High Sulfate Reduction Research Articles

Analyses of spatial distributions of sulfate-reducing bacteria and their activity in aerobic wastewater biofilms.

The vertical distribution of sulfate-reducing bacteria (SRB) in aerobic wastewater biofilms grown on rotating disk reactors was investigated by fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. To correlate the vertical distribution of SRB populations with their activity, the microprofiles of O(2), H(2)S, NO(2)(-), NO(3)(-), NH(4)(+), and pH were measured with microelectrodes. In addition, a cross-evaluation of the FISH and microelectrode analyses was performed by comparing them with culture-based approaches and biogeochemical measurements. In situ hybridization revealed that a relatively high abundance of the probe SRB385-stained cells (approximately 10(9) to 10(10) cells per cm(3) of biofilm) were evenly distributed throughout the biofilm, even in the oxic surface. The probe SRB660-stained Desulfobulbus spp. were found to be numerically important members of SRB populations (approximately 10(8) to 10(9) cells per cm(3)). The result of microelectrode measurements showed that a high sulfate-reducing activity was found in a narrow anaerobic zone located about 150 to 300 microm below the biofilm surface and above which an intensive sulfide oxidation zone was found. The biogeochemical measurements showed that elemental sulfur (S(0)) was an important intermediate of the sulfide reoxidation in such thin wastewater biofilms (approximately 1,500 microm), which accounted for about 75% of the total S pool in the biofilm. The contribution of an internal Fe-sulfur cycle to the overall sulfur cycle in aerobic wastewater biofilms was insignificant (less than 1%) due to the relatively high sulfate reduction rate.

Contribution of hydrogen to methane production and control of hydrogen concentrations in methanogenic soils and sediments

Hydrogen is, with acetate, one of the most important intermediates in the methanogenic degradation of organic matter and serves as substrate for methanogenic archaea. Hydrogen should theoretically account for 33% of total methanogenesis when carbohydrates or similar forms of organic matter are degraded. Many methanogenic environments show both much lower and much higher contributions of H2 to CH4 production than is considered normal. While the lower contributions are relatively easily explained (e.g. by the contribution of homoacetogenesis), the mechanisms behind higher contributions are mostly unclear. In methanogenic environments H2 is rapidly turned over, its concentration being the result of simultaneous production by fermenting plus syntrophic bacteria and consumption by methanogenic archaea. The steady-state concentration observed in most methanogenic environments is close to the thermodynamic equilibrium of H2-dependent methanogenesis. The threshold is usually equivalent to a Gibbs free energy of −23 kJ mol−1 CH4 that is necessary to couple CH4 production to the generation of 1/3 ATP. Methanogenesis from H2 is inhibited if the H2 concentration decreases below this threshold. Concentrations of H2 can only be decreased below this threshold if a H2-consuming reaction with a lower H2 threshold (e.g. sulfate reduction) takes over at a rate that is equal to or higher than that of methanogenesis. The instantaneous and complete inhibition of H2-dependent CH4 production that is often observed upon addition of sulfate can only be explained if a comparably high sulfate reduction potential is cryptically present in the methanogenic environment.

Methane production and emission from peat: the influence of anions (sulphate, nitrate) from acid rain

The influence of sulphate concentrations on the production and emission of methane in two contrasting peat sites was determined. Seasonal changes in sulphate concentrations appeared to influence the amount of organic carbon oxidised to carbon dioxide by sulphate reduction at both peat sites. For the majority of the year at both sites the amount of carbon mineralised through sulphate reduction exceeded that being transformed to methane by methanogenic bacteria, except when sulphate reduction became sulphate limited. In order to sustain the high sulphate reduction rates measured in the peat sulphide formed from dissimilatory sulphate reduction must be reoxidised rapidly to sulphate within the peat. Laboratory experiments showed that addition of 500 μM sulphate and 100 μM nitrate to peat samples significantly inhibited methanogenesis. Sulphate appeared to be the more important inhibitor of methanogenesis since inhibition of methane formation occurred with additions of sulphate reflecting in situ concentrations. Supplements of either acetate and/or hydrogen in combination with molybdate to peat samples revealed that methanogenesis was hydrogen limited and that the majority of active methanogens were hydrogen-utilising methanogens. Methanogenesis in peat samples appeared to be dependant on sulphate reducing bacteria for provision of substrates. Great Dun Fell, receiving the largest sulphate loading, had the lower rates of microbial activity (methane formation and sulphate reduction rates) than Ellergower, which received less than half the annual sulphate deposition of Great Dun Fell. This implied that some other factor—possibly organic matter lability, was limiting microbial rates of methane formation and sulphate reduction at Great Dun Fell.

Microbial Abundance and Activity in a Low-Conductivity Aquifer System in East-Central Texas

aquifer sands (28‐31 m), even though the total organic carbon content was very low. Rates of anaerobic H2, lactate, and formate consumption were also high in aquifer sands, relative to the other strata. The higher microorganism numbers and activities in the aquifer sediments likely reflect the importance of increased electron donor and acceptor transport in higher hydraulic conductivity sands, relative to other strata. The presence of sulfate and near absence of other electron acceptors (O2 ,N O 3 , and Fe 3+ ), absence of methanogens, high numbers of SRB, and relatively high sulfate reduction activity suggest that sulfate reduction is the dominant terminal electron-accepting process in the deep aquifer. In contrast to aerobic Atlantic Coastal Plain sediments, aquifer sediments at 30 m in this east-central Texas aquifer contain greater numbers of anaerobes than aerobes. Low pH and high sulfate contents argue for oxidation of pyrite in or near the shallow aquifer. This pyrite oxidation supplies sulfate to deeper aquifers. Pyrite from the deep aquifer sediments, with the greatest abundance and activity of SRB, is too enriched in 34 S (up to 58‰) to have formed from modern or typical groundwater sulfate. Overall, our results suggest that the resident microbiota are capable of cycling carbon and sulfur in the aquifer, but probably without substantial remineralization of pyrite in the formation.

Dissimilatory sulfate reduction and methane production in Gotland Deep sediments (Baltic Sea) during a transition period from oxic to anoxic bottom water (1993-1996)

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 14:183-193 (1998) - doi:10.3354/ame014183 Dissimilatory sulfate reduction and methane production in Gotland Deep sediments (Baltic Sea) during a transition period from oxic to anoxic bottom water (1993-1996) Levent Piker*, Rolf Schmaljohann, Johannes F. Imhoff** Institut für Meereskunde, Abteilung für Marine Mikrobiologie, Düsternbrooker Weg 20, D-24105 Kiel, Germany *Present address: Coastal Research and Management, Zum Tamberg 2, D-24247 Mielkendorf, Germany **Addressee for correspondence. E-mail: jimhoff@ifm.uni-kiel.de During a transition period from oxic to anoxic conditions in the bottom water, rates of sulfate reduction and methane production, methane fluxes, as well as concentration profiles of sulfate, sulfide and methane were measured in sediments at a central site of the Gotland Deep (Stn AL 93, 241 m depth), which is regarded as representative for the deepest part of this basin. During this period from 1993 to 1996 oxic conditions in the bottom water prevailed from spring 1994 until summer 1995 with oxygen concentrations decreasing progressively with time. In the sediments methane production occurred primarily in layers below 1 m depth and flux rates of methane to the sediment surface were characterized by a steep concentration gradient from approx. 5 mM at 4 m depth to values close to 30 μM at the surface, determined by diffusion processes and anaerobic oxidation of methane. Both processes were independent of changes at the sediment surface. Differences in the flux rates of methane between the deeper part with a mean value of 259 μmol m-2 d-1 and the upper layers with a mean of 47.7 μmol m-2 d-1 indicate that a considerable proportion of the methane is oxidized within the anoxic horizon of the sediment (71 to 86% in the layer from 40 to 70 cm). Low rates of methane production found within the top 20 cm of the sediment during periods of oxic bottom water increased after depletion of oxygen and resulted in a clear maximum of the methane concentration in the top 2 cm. Sulfate concentrations declined exponentially from values of 11.5 mM in June 1994 and 8.5 mM in October 1995 at the sediment surface to values of 2.5 mM at 20 cm depth and of less than 0.5 mM at 50 to 60 cm depth. High sulfate reduction rates (150 to 250 nmol cm-3 d-1) in the upper part of the sediment (8 to 13 cm) coincided with maxima of sulfide concentrations. During the time period of this investigation an increase of maximum sulfide concentrations in the sediment from 1 to 10 mM was measured together with decreasing oxygen concentrations in the deep water. At the same time sulfate reduction established a small but distinct maximum at the top layer of the sediment (0 to 2 cm). The relative importance of sulfate reduction and methanogenesis in the carbon budget of the Gotland Deep sediments is calculated on the basis of the actual measurements. Sulfate reduction · Sulfide · Methane production · Methane fluxes · Gotland Deep · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 14, No. 2. Publication date: February 13, 1998 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1998 Inter-Research.

Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments

Isotope fractionation during sulfate reduction by natural populations of sulfate-reducing bacteria was investigated in the cyanobacterial microbial mats of Solar Lake, Sinai and the sediments of Løgten Lagoon sulfuretum, Denmark. Fractionation was measured at different sediment depths, sulfate concentrations, and incubation temperatures. Rates of sulfate reduction varied between 0.1 and 37 μmol cm −3d −1, with the highest rates among the highest ever reported from natural sediments. The depletion of 34S during dissimilatory sulfate reduction ranged from 16%. to 42%., with the largest 34S-depletions associated with the lowest rates of sulfate reduction and the lowest 34S-depletions with the highest rates. However, at high sulfate reduction rates (>10 μmol cm −3d −1)the lowest fractionation was 20%. independent of the rates. Overall, there was a similarity between the fractionation obtained by the natural populations of sulfate reducers and previous measurements from pure cultures. This was somewhat surprising given the extremely high rates of sulfate reduction in the experiments. Our results are explained if we conclude that the fractionation was mainly controlled by the specific rate of sulfate reduction (mass cell −1 time −1) and not by the absolute rate (mass volume −1 time −1).Sedimentary sulfides (mainly FeS 2) were on average 40%. depleted in 34S compared to seawater sulfate. This amount of depletion was more than could be explained by the isotopic fractionations that we measured during bacterial sulfate reduction. Therefore, additional processes contributing to the fractionation of sulfur isotopes in the sediments are indicated. From both Solar Lake and Løgten Lagoon we were able to enrich cultures of elemental sulfur-disproportionating bacteria. We suggest that isotope fractionation accompanying elemental sulfur disproportionation contributes to the 34S depletion of sedimentary sulfides at our study sites.

Sulfate reduction and methanogenesis in a Thioploca-dominated sediment off the coast of Chile

Continental shelf sediments of the central Chile upwelling area are dominated by the presence of dense mats of the filamentous, sulfur-depositing bacterium Thioploca spp. We examined rates and pathways of S and methane cycling in these sediments along a transect from the Bay of Concepción to the continental slope. Sulfate reduction rates (170–4670 nmol cm −3 d −1) were equal to or exceeded rates reported for other subtidal marine sediments. Elemental S and pyrite were the dominant end-products of sulfate reduction in Thioploca mats on the continental shelf, whereas, in the highly-reducing, Beggiatoa-dominated sediments of the nearby Bay of Concepción, acid-volatile S was the principal end-product. Dissolved organic C values were lowest at the stations with the highest sulfate reduction rates and increased offshore. Sediment porewater methane concentrations in all surface sediments were low (<12 nmol cm −3), and methane production rates at the station most dominated by Thioploca were extremely low ( <0.5 nmol cm −3 d −1). Low methane production rates and concentrations were matched by low methane oxidation rates (<0.1 nmol cm −3 d −1). Radio-tracer studies showed that methane production was almost exclusively from methylamines, substrates which are noncompetitive with sulfate reduction, rather than from acetate or CO 2/H 2. Bacterial MPN (most probable number) counts also indicated the presence of a methylotrophic population of methanogens. Surprisingly, high numbers of autotrophic acetogenic bacteria were found, suggesting that the bacterial population involved in anaerobic DOC degradation is more complex than expected. In spite of the high sulfate reduction rates, sulfide concentrations in the shelf and slope were low or undetectable (<0.5 μM), and sulfate concentrations were never depleted below bottom water levels down to depths of 25–30 cm. Calculations suggest that Thioploca were oxidizing a maximum of 35% of sulfide production—not enough to prevent sulfate depletion. Either other sulfide oxidizers were also present or transient hydrodynamic conditions coupled with bioturbation resulted in oxidation of the sediments.

Effect of sulfate on anaerobic processes fed with dual substrates

Anaerobic reactors were operated in a semi-batch mode and fed with the dual substrates glucose (G) plus acetic acid (Ac) as primary organic sources to study the effect of sulfate on COD oxidation. With glucose, COD removal by methane formation was seriously inhibited, resulting in COD accumulation in the reactor. Although acetic acid can be consumed by some sulfate-reducing species, it was not a major substrate for sulfate reduction, but was largely responsible for methane formation in the anaerobic mixed culture used in this study. With dual substrates, extreme inhibition of methanogenesis did not occur as did with glucose alone. Instead, methanogens were found to work in harmony with acid formers as well as sulfate reducers to oxidise COD. Interestingly, from 12-hour monitoring, increased G/Ac COD ratios decreased COD removal rates as well as biogas production, but resulted in higher sulfate reduction. This suggests that there should be an optimal feed G/Ac COD ratio, for which removal of both organics could be maximised.

Sulfate reducing and methane producing bacteria in aerobic wastewater treatment systems

A selection of aerobic biofilm reactors and activated sludge plants were investigated for the presence of methane producing bacteria (MPB) and sulfate reducing bacteria (SRB). Detection tests showed that acetotrophic and hydrogenotrophic MPB as well as lactate, acetate and propionate oxidizing SRB were present in all reactor types investigated, except in an activated sludge reactor aerated with pure oxygen. Methane production rates from acetate by biomass samples of aerobic reactors were less than 1% of the rates measured in anaerobic UASB sludge. The presence of SRB was independent of the reactor configuration, the organic loading and the influent sulfate concentration. Aerobic biofilms growing in a trickling filter packed with plastic carrier and in a rotating biological contactor contained between 5.7 × 10 7 to 1.1 × 10 8 CFU/g VS of lactate oxidizing SRB and showed a potential sulfate reduction rate using lactate as electron donor of about 10 mg SO 2− 4/g VS·h. The latter is comparable to the values found in sludges from typical anaerobic wastewater treatment reactors. In activated sludges, SRB densities were some 10 3 time lower and the maximum sulfate reduction rate was ca 3 times lower compared to the aerobic biofilm reactors. In biofilms, high sulfate reduction rates, in combination with the high sulfide removal rates (11.6 to 131.7 mg HS −/g VS·h) suggest that in situ reoxidation of sulfide might sustain the SRB population. The SRB enumeration, together with activity and oxygen microprofile measurements showed that the biomass of aerobic wastewater treatment systems can serve as inoculum or as site for a wide spectrum of redox related biotransformation processes.

Effect of sulfate on anaerobic processes fed with dual substrates

Anaerobic reactors were operated in a semi-batch mode and fed with the dual substrates glucose (G) plus acetic acid (Ac) as primary organic sources to study the effect of sulfate on COD oxidation. With glucose, COD removal by methane formation was seriously inhibited, resulting in COD accumulation in the reactor. Although acetic acid can be consumed by some sulfate-reducing species, it was not a major substrate for sulfate reduction, but was largely responsible for methane formation in the anaerobic mixed culture used in this study. With dual substrates, extreme inhibition of methanogenesis did not occur as did with glucose alone. Instead, methanogens were found to work in harmony with acid formers as well as sulfate reducers to oxidise COD. Interestingly, from 12-hour monitoring, increased G/Ac COD ratios decreased COD removal rates as well as biogas production, but resulted in higher sulfate reduction. This suggests that there should be an optimal feed G/Ac COD ratio, for which removal of both organics could be maximised.

The carbon-sulfide-iron relationship and sulfate reduction rate in the East China Sea continental shelf sediments.

Carbon/sulfide/iron relationship and sulfate reduction rate were investigated in the East China Sea continental shelf sediments. The area is characterized by median to high sulfate reduction rate, and high concentrations of iron oxide minerals. Organic carbon was found to be the primary limiting factor for the pyrite formation. Sulfate reduction rate increased with increasing organic carbon concentration. C/S ratio displays a typical normal marine sediment ratio. Low DOP values and abundance of highly reactive iron oxide, ferrihydrite and lepidocrocite, indicate that iron is not limited in the East China Sea continental shelf.

Enhancement of accumulation and anoxic degradation of organic matter controlled by cyclic productivity: a model

The aim of the study is to determine the relative influences of the genetic sources, the export efficiency, and the anaerobic degradation of organic carbon as factors controlling short-term cyclic organic-rich sedimentation in areas of high marine productivity. A cyclic organic sequence of the Kimmeridge Clay Formation of Yorkshire (U.K) was studied as an example of ancient sedimentation. This formation outcropping in the Cleveland basin near Marton is known as a lateral equivalent of the major oil source rock unit of the North Sea. On the basis of petrographic and geochemical results, a new model is proposed to explain the short-term cyclic sedimentation of organic carbon under continuously anoxic bottom conditions. The model assumes that the cyclicity is primarily controlled by variations of mineral-free phytoplanktonic productivity. Such variations are thought to induce changes in carbon recycling in the photic zone so that the export efficiency of the metabolizable organic matter is modified. A high sulphate reduction intensity relative to the organic matter flux is observed for the highest productivity periods, which also reflects an enhancement of export efficiency. As the redox conditions did not change significantly, such variations in sulphate reduction intensity must be attributed not only to quantitative variations in the export productivity, but also to its qualitative variations, with more metabolizable organic matter reaching the anoxic domain during high productivity periods. Biosedimentary processes depending on productivity, such as aggregation, are thought to play an important role in reducing the transit time of metabolizable organic matter to the sediment. Finally, the model implies that the amplitude of export productivity variations probably were larger than that of TOC variations recorded in sediment which are mainly due to biologically refractory organic matter from plankton.

Geochemistry of mercury in an intertidal flat of the Scheldt estuary

Sediments were sampled on the ‘Groot Buitenschoor’, an intertidal flat located at about 60 km from the Scheldt's river mouth. Hg concentrations ranged from 30 to 1756 ng g−1. The concentrations were strongly correlated with fine grain fraction, organic matter content and sulphide concentrations. Incubation experiments were performed in order to determine the potential methylation rate of Hg as well as biotic and abiotic factors influencing this transformation. About 1 to 2% of the added inorganic Hg is converted into methylmercury. This conversion rate points to the same equilibrium ratio as was observed in natural sediments, indicating an equilibrium between methylation and demethylation reactions in the sediments. Incubation of a sterilised sediment sample significantly decreased the methylation rate, but the methylmercury concentrations observed are still ten times higher than the natural (unspiked) sediment. This result could be due to a chemical (non-enzymatic) methylation of mercury. Sulphate reducing bacteria are the main species responsible for the methylation of Hg at this site. Addition of Na2MoO4, a specific inhibitor of sulphate reducing bacteria, decreased the methylation rate to the abiotic level (sterilised sediment). High sulphate reduction rates, however, lead to lower methylation rates. Increased formation of sulphides due to microbial sulphate reduction leads to enhanced HgS formation and this reaction competes with the methylation process. HgS is in fact the major product formed by the reaction of sulphate reducing bacteria with Hg species. About 50% of the Hg spiked to the sediments is transformed into HgS during the incubation experiments, and that compound is practically unavailable for methylation in contrast to other bound forms of Hg.

Impaired hydrogen metabolism in pneumatosis cystoides intestinalis

Background: Pneumatosis cystoides intestinalis (PCI) is characterized by high levels of breath hydrogen. Clinical features of PCI may be due to abnormal H2 metabolism. Methods: Breath levels of H2 and CH4 were measured in 3 patients and total gas in 2 patients with PCI on a polysaccharide-free (basal) diet and after administration of 15 g of lactulose. Metabolic activities and counts of methanogenic (MB) and sulfate-reducing (SRB) bacteria were measured in feces. Ten volunteers were also studied. Results: Total H2 levels in patients were 383–420 mL/day on the basal diet and 1430–1730 mL/day after lactulose administration compared with 35 ± 6 mL/day and 262 ± 65 mL/day, respectively, in controls. Basal breath H2 levels in controls were 27 ± 6 vs. 214 ± 27 mL/day in patients and after lactulose ingestion, 115 ± 18 vs. 370 ± 72 mL/ day. Four controls were methanogenic and had high fecal MB counts. The other controls had high SRB counts and sulfate reduction rates. All patients were nonmethanogenic and had low sulfate reduction rates. Conclusions: Patients with PCI excrete more H2 than controls. In normal subjects, H2 is consumed by MB or SRB; the activity of these bacteria is virtually absent in PCI. This may explain the gas accumulation in these patients.

Groundwater contamination at the Kesterson Reservoir, California: 2. Geochemical parameters influencing selenium mobility

Transport of selenium in groundwater at the Kesterson Reservoir in the Central Valley of California was strongly retarded because of chemical reduction and precipitation mediated by microbial activity. Under such conditions, negative correlations were documented between aqueous Se and Fe2+, Mn, and H2S. Locally, the presence of oxidizing species, notably O2 and NO3, suppressed this reduction, permitting Se mobilization in the shallow aquifer. Selenate, the dominant and most oxidized form of Se, was in electrochemical disequilibrium with subordinate concentrations of selenite. Normally slow inorganic reduction rates were accelerated by microbial activity which utilizes oxidized chemical species including selenate as electron donors during the oxidation of organic matter. Two stratified redox barriers to selenium migration were documented beneath Kesterson: an underlying shallow anoxic zone underlying most of the pond bottom, characterized by high organic content and sulfate reduction, and a deeper dynamic front established by localized O2 infiltration from the overlying ponds and Fe2+ release from aquifer materials. The reducing nature of this deeper aquifer ultimately precludes Se transport to regional groundwater.

Methanogenesis in the hypersaline Solar Lake (Sinai)

Enrichment studies on microbial mat sediments (potential stromatolites) from the hypersaline Solar Lake (Sinai) indicated high numbers of methanogenic bacteria (up to 105 ml−1 sediment) in spite of the high sulfate reduction rate, sulfate concentration and salinity. Among H2/CO2, acetate and monomethylamine, the methylated amine was the preferred substrate. The predominant species enriched was a Methanosarcina sp. The findings indicate that methanogenic bacteria play an important role in hypersaline sulfate-enriched anoxic sediments and stromatolithic microbial mats.

Methanogenesis in the hypersaline Solar Lake (Sinai)

Enrichment studies on microbial mat sediments (potential stromatolites) from the hypersaline Solar Lake (Sinai) indicated high numbers of methanogenic bacteria (up to 105 ml−1 sediment) in spite of the high sulfate reduction rate, sulfate concentration and salinity. Among H2/CO2, acetate and monomethylamine, the methylated amine was the preferred substrate. The predominant species enriched was a Methanosarcina sp. The findings indicate that methanogenic bacteria play an important role in hypersaline sulfate-enriched anoxic sediments and stromatolithic microbial mats.