 OmcF, respectively, potentially participated in the direct interspecies electron transfer in sulfate-rich conditions.

Isolation, characterization, and genome insights into an anaerobic sulfidogenic Tissierella bacterium from Cu-bearing coins

Recent reports on antimicrobial effects of metallic Cu prompted this study of anaerobic microbial communities on copper surfaces. Widely circulating copper-containing coinage was used as a potential source for microorganisms that had had human contact and were tolerant to copper. This study reports on the isolation, characterization, and genome of an anaerobic sulfidogenic Tissierella sp. P1from copper-containing brass coinage. Dissimilatory (bi)sulfite reductase dsrAB present in strain P1 genome and the visible absorbance around 630 nm in the cells suggested the presence of a desulfoviridin-type protein. However, the sulfate reduction rate measurements with ³⁵SO₄^2- did not confirm the dissimilatory sulfate reduction by the strain. The P1 genome lacks APS reductase, sulfate adenylyltransferase, DsrC, and DsrMK necessary for dissimilatory sulfate reduction. The isolate produced up to 0.79 mM H₂S during growth, possibly due to cysteine synthase (CysK) and/or cysteine desulfhydrase (CdsH) activities, encoded in the genome. The strain can tolerate up to 2.4 mM Cu²⁺(150 mg/l) in liquid medium, shows affinity to metallic copper, and can survive on copper-containing coins up to three days under ambient air and dry conditions. The genome sequence of strain P1 contained cutC, encoding a copper resistance protein, which distinguishes it from all other Tissierella strains with published genomes.

Simultaneous release of polyphosphate and iron-phosphate from waste activated sludge by anaerobic fermentation combined with sulfate reduction

Iron is widely used in sewage treatment systems and enriched into waste activated sludge (WAS), which is difficult and challenging to phosphorus (P) release and recovery. This study investigated simultaneous release performance of polyphosphate and iron-phosphate from iron-rich sludge via anaerobic fermentation combined with sulfate reduction (AF-SR) system. Batch tests were performed, with results showing that AF-SR system conducted a positive effect due to the relatively low solubility of ferrous sulfide in comparison with ferric phosphate precipitates. Simulation study was performed to investigate the total P release potential from actual waste activated sludge, finding that about 70% of the total P could release with the optimized pH of 7.0-8.0 and the theoretical S^2-/Fe²⁺ molar ratio of 1.0. A potential new blueprint of a wastewater treatment plant based on AF-SR system, towards P, N recovery and Fe, S, C recycle, was finally proposed.

Hydrological and hydrochemical behavior of a riparian zone in a high-order flatland stream

Hydrological and hydrochemical processes occurring within riparian zones in temperate mid-latitudes flatland areas have significant implications for water management by controlling nutrient transfer between the watershed and the stream system. The riparian zone in a high-order flatland stream located within a 7063-km² agricultural watershed in Argentina was investigated to study its hydrological connectivity to upland zones, interactions with the stream, and their implications for groundwater hydrochemistry. The analysis was based on 9-year-long time series of groundwater/stream water levels collected along a 220-m-long transect comprising six piezometers, a river stage sensor, and hydrochemical information from 37 groundwater/stream water sampling campaigns. Samples were analyzed for electrical conductivity (EC), Cl^-, SO₄⁺², (Ca⁺² + Mg⁺²), pH, and redox potential (ORP). Data were interpreted using descriptive statistics, statistical tests, groundwater flux calculations, and identification of hydrological patterns and associated hydrochemical responses. The system was hydrologically controlled by shallow groundwater. Three representative landscape hydrological patterns were identified: disconnected, incipient-weakly connected, and fully connected. Groundwater hydrochemistry was closely linked to hydrological connectivity, which played an important role in the mobilization and fluxes of solutes. Overall, groundwater EC, Cl^-, SO₄⁺², and (Ca⁺² + Mg⁺²) concentrations decreased from upland to lowland. For full connectivity, Cl^- concentrations reduced 33%, while SO₄⁺² reduced 42%, demonstrating the system's buffering capacity. This investigation constitutes the first attempt to formulate the riparian zone functioning in this agricultural region and has contributed to the understanding on the complex interactions between hydrologic regimes of large flatland-high-order streams and shallow groundwater systems in fine-texture sediments.

Effect of pressure and temperature on anaerobic methanotrophic activities of a highly enriched ANME-2a community

This study investigated the effect of temperature and methane partial pressure on the anaerobic methane-oxidizing and sulfate-reducing (AOM-SR) activities by a highly enriched ANME-2a community. The ANME-2a-enriched biomass was incubated at different pressures, i.e., 2, 10, 20, and 30 MPa at 15 °C for 80 days. The response of the microbial community with temperature was investigated in incubations at 4, 15, and 25 °C at 10 MPa. Among all tested conditions, the incubation at 10 MPa pressure and 15 °C showed the highest AOM-SR activity of the studied ANME-2a phylotype, whereas activity at 2 MPa pressure and 15 °C was almost comparative to the response at 10 MPa pressure. The finding of the most favorable conditions for AOM-SR activity by the studied AOM-SR community comparable to the in situ pressure and temperature (15 °C at 10 MPa) suggests that the studied ANME-2a phylotype was well adapted to the conditions similar to its origin. The microbial community analysis showed that the bacterial community composition shifted upon changing the incubation temperature and pressure.

A novel aerobic sulfate reduction process in landfill mineralized refuse

It is thought that mineralized refuse could be excavated from almost-full landfill sites to provide space for the increasing burden of municipal solid waste. When excavating, however, the H₂S emissions from the mineralized waste need to be considered carefully. In an attempt to understand how H₂S emissions might change during this excavation process, we carried out a series of tests, including exposing anaerobic mineralized refuse to oxygen, isolating and determining possible functional bacteria, and characterizing the electron donors and/or acceptors. The results showed that H₂S would be released when landfill mineralized refuse was exposed to oxygen (O₂), and could reach concentrations of 6 mg m^-3, which was 3 times the concentrations of H₂S released from anaerobic mineralized refuse. Sulfur-metabolized microorganisms accounted for only 0.5% of the microbial functional bacteria (MFB) derived from the mineralized refuse when exposed to O₂ for 60 days, and SRB were not present. The MFB maintained H₂S production by aerobic sulfate reduction using SO₄^2- and S₂O₃^2- as electron acceptors, and sulfate-reducing rates of 16% and 55%, respectively, were achieved. Lactate and S₂O₃^2- were the preferred electron donor and acceptor, respectively. By enhancing the carbon source and electron transfer, MFB may undergo strong aerobic sulfate reduction even at low abundances of sulfur-metabolized microorganisms.

Enhanced sulfate and metal removal by reduced graphene oxide self-assembled Enterococcus avium sulfate-reducing bacteria particles

Graphene oxide (GO) was introduced to Enterococcus avium strain BY7 sulfate-reducing bacteria culture as a carrier, GO was partially reduced by SRB to reduced graphene oxide (rGO). The rGO could further self-assemble Enterococcus avium strain BY7 sulfate-reducing bacteria to form BY-rGO particles. Growth and sulfate reduction activity of strain BY7 was promoted by rGO, which probably due to the protective effect of rGO, and enhanced electron transfer by rGO as electron shuttle. Effects of pH and temperature variance on strain BY-rGO were remarkably weakened, growth and sulfate reduction were observed from pH 2.0 to 12.0, and from 10 to 45 °C, respectively. Metal toxicity to BY7 strain SRB was sharply decreased in BY-rGO particles and heavy metal removal was remarkably accelerated (up to 50%). The immobilization methods established in this study might open a new way for the application of SRBs, especially under extreme environmental conditions.

The bioenergetics mechanisms and applications of sulfate-reducing bacteria in remediation of pollutants in drainage: A review

Sulfate-reducing bacteria (SRB), a group of anaerobic prokaryotes, can use sulfur species as a terminal electron acceptor for the oxidation of organic compounds. They not only have significant ecological functions, but also play an important role in bioremediation of contaminated sites. Although numerous studies on metabolism and applications of SRB have been conducted, they still remain incompletely understood and even controversial. Fully understanding the metabolism of SRB paves the way for allowing the microorganisms to provide more beneficial services in bioremediation. Here we review progress in bioenergetics mechanisms and application of SRB including: (1) electron acceptors and donors for SRB; (2) pathway for sulfate reduction; (3) electron transfer in sulfate reduction; (4) application of SRB for economical and concomitant treatment of heavy metal, organic contaminants and sulfates. Moreover, current knowledge gaps and further research needs are identified.

Microbial community structure in deep natural gas-bearing aquifers subjected to sulfate-containing fluid injection

In the natural gas field located in central Japan, high concentrations of natural gases and iodide ions are dissolved in formation water and commercially produced in deep aquifers. In the iodine recovery process, the produced formation water is amended with sulfate, and this fluid is injected into gas-bearing aquifers, which may lead to infrastructure corrosion by hydrogen sulfide. In this study, we examined the microbial community in aquifers subjected to sulfate-containing fluid injection. Formation water samples were collected from production wells located at different distances from the injection wells. The chemical analysis showed that the injection fluid contained oxygen, nitrate, nitrite and sulfate, in contrast to the formation water, which had previously been shown to be depleted in these components. Sulfur isotopic analysis indicated that sulfate derived from the injection fluid was present in the sample collected from near the injection wells. Quantitative and sequencing analysis of dissimilatory sulfite reductase and 16S rRNA genes revealed that sulfate-reducing bacteria (SRB), sulfur-oxidizing bacteria, and anaerobic methanotrophic archaea (ANME) in the wells located near injection wells were more abundant than those in wells located far from the injection wells, suggesting that fluid injection stimulated these microorganisms through the addition of oxygen, nitrate, nitrite and sulfate to the methane-rich aquifers. The predominant taxa were assigned to the ANME-2 group, its sulfate-reducing partner SEEP-SRB1 cluster and sulfur-oxidizing Epsilonproteobacteria. These results provide important insights for future studies to support the development of natural gas and iodine resources in Japan.

Viral and metabolic controls on high rates of microbial sulfur and carbon cycling in wetland ecosystems

BACKGROUND

Microorganisms drive high rates of methanogenesis and carbon mineralization in wetland ecosystems. These signals are especially pronounced in the Prairie Pothole Region of North America, the tenth largest wetland ecosystem in the world. Sulfate reduction rates up to 22 μmol cm-3 day-1 have been measured in these wetland sediments, as well as methane fluxes up to 160 mg m-2 h-1-some of the highest emissions ever measured in North American wetlands. While pore waters from PPR wetlands are characterized by high concentrations of sulfur species and dissolved organic carbon, the constraints on microbial activity are poorly understood. Here, we utilized metagenomics to investigate candidate sulfate reducers and methanogens in this ecosystem and identify metabolic and viral controls on microbial activity.

RESULTS

We recovered 162 dsrA and 206 dsrD sequences from 18 sediment metagenomes and reconstructed 24 candidate sulfate reducer genomes assigned to seven phyla. These genomes encoded the potential for utilizing a wide variety of electron donors, such as methanol and other alcohols, methylamines, and glycine betaine. We also identified 37 mcrA sequences spanning five orders and recovered two putative methanogen genomes representing the most abundant taxa-Methanosaeta and Methanoregulaceae. However, given the abundance of Methanofollis-affiliated mcrA sequences, the detection of F420-dependent alcohol dehydrogenases, and millimolar concentrations of ethanol and 2-propanol in sediment pore fluids, we hypothesize that these alcohols may drive a significant fraction of methanogenesis in this ecosystem. Finally, extensive viral novelty was detected, with approximately 80% of viral populations being unclassified at any known taxonomic levels and absent from publicly available databases. Many of these viral populations were predicted to target dominant sulfate reducers and methanogens.

CONCLUSIONS

Our results indicate that diversity is likely key to extremely high rates of methanogenesis and sulfate reduction observed in these wetlands. The inferred genomic diversity and metabolic versatility could result from dynamic environmental conditions, viral infections, and niche differentiation in the heterogeneous sediment matrix. These processes likely play an important role in modulating carbon and sulfur cycling in this ecosystem.

Process integration for biological sulfate reduction in a carbon monoxide fed packed bed reactor

This study examined immobilized anaerobic biomass for sulfate reduction using carbon monoxide (CO) as the sole carbon source under batch and continuous fed conditions. The immobilized bacteria with beads made of 10% polyvinyl alcohol (PVA) showed best results in terms of sulfate reduction (84 ± 3.52%) and CO utilization (98 ± 1.67%). The effect of hydraulic retention time (HRT), sulfate loading rate and CO loading rate on sulfate and CO removal was investigated employing a 1L packed bed bioreactor containing the immobilized biomass. At 48, 24 and 12 h HRT, the sulfate removal was 94.42 ± 0.15%, 89.75 ± 0.47% and 61.08 ± 0.34%, respectively, along with a CO utilization of more than 90%. The analysis of variance (ANOVA) of the results obtained showed that only the initial CO concentration significantly affected the sulfate reduction process. The reactor effluent sulfate concentrations were 27.41 ± 0.44, 59.16 ± 1.08, 315.83 ± 7.33 mg/L for 250, 500 and 1000 mg/L of influent sulfate concentrations respectively, under the optimum operating conditions. The sulfate reduction rates matched well with low inlet sulfate loading rates, indicating stable performance of the bioreactor system. Overall, this study yielded very high sulfate reduction efficiency by the immobilized anaerobic biomass under high CO loading condition using the packed bed reactor system.

Induced bioelectrochemical metabolism for bioremediation of petroleum refinery wastewater: Optimization of applied potential and flow of wastewater

Hybrid based bioelectrochemical system (BES) configured with embedded anode and cathode electrodes in soil was tested for the bioelectrochemical degradation of petroleum refinery wastewater (PRW). Four applied potentials were studied to optimize under batch mode operation, among which 2 V resulted in higher COD degradation (69.2%) and power density (725 mW/m²) during 7 days of operation. Further studies with continuous mode of operation at optimized potential (2 V) showed that hydraulic retention time (HRT) of 19 h achieved the highest COD removal (37%) and highest power density (561 mW/m²). BES function with respect to treatment efficiencies of other pollutants of PRW was also identified with respect to oil and grease (batch mode, 91%; continuous mode, 34%), total dissolved salts (batch mode, 53%; continuous mode, 24%) and sulfates (batch mode, 59%; continuous mode, 42%). Soil microenvironment in association with BES forms complex processes, providing suitable conditions for efficient treatment of PRW.

Enrichment of sulfate reducing anaerobic methane oxidizing community dominated by ANME-1 from Ginsburg Mud Volcano (Gulf of Cadiz) sediment in a biotrickling filter

This study was performed to enrich anaerobic methane-oxidizing archaea (ANME) present in sediment from the Ginsburg Mud Volcano (Gulf of Cadiz) in a polyurethane foam packed biotrickling filter (BTF). The BTF was operated at 20 (±2) °C, ambient pressure with continuous supply of methane for 248 days. Sulfate reduction with simultaneous sulfide production (accumulating ∼7 mM) after 200 days of BTF operation evidenced anaerobic oxidation of methane (AOM) coupled to sulfate reduction. High-throughput sequence analysis of 16S rRNA genes showed that after 248 days of BTF operation, the ANME clades enriched to more than 50% of the archaeal sequences, including ANME-1b (40.3%) and ANME-2 (10.0%). Enrichment of the AOM community was beneficial to Desulfobacteraceae, which increased from 0.2% to 1.8%. Both the inoculum and the BTF enrichment contained large populations of anaerobic sulfur oxidizing bacteria, suggesting extensive sulfur cycling in the BTF.

Data set on the bioprecipitation of sulfate and trivalent arsenic by acidophilic non-traditional sulfur reducing bacteria

Data presented here are related to the original paper "Simultaneous removal of sulfate and arsenic using immobilized non-traditional sulfate reducing bacteria (SRB) mixed culture and alternative low-cost carbon sources" published by same authors (Matos et al., 2018) [1]. The data set here presented aims to facilitate this paper comprehension by giving readers some additional information. Data set includes a brief description of experimental conditions and the results obtained during both batch and semi-continuous reactors experiments. Data confirmed arsenic and sulfate were simultaneously removed under acidic pH by using a biological treatment based on the activity of a non-traditional sulfur reducing bacteria consortium. This microbial consortium was able to utilize glycerol, powdered chicken feathers as carbon donors, and proved to be resistant to arsenite up to 8.0 mg L^-1. Data related to sulfate and arsenic removal efficiencies, residual arsenite and sulfate contents, pH and Eh measurements obtained under different experimental conditions were depicted in graphical format. Refers to https://doi.org/10.1016/j.cej.2017.11.035.

Sulfate reduction processes in salt marshes affected by phosphogypsum: Geochemical influences on contaminant mobility

Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, which suggest partial sulfide oxidation, but marsh may have capacity to buffer potential release of contaminants. The importance of sulfur species was quantitatively confirmed by XANES, which also supports the accuracy of selective extraction schemes. Accordingly, managing pore-water quality through organic carbon-rich amendments over phosphogypsum stacks could lead to a decrease in contaminant loading of leakages resulting from weathering.

Characterization of trace metal removal products in vertical flow bioreactor substrates at the Mayer Ranch Passive Treatment System in the Tar Creek Superfund Site

A passive treatment system (PTS), including two parallel vertical flow bioreactors (VFBR), was constructed in 2008 for the treatment of unabated net-alkaline ferruginous mine drainage in the Tar Creek Superfund Site in northeastern Oklahoma. Water quality data collected since the PTS began operation indicate significant removal of trace metals in the VFBR. Results of a sequential extraction procedure (SEP) performed on substrate samples showed that the majority of Cd, Co, Fe, Ni, Pb, and Zn were retained in the refractory organic/sulfide fraction. Subsequent acid volatile sulfide/simultaneously extracted metals (AVS/SEM) analyses confirmed the retention of Cd, Fe, Pb, and Zn as sulfides, but Co and Ni results were less certain. The majority of trace metals were retained as insoluble products in the VFBR, while up to 20% of most of the trace metals were retained in soluble, bioavailable fractions. Nearly 70% of Mn was retained in the soluble and bioavailable exchangeable, carbonate, and labile organic fractions.

Methanogenic and Sulfate-Reducing Activities in a Hypersaline Microbial Mat and Associated Microbial Diversity

Methanogenesis and sulfate reduction are important microbial processes in hypersaline environments. However, key aspects determining substrate competition between these microbial processes have not been well documented. We evaluated competitive and non-competitive substrates for stimulation of both processes through microcosm experiments of hypersaline microbial mat samples from Guerrero Negro, Baja California Sur, Mexico, and we assessed the effect of these substrates on the microbial community composition. Methylotrophic methanogenesis evidenced by sequences belonging to methanogens of the family Methanosarcinaceae was found as the dominant methanogenic pathway in the studied hypersaline microbial mat. Nevertheless, our results showed that incubations supplemented with acetate and lactate, performed in absence of sulfate, also produced methane after 40 days of incubation, apparently driven by hydrogenotrophic methanogens affiliated to the family Methanomicrobiaceae. Sulfate reduction was mainly stimulated by addition of acetate and lactate; however, after 40 days of incubation, an increase of the H₂S concentrations in microcosms amended with trimethylamine and methanol was also observed, suggesting that these substrates are putatively used for sulfate reduction. Moreover, 16S rRNA gene sequencing analysis showed remarkable differences in the microbial community composition among experimental treatments. In the analyzed sample amended with acetate, sulfate-reducing bacteria (SRB) belonging to the family Desulfobacteraceae were dominant, while members of Desulfohalobiaceae, Desulfomicrobiaceae, and Desulfovibrionaceae were found in the incubation with lactate. Additionally, we detected an unexpected high abundance of unclassified Hydrogenedentes (near 25%) in almost all the experimental treatments. This study contributes to better understand methanogenic and sulfate-reducing activities, which play an important role in the functioning of hypersaline environments.

Response of morphology and microbial community structure of granules to influent COD/SO42 - ratios in an upflow anaerobic sludge blanket (UASB) reactor treating starch wastewater

Biochemical properties of granules are of vital importance to UASB performance. This study characterized the granules cultivated at different COD/SO₄^2- ratios to elucidate the influence of sulfidogenesis on starch wastewater (1000 mg-COD L^-1) biodegradation kinetics and process stability. Suitable sulfate addition enriched granular microecosystems and stimulated the secretion of extracellular substances, facilitating cells cohersion and sludge aggregation. The percentage of granules larger than 2.8 mm increased from <10.0% to 58.8-69.4% with decreasing COD/SO₄^2- ratio from 10 to 2. Starch-fed granules tended to grow flagella-like filaments on the surface. The filaments overwhelmed by hydrophilic biopolymers had high affinity for biogas-bubbles and water-molecules aggravating granule floatation and washout. 16 s rRNA gene analysis revealed that decreasing COD/SO₄^2- ratio shifted Syntrophobacterales to Desulfovibrio, which co-worked with Methanosaeta while suppressing Methanobacterium thereby altering starch bioconversion routes. Decrease in Syntrophobacterales caused propionate accumulation and slight process upset.

Methylmercury complexes: Selection of thermodynamic properties and application to the modelling of a column experiment

Complexation with methyl groups produces the most toxic form of mercury, especially because of its capacity to bioconcentrate in living tissues. Understanding and integrating methylation and demethylation processes is of the utmost interest in providing geochemical models relevant for environmental assessment. In a first step, we investigated methylation at equilibrium, by selecting the thermodynamic properties of different complexes that form in the chemical system Hg-SO₃-S-Cl-C-H₂O. The selection included temperature dependencies of the equilibrium constants when available. We also considered adsorption and desorption reactions of both methylated and non-methylated mercury onto mineral surfaces. Then we assessed the kinetics of methylation by comparing a dedicated column experiment with the results of a geochemical model, including testing different methylation and demethylation kinetic rate laws. The column system was a simple medium: silicic sand and iron hydroxides spiked with a mercury nitrate solution. The modelling of methylmercury production with two different rate laws from the literature is bracketing the experimental results. Dissolved mercury, iron and sulfate concentrations were also correctly reproduced. The internal evolution of the column was also correctly modeled, including the precipitation of mackinawite (FeS) and the evolution of dissolved iron. The results validate the conceptual model and underline the capacity of geochemical models to reproduce some processes driven by bacterial activity.

Effect of microbially mediated iron mineral transformation on temporal variation of arsenic in the Pleistocene aquifers of the central Yangtze River basin

Significant seasonal variation of groundwater arsenic (As) concentrations in shallow aquifers of the Jianghan Plain, central Yangtze River Basin has been reported recently, but the underlying mechanisms remain not well understood. To elaborate biogeochemical processes responsible for the observed As concentration variation, 42-day incubation experiments were done using sediment samples collected respectively from the depth of 26, 36 and 60m of the As-affected aquifer which were labeled respectively as JH26, JH36, JH60. Where JH denotes Jianghan Plain, and the number indicates the depth of the sediment sample. The results indicated that As could be mobilized from the sediments of 26m and 36m depth under the stimulation of exogenous organic carbon, with the maximum As release amount of 1.60 and 1.03mgkg^-1, respectively, while the sediments at 60m depth did not show As mobilization. The microbially mediated reductive dissolution of amorphous iron oxides and reduction of As(V) to As(III) could account for the observed As mobilization. The 16S rRNA high-throughput sequencing results indicated that the variation of microbial community correlated with the released As concentration (R=0.7, P<0.05) and the iron-reducing bacteria, including Pseudomonas, Clostridium and Geobacter, were the main drivers for the As mobilization from the sediments at 26m and 36m depth. The increase of arsC gene abundance (up to 1.4×10⁵ copies g^-1) during As release suggested that As reduction was mediated by the resistant reduction mechanism. By contrast, in the 60m sediments where the Fe and As release was absent, the iron-reducing bacteria accounted for a very minor proportion and sulfate-reducing bacteria were predominant in the microbial community. In addition, after 30days of incubation, the released As in the 26m sediments was immobilized via co-precipitation with or adsorption onto the Fe-sulfide mineral newly-formed by the bacterial sulfate reduction. These results are consistent with the results of our previous field monitoring, indicating that the bacterial sulfate reduction could lead to the temporal decrease in groundwater As concentrations. This study provides insights into the mechanism for As mobilization and seasonal As concentration variation in the Pleistocene aquifers from alluvial plains.

Nitrate attenuation in low-permeability sediments based on isotopic and microbial analyses

This study investigated nitrate attenuation in low-permeability sediments (LPS) in a multi-layer aquifer by integrating hydrochemical, isotopic and microbiological molecular techniques in a field site. In the meantime, the overlying high-permeability sediment (HPS) was also examined on the nitrate attenuation for the sake of comparison. Additionally, laboratory flow-through experiments were conducted to assess the overall nitrate reduction rate in the two types of sediment. The δ¹⁵N-NO₃^- and δ³⁴S-SO₄^2- values were more enriched by approximately 37‰ and 15‰ in the LPS than the overlying HPS associated with substantial reductions of the NO₃^- and SO₄^2- concentration, indicating the occurrence of strong bio-reductions in nitrate and sulfate. The microbial community diversity analyses showed a higher diversity of the denitrifiers encoding nirS- (Shannon Index SI=6.3) and nrf-type gene (SI=2.7), and the sulfate reduction bacteria (SRB) encoding the dsr gene (SI=6.4) in the LPS than in the HPS. The bacterial community structure was influenced by the groundwater hydrochemistry and the redox conditions. Due to the presence of anoxic groundwater with low levels of nutrients, the LPS featured higher abundances of nitrate reducers belonging to Alphaproteobacteria and SRB belonging to the strictly anaerobic class Clostridia relative to the HPS. Notably, chemolithotrophs were abundant in the LPS and likely coupled the reduction of nitrate with the oxidation of iron. Furthermore, the LPS was demonstrated to attenuate nitrate at a rate two times of the HPS in flow-through experiments, and denitrification accounted for approximately 93% of the nitrate reduction. The high nitrate reduction rate of the LPS was likely attributable to its high functional genes diversity. This study confirmed the occurrence of strong nitrate attenuation in the LPS. The LPS was found to play a significant role in protecting aquifers from anthropogenic contamination.

Modelling sulfate reduction in anaerobic digestion: Complexity evaluation and parameter calibration

A comparative analysis of five different structures of sulfate reduction (SR) models for anaerobic digestion (AD) was conducted to evaluate their accuracy to provide model developers and users with better information to decide on the optimum degree of complexity. The models evaluated differ in terms of the number/type of sulfate reducing bacterial activities considered based on the electron donors used. A systematic calibration of the evaluated models against a large set of experimental data was also conducted using a very recent parameter calibration method. Results indicate that a simple model incorporating both acetate utilizing and hydrogen utilizing sulfate reducing bacterial activities (the M_AH model) achieves a good balance between performance and complexity in terms of prediction errors against experimental data. All the models evaluated provided acceptable predictions except the model including only hydrogen utilizing sulfate reducing bacterial activity. More complex model structures are recommended only if required in specific experimental cases.

Are acid volatile sulfides (AVS) important trace metals sinks in semi-arid mangroves?

Acid-volatile sulfides (AVS) formation and its role on trace metals bioavailability were studied in semi-arid mangroves. The semi-arid climatic conditions at the studied sites, marked by low rainfall and high evapotranspiration rates, clearly limited the AVS formation (AVS contents varied from 0.10 to 2.34μmolg^-1) by favoring oxic conditions (Eh>+350mV). The AVS contents were strongly correlated with reactive iron and organic carbon (r=0.84; r=0.83 respectively), evidencing their dominant role for AVS formation under semi-arid conditions. On the other hand, the recorded ΣSEM/AVS values remained >1 evidencing a little control of AVS over the bioavailability of trace metals and, thus, its minor role as a sink for toxic metals.

Complete genome sequence analysis of Archaeoglobus fulgidus strain 7324 (DSM 8774), a hyperthermophilic archaeal sulfate reducer from a North Sea oil field

Archaeoglobus fulgidus is the type species of genus Archaeoglobus Stetter 1998, a hyperthermophilic sulfate reducing group within the Archaeoglobi class of the euryarchaeota phylum. Members of this genus grow heterotrophically or chemolithoautotrophically with sulfate or thiosulfate as electron acceptors. Except for A. fulgidus strain 7324 and the candidate species “Archaeoglobus lithotrophicus”, which both originate from deep oil-fields, the other members of this genus have been recovered from marine hydrothermal systems. Here we describe the features of the A. fulgidus strain 7324 genome as compared to the A. fulgidus VC16 type strain. The 2.3 Mbp genome sequence of strain 7324 shares about 93.5% sequence identity with that of strain VC16^T but is about 138 Kbp longer, which is mostly due to two large ‘insertions’ carrying one extra cdc6 (cell-cycle control protein 6) gene, extra CRISPR elements and mobile genetic elements, a high-GC ncRNA gene (hgcC) and a large number of hypothetical gene functions. A comparison with four other Archaeoglobus spp. genomes identified 1001 core Archaeoglobus genes and more than 2900 pan-genome orthologous genes.

Bridging spatially segregated redox zones with a microbial electrochemical snorkel triggers biogeochemical cycles in oil-contaminated River Tyne (UK) sediments

Marine sediments represent an important sink for a number of anthropogenic organic contaminants, including petroleum hydrocarbons following an accidental oil spill. Degradation of these compounds largely depends on the activity of sedimentary microbial communities linked to biogeochemical cycles, in which abundant elements such as iron and sulfur are shuttled between their oxidized and reduced forms. Here we show that introduction of a small electrically conductive graphite rod ("the electrochemical snorkel") into an oil-contaminated River Tyne (UK) sediment, so as to create an electrochemical connection between the anoxic contaminated sediment and the oxygenated overlying water, has a large impact on the rate of metabolic reactions taking place in the bulk sediment. The electrochemical snorkel accelerated sulfate reduction processes driven by organic contaminant oxidation and suppressed competitive methane-producing reactions. The application of a comprehensive suite of chemical, spectroscopic, biomolecular and thermodynamic analyses suggested that the snorkel served as a scavenger of toxic sulfide via a redox interaction with the iron cycle. Taken as a whole, the results of this work highlight a new strategy for controlling biological processes, such as bioremediation, through the manipulation of the electron flows in contaminated sediments.