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The reactive MgO (r-MgO)-microbial curing technology can not only effectively improve the strength of electrolytic manganese residue (EMR) but also repair heavy metal ions. By conducting unconfined compressive strength (UCS) test, heavy metal leaching test, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP), the effects of the type and concentration of sulfate on the strength and repair of heavy metals of the cured EMR under drying–wetting (DW) cycles were studied, and the strength and the evolution mechanism of heavy metal remediation is elucidated. The results indicate the following: With the increase in the number of DW cycles, the dry density of the samples in high concentration of MgSO4 first increased slightly and then decreased gradually and became stable. The dry density of the samples in Na2SO4, low concentration of MgSO4, and water generally showed a downward trend. The pH of the soaking solution slightly decreased, and the leaching concentration of heavy metal Mn2+ ions always remained at a low level. The UCS of the samples in MgSO4 first increased slightly and then decreased gradually, and then became stable. The amount of cured products first increased and then decreased, and the size of internal pores first decreased and then increased. The UCS of the samples in Na2SO4 and water gradually decreased and became stable. The amount of cured products gradually decreased, and the size of internal pores gradually increased. The research results provide a theoretical basis for the evaluation of resistance against the sulfate corrosion of cured EMR under DW cycles. [ABSTRACT FROM AUTHOR]

Sediment historically impacted by acid mine drainage was exposed to different initial pH and electron donors to investigate the effect that both conditions had on the performance and fingerprint of the community from naturally acidic sediments. Batch experiments were fed with either acetate, lactate, or glycerol at initial pH of 5, 4, or 3, under sulfate-reducing conditions. The performance results indicated that sulfide production efficiency was above 85% in the treatments fed with lactate and glycerol at pH 5 and 4. However, acetate consumption efficiency was greater than 85% only in the treatments with acetate at pH 5 and lactate at pH 5 and 4. Glycerol fed treatments successfully produced sulfide even at initial pH = 3. Sulfide production rates were related to the initial pH in treatments fed with lactate and acetate and independent of the pH in the glycerol fed treatments. 16S rRNA gene T-RFLP analysis of the enriched communities indicated that the initial pH could explain the differences of the microbial community fingerprint obtained after 90 days. This study points out the fact that acidic stress is a heavy burden for the development of sulfate-reducing microorganisms, especially for those that use acetate as substrate. [ABSTRACT FROM AUTHOR]

Mercury (Hg) transport and methylmercury (MeHg) production in riverbank sediments are complex processes influenced by site-specific physical and biogeochemical conditions. The South River watershed in VA, USA, contains elevated concentrations of Hg in riverbank and floodplain sediments, which has the potential to methylate. The role of specific organic carbon sources in promoting methylation reactions in natural sediments under dynamic flow conditions is not well understood. Four saturated column experiments were conducted, including a control column, which received South River water as an influent solution, and three columns that received South River water amended with: acetate (5.8 mM); lactate (5.7 mM); and lactate (5.7 mM) with SO42−(10.1 mM). The amendments were selected to promote growth of different microorganisms to gain an understanding of the microbial processes, controlling rates of methylation. The column receiving lactate and SO42−had the highest MeHg concentrations in the effluent and in the pore water near the effluent at 1.8 and 4.9 μg L−1, respectively. At the cessation of the column experiments, the lactate–sulfate column sediments contained the highest populations of enumerable sulfur-reducing bacteria and the highest solid-phase MeHg at 530 ± 100 ng g−1dry wt. from the interval closest to the influent. The results suggest that the form and availability of electron donors and acceptors are primary factors controlling rates of methylation in the South River sediment. [ABSTRACT FROM AUTHOR]

Sulfur and oxygen isotope fractionation of elemental sulfur disproportionation at anaerobic haloalkaline conditions was evaluated for the first time. Isotope enrichment factors of the strains Desulfurivibrio alkaliphilus and Dethiobacter alkaliphilus growing at pH 9 or 10 were −0.9‰ to −1‰ for sulfide (34ϵ), +3.6‰ to +4.7‰ for sulfate (34ϵ), and +3.5‰ to +7.7‰ for oxygen in sulfate (18ϵ). These values are significantly smaller compared to previously published values of sulfur disproportionators at neutral pH. We propose that this discrepancy is caused by masking effects due to preferential formation of polysulfides at high pH leading to accelerated internal sulfur turnover rates, but cannot rule out distinct isotope effects due to specific enzymatic disproportionation reactions under haloalkaline conditions. The results imply that the microbial sulfur cycle in haloalkaline environments is characterized by specific stable sulfur and oxygen isotope patterns. [ABSTRACT FROM AUTHOR]

The groundwater system in Olkiluoto, Finland, is stratified with a mixing layer at a depth of approximately 300 m between sulphate-rich, methane-poor and sulphate-poor, methane-rich groundwaters. New sequence library data obtained by 454 pyrotag sequencing of the v4v6 16S rDNA region indicated that sulphate-reducing bacteria (SRB) dominated the mixing layer while SRB could not be detected in the deep sulphate-poor groundwater samples. With the indispensable support of the sequence data, it could be demonstrated that sulphate was the only component needed to trigger a very large community transition in deep sulphate-poor, methane-rich groundwater from a non-sulphate-reducing community comprisingHydrogenophaga,Pseudomonas,Thiobacillus,Fusibacter, andLutibacterto a sulphate-reducing community withDesulfobacula,Desulfovibrio,Desufobulbaceae,Desulfobacterium,Desulfosporosinus, andDesulfotignum. Experiments with biofilms and planktonic microorganisms in flow cells underin situconditions confirmed that adding sulphate to the sulphate-poor groundwater generated growth of cultivable SRB and detectable SRB-related sequences. It was also found that the 16S rDNA diversity of the biofilms was conserved over 103 d and that there was great similarity in diversity between the microorganisms in the biofilms and in the flowing groundwater. This work demonstrates that the presence/absence of only one geochemical parameter, i.e., sulphate, in the groundwater significantly influenced the diversity of the investigated subterranean microbial community. [ABSTRACT FROM PUBLISHER]

Predicting metabolic rates and population sizes of microorganisms in natural environments is a central problem in geomicrobiology. Such predictions can be made on the basis of a thermodynamically consistent rate law that accounts for both kinetic and thermodynamic controls on microbial metabolism. Application of the rate law requires kinetic and growth parameters, the values of which have been determined for pure and mixed cultures growing in laboratory reactors. However, not all parameter values derived from laboratory studies can be validly applied to the environment. This article illustrates a best-choice approach for extrapolating experimentally-derived parameter values to natural environments, using microbial sulfate reduction coupled to acetate oxidation as an example. We compiled kinetic and growth parameters determined by previous laboratory studies and evaluated their applicability to natural environments. Our results suggest that some parameters, such as rate constants and maximum growth yields, can be applied directly to the environment; others, such as half-saturation constants and specific maintenance rates, are best determined using samples recovered from the environment of interest. The best-choice parameter values were applied to simulation of acetotrophic sulfate reduction in the sediments of a freshwater lake. Our analysis shows that the best-choice approach reduces the tasks of parameter fitting and simplifies the modeling exercise. The proposed approach also ensures that parameters in use are consistent with the physiology of indigenous microorganisms, and relevant to the environment of interest. [ABSTRACT FROM PUBLISHER]

A soil enrichment culture of the sulfate-reducers Desulfosporosinus auripigmenti and Citrobacter freundii and of fermentative bacteria from a former uranium-mining site was studied for its metal retention potential by promoting metal sulfide precipitation. The culture could tolerate up to 30 mM Ni and 40 mM Co. XRD and TEM analyses revealed the formation of amorphous NiS together with nanocrystalline, metastable α-NiS, and nanocrystalline cobalt pentlandite. The α-NiS with a grain size of 5 nm shows probably an example of size-dependent phase stability and/or specific biomineralization precipitation paths. Detailed mineralogical characterizations are necessary to correctly assess the mineral inventory and thus metal bioavailability. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) lake of Xiang Mountain in Anhui Province, China, was characterized by acidic waters (pH around 2.8) containing high concentrations of soluble metals and sulfate. To investigate the function and dynamics of this extreme ecosystem, four water samples were collected from the lake in the fall of 2010. The acidophilic community structure was analyzed by molecular approaches, and bacterial and archaeal clone libraries of 16S rRNA genes were constructed. In contrast to dominance of chemolithotrophic acidophiles in typical AMD environments, autotrophic iron/sulfur-oxidizing bacteria were detected in only one sample with low abundance. Unexpectedly, the Cyanobacteria group was the predominant in all four samples (54.9%−77%). Chemoheterotrophs Acidiphilium and Acidisphaera were also abundant. These two heterotrophic groups contain bacteriochlorophyll that can perform photosynthesis, an advantage to grow and survive in such oligotrophic acidic environments. Only two clone sequences related to Legionella (2.8% of the total clones) were recovered from one sample in sharp contrast to its higher abundance (12.7%) in the summer of 2009. All archaeal sequences were affiliated to the phylum Crenarchaeota. The results of statistical analysis suggested that the water chemistry of the AMD lake controlled microbial composition of the AMD ecosystem. [ABSTRACT FROM AUTHOR]

The long-term safety of final disposal of spent nuclear fuel in the deep geosphere is dependent on stability of biogeochemical conditions at the disposal site. Microbial processes, such as sulphate reduction and methanogenesis, may have profound effects on site biogeochemistry. In this study, sulphate-reducing bacteria and methane-producing archaea were investigated at depths ranging from 68 to 545 m in crystalline rock fractures at an intended spent nuclear fuel disposal site in Olkiluoto, Finland. Denaturing gradient gel electrophoresis detected diverse sulphate-reducing bacterial communities in all samples. Although the number of dsrB gene copies was below 103 copies ml−1 in all analyzed samples according to real-time quantitative PCR, their abundance was highest in samples that had the highest sulphate concentrations. Several distinct mcrA gene fragments were also recovered from most of the analyzed samples by cloning, although the number of methanogens was lower than that of sulphate-reducing bacteria when measured by mcrA-targeted quantitative PCR. The detected gene fragments were most closely related to sequences obtained from aquatic and deep subsurface environments. Results imply that sulphate reduction, methanogenesis, and anaerobic methane oxidation may all take place in the Olkiluoto deep geobiosphere. [ABSTRACT FROM AUTHOR]

To evaluate the contribution of Sulfate-Reducing Bacteria (SRB) to the carbon flux from marine salterns, sulfate reducing activity (SRA) was measured for a year (Sept 2000-Aug 2001) This covered the pre-monsoon period (Feb-May), the monsoon (June-Sept) and the post-monsoon (Oct-Jan) in the salterns of Ribandar, Goa, India. Sulphate reduction was examined to gain insights into the decomposition characteristics (kinetics) of organic carbon; this connection is based on the theory of stoichiometric coupling between anaerobic carbon degradation and sulphate reduction to sulphide. SRA was measured using radiotracer techniques. Spatially, recalcitrance of the substrates, as depicted by the reaction rate coefficient (k), increased with depth, except during the monsoons. The values ranged from 0.0061 during the pre monsoon to 0.06 month-1 during the post-monsoon at 5-10 cm depth. The recalcitrance was highest at the surface during the monsoons at a k value of 0.014 month-1. The anaerobic degradation of labile organic matter followed first order kinetics or G model during non-monsoon seasons when the substrate was limiting due to closure of the system to the addition of extraneous source of organic matter. However, the integrated recalcitrance or the reaction rate coefficient was much higher during the post monsoon at 0.642 month-1 compared to 0.053 month-1 during the pre-monsoon season. Interestingly, the reaction rate followed zero-order kinetics when the substrate was non-limiting during monsoon due to exposure to external inputs. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess the weathering of biotite under conditions simulating an active bioleaching environment. Finely ground biotite was contacted with Acidithiobacillus ferrooxidans culture solutions for up to 120 days. Biotite was altered under these conditions to interstratified structures comprised of mixed layers of biotite and vermiculite. Interlayer K in biotite was released upon weathering and precipitated with ferric iron and sulfate to form jarosite. Substantial dissolution of biotite was also associated with weathering. The data demonstrate that exposed, biotite-rich rocks in mine tailings and heap and dump leaching systems can undergo acid mediated solubilization and structural changes, which are coupled with the formation of expansive, vermiculite-like minerals and jarosite precipitation. [ABSTRACT FROM AUTHOR]

The sulfur chemical speciation in extracellular and intracellular sulfur globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus were investigated with an integrated approach including scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). The results indicated that both strains can accumulate extracellular sulfur globules when grown on thiosulfate, and the major sulfur chemical speciation of which were S8 for A. ferrooxidans and mixture of ring sulfur and polythionate for A. caldus, respectively. In contrast, A. ferrooxidans can accumulate both linear sulfur and S8 internally when grown with sulfur powder and thiosulfate, whereas A. caldus did not accumulate intracellular sulfur globules. In addition, the fitted results of sulfur K-edge XANES spectra indicated that the reduced glutathione (containing thiols groups) were involved in sulfur bio-oxidation of both strains and the tetrathionate were the intermediate products during thiosulfate metabolism by two strains. [ABSTRACT FROM AUTHOR]

The biological reduction of soluble U(VI) to the less soluble U(IV) has been proposed as a strategy to remediate uranium-contaminated sites. However, the majority of the contaminated sites contain, in addition to U(VI), competing electron acceptors (CEAs) that can either enhance or inhibit U(VI) reduction. Desulfotomaculum reducens MI-1 is a sulfate-reducing bacterium able to reduce a variety of electron acceptors including U(VI). We characterized U(VI) reduction by D. reducens in the presence of pyruvate and three CEAs: sulfate, nitrate or soluble ferric iron. In the presence of sulfate or ferric iron and U(VI), cell growth was driven by respiration of the CEA. Nitrate was not used as an electron acceptor for growth and vegetative cells grew instead by fermenting pyruvate. Sulfate remaining after sulfate reduction has ceased or the presence of nitrate did not affect U(VI) reduction. However, in the case of sulfate, the addition of H2 after the depletion of pyruvate greatly enhanced U(VI) reduction. Contrary to sulfate and nitrate, the presence of Fe(II), the product of Fe(III) reduction, abolished U(VI) reduction. The results from this investigation suggest that this microorganism and others with similar characteristics may play a role in U(VI) bioremediation efforts but only after the soluble Fe(II) produced by Fe(III) reduction has been advected away. [ABSTRACT FROM AUTHOR]

Sediments in the Indian Ocean off the coast of the Indonesian island Sumatra were sampled at 25 stations in high resolution near the sediment surface and at three stations up to a maximum depth of 12 meter below seafloor (mbsf) for a quantitative microbial community analysis. Total cell counts were determined applying two different protocols including SYBR Green II as fluorescent staining dye. Total cell counts without detaching cells from sediment particles were 109 cells/ mL sediments at the sediment surface with little variation between all stations. They decreased to 108 cells/ mL at 0.2 to 0.4 mbsf and to 107 cells/ mL below 6 mbsf. The total cell counts after detaching cells from sediment particles were up to one order of magnitude lower above 6 mbsf and showed similar values below. This difference for the two protocols can be explained by a loss of cells during the detachment procedure and/or counting of unspecific signals without detaching cells from sediment particles. Particular phylogenetic and physiological prokaryotic groups were quantified by quantitative, real-time PCR (Q-PCR) targeting 16S rRNA and functional genes. Archaea and Bacteria were found overall in similar 16S rRNA gene copy numbers in the range of the total cell counts at all sediment depths, thus, neither Archaea nor Bacteria could be considered as dominant. The eukaryotic 18S rRNA gene occurred in two orders of magnitude lower numbers than prokaryotic 16S rRNA genes. Fe(III)- and Mn(IV)-reducing bacteria (16S rRNA gene of Geobacteraceae) and sulfate-reducing bacteria (functional gene dsrA) were detected in variable (up to 108 gene copies/ mL sediment) but in always significantly lower numbers than total Bacteria. The proportion of sulfate reducers on the prokaryotic community was between 0.2 and 19%. Calculated aereal sulfate reduction rates were overall low with values between 0.002 and 0.027 mmol m- 2a- 1, resulting in sulfate reduction rates per cell of 0.0007 and 0.81 fmol cell- 1 a- 1, similar to published data for other deeply buried marine sediments. Methanogenesis did not seem to play a big role since methane was detected only below 6.5 mbsf, and the functional gene of methanogens and anaerobic methanotrophs mcrA could not be detected in any sample. [ABSTRACT FROM AUTHOR]

In deep subsurface sediments of the Juan de Fuca Ridge Flank, porewater acetate that is depleted in 13C relative to sedimentary organic matter indicates an acetogenic component to total acetate production. Thermodynamic calculations indicate common fermentation products or lignin monomers as potential substrates for acetogenesis. The classic autotrophic reaction may contribute as well, provided that dihydrogen (H2) concentrations are not drawn down to the thermodynamic thresholds of the energetically more favorable processes of sulfate reduction and methanogenesis. A high diversity of novel formyl tetrahydrofolate synthetase (fhs) genes throughout the upper half of the sediment column indicates the genetic potential for acetogenesis. Our results suggest that a substantial fraction of the acetate produced in marine sediment porewaters may derive from acetogenesis, in addition to the conventionally invoked sources fermentation and sulfate reduction. [ABSTRACT FROM AUTHOR]

Despite its importance in carbon mineralization pathways, relatively little is known about sulfate reduction along a continental slope and rise. We investigated the temporal and spatial variations and controls of sulfate reduction rates (SRRs) in the continental margin sediment of the Ulleung basin (UB), off the southeast Korean upwelling system in the East Sea. SRRs ranged from 1.22 to 8.07 mmol m-2 d-1 at the slope sites and from 0.69 to 3.18 mmol m-2 d-1 at the basin sites. These values were exceptionally higher than those observed within other marginal seas and were comparable to SRR values at the same depth range in the Peruvian and Chilean upwelling systems. The high sulfate reduction in the UB was attributable to enhanced primary production in the water column associated with coastal upwelling and a high export flux of large organic particles into the basin via the Ulleung warm eddy. The depth integrated SRR was approximately 4 times higher in the highly productive spring (4.91 ± 2.55 mmol m-2 d-1) than during the summer, which exhibited a stratified water column (1.28 ± 0.48 mmol m-2 d-1). In the meantime, despite the high organic carbon content (> 2.5% dry wt.) in the UB, the SRR was consistently suppressed in the Mn oxide-enriched (174 μ mol cm-3) surface sediments of the continental rise. Overall, these results indicate that the production of organic carbon in the water column and its subsequent deposition on the seafloor is the primary source controlling the temporal variability of sulfate reduction, whereas the Mn oxides that were enriched in the basin are responsible for the spatial variability of the SRR in the UB. Carbon oxidation in the UB accounted for approximately 30% of primary production and approximately 60% of the export flux, indicating that the continental slope and rise of the UB is a region of rapid organic carbon turnover and nutrient regeneration. [ABSTRACT FROM AUTHOR]

The effect of bacteriogenic iron oxides (BIOS) on microbial community structure in subterranean igneous rock aquifers was evaluated. Of interest was to understand how bacteria are partitioned between groundwater and BIOS and to determined whether such spatial separation within the same environment confers niche-specific selectivity. The distribution of the methane-oxidizing and sulphate-reducing bacteria (SRB) was examined closely because the former are important for redox maintenance in this predominantly anaerobic environment. The SRB are ecologically important in organic carbon mineralization representing the most abundant and diverse metabolic group in the aquifers. The corrosive hydrogen sulphide they produce poses a threat to the integrity of the copper canisters that will store spent nuclear waste deposited in these aquifers. Widespread deposits of BIOS occur at microaerophilic interfaces where anaerobic ground water interacts with oxygen. Applying molecular techniques, BIOS deposited along microaerophilic zones in the aquifers was found to select for bacterial phylotypes normally not predominant in groundwater. More than 70% of the SRB occurred in association with the BIOS-rich zones. The native SRB widespread in the aquifers poorly colonized environments associated with BIOS. As much as 50% of the total bacterial counts present in the BIOS communities could be identified as type I methanotrophs predominated by filamentous forms. In addition to biogeochemical factors such as salinity and depth, this study suggests that BIOS environments may constitute a distinct niche with unique properties that enrich for microorganisms different from those commonly reported in the non-BIOS aquifers. [ABSTRACT FROM AUTHOR]

The purpose of the study was to produce schwertmannite (ideally Fe8O8(OH)6(SO4)) and jarosite ((K, NH4, H3O)Fe3(SO4)2 (OH)6) through bacterial iron oxidation and use these Fe(III)-hydroxysulfates as electron acceptors for sulfate-reducing microorganisms. Iron-oxidizing microorganisms were used to oxidize soluble Fe(II) to Fe(III) at pH ∼2, resulting in precipitation of schwertmannite and jarosite. The precipitates were used as solid-phase electron acceptors for sulfate-reducing bacteria with lactate as the electron donor under mesophilic (22°C) and thermophilic (45 and 60°C) anaerobic conditions. Gypsum (CaSO4·2H2O) was also used as a reference electron acceptor because it is moderately soluble and previous studies had shown that the sulfate entity was reduced to sulfide by sulfate-reducing bacteria. The formation of greigite (Fe3S4) from schwertmannite was verified with X-ray diffraction after 2 weeks of incubation in the 60°C sulfate-reducing culture. Greigite was also identified in solids from media that had gypsum and jarosite as the sole sulfate source but was much less abundant. In all cases, the relative amount and crystallinity of greigite increased with the incubation temperature. The results showed that Fe(III)-hydroxysulfates are not biologically stable and can be reduced to Fe-sulfides under anoxic conditions. The cycling of Fe between oxidized and reduced solid phases may also involve solubilization or immobilization of potentially toxic metals or other ions if they are associated with precipitates through sorption or solid solution. [ABSTRACT FROM AUTHOR]

We isolated an acid-tolerant sulfate-reducing bacterium, GBSRB4.2, from coal mine-derived acidic mine drainage (AMD)-derived sediments. Sequence analysis of partial 16S rRNA gene of GBSRB4.2 revealed that it was affiliated with the genus Desulfosporosinus. GBSRB4.2 reduced sulfate, Fe(III) (hydr)oxide, Mn(IV) oxide, and U(VI) in acidic solutions (pH 4.2). Sulfate, Fe(III), and Mn(IV) but not U(VI) bioreduction led to an increase in the pH of acidic solutions and concurrent hydrolysis and precipitation of dissolved Al3+. Reduction of Fe(III), Mn(IV), and U(VI) in sulfate-free solutions revealed that these metals are enzymatically reduced by GBSRB4.2. GBSRB4.2 reduced U(VI) in groundwater from a radionuclide-contaminated aquifer more rapidly at pH 4.4 than at pH 7.1, possibly due to the formation of poorly bioreducible Ca-U(VI)-CO3 complexes in the pH 7.1 groundwater. [ABSTRACT FROM AUTHOR]

Acid mine drainage is a widespread environmental problem and is characterized by elevated proton, sulfate, and dissolved iron concentrations. To understand the driving forces behind the attenuation of AMD, we compared microcosms using sediment and groundwater collected at Davis Mine, Massachusetts, a site where both generation and attenuation of AMD occur. A shift in key geochemical parameters over time was due to the natural microbial population, which was supported by detailed molecular biology results. The attenuation of AMD was stimulated through amendment with glycerol, with nitrogen and phosphorous, or with algae extract, but not by wood chips, suggesting the addition of different organic electron donors as a bioremediation strategy. [ABSTRACT FROM AUTHOR]

The importance of crustal fluid chemical composition in driving the marine deep subseafloor biosphere was examined in northeast Pacific ridge-flank sediments. At IODP Site U1301, sulfate from crustal fluids diffuses into overlying sediments, forming a transition zone where sulfate meets in situ-produced methane. Enhanced cell counts and metabolic activity suggest that sulfate stimulates microbial respiration, specifically anaerobic methane oxidation coupled to sulfate reduction. Cell counts and activity are also elevated in basement-near layers. Owing to the worldwide expansion of the crustal aquifer, we postulate that crustal fluids may fuel the marine deep subseafloor biosphere on a global scale. [ABSTRACT FROM AUTHOR]

This paper reviews the geomicrobiological role of sulphate-reducing bacteria (SRB) in environments contaminated with petroleum products and describes the habitats of SRB and their capacity for bioremediation in anaerobic conditions. Moreover, the participation of SRB in biocorrosion and formation of different minerals and sediments is discussed. [ABSTRACT FROM AUTHOR]

Sulfate-reducing bacteria contribute considerably to the degradation of organic matter in sewage contaminated soils, particularly below leaking sewers. Molybdate as a specific inhibitor of sulfate reduction is known to be present in sewage. Its influence on sulfur isotope fractionation during sulfate reduction was explored in batch experiments with pure cultures of Desulfovibrio desulfuricans and with natural populations enriched from sewage-contaminated soil. Results with D. desulfuricans show that molybdate (0.1 mmol/l) caused a decrease of 6‰ in the isotope enrichment factor compared to an uninhibited control. The decrease in sulfur isotope fractionation may be explained by a depletion of ATP resulting in a lesser amount of activated sulfate available for sulfate reduction in the organism. Experiments carried out at 15 and 37°C reveal a decrease of about 4‰ in the isotope enrichment factor at the low temperature, which is attributed to limited uptake of sulfate. The sulfate-reducing enrichment cultures have fractionated sulfur isotopes to an extent that lies within the range of that produced by the pure cultures of Desulfovibrio desulfuricans (ℇ = -13.5‰). Furthermore, the results demonstrate the influence of bacterial growth on development of the isotope enrichment factor and its possible changes during a batch-type experiment. [ABSTRACT FROM AUTHOR]

The distribution of sulphate-reducing bacteria (SRB) in the sediments of the Colne River estuary, Essex, UK covering different saline concentrations of sediment porewater was investigated by the use of quantitative competitive PCR. Here, we show that a new PCR primer set and a new quantitative method using PCR are useful tools for the detection and the enumeration of SRB in natural environments. A PCR primer set selective for the dissimilatory sulphite reductase gene ( dsr ) of SRB was designed. PCR amplification using the single set of dsr -specific primers resulted in PCR products of the expected size from all 27 SRB strains tested, including Gram-negative and positive species. Sixty clones derived from sediment DNA using the primers were sequenced and all were closely related with the predicted dsr of SRB. These results indicate that PCR using the newly designed primer set are useful for the selective detection of SRB from a natural sample. This primer set was used to estimate cell numbers by dsr selective competitive PCR using a competitor, which was about 20% shorter than the targeted region of dsr . This procedure was applied to sediment samples from the River Colne estuary, Essex, UK together with simultaneous measurement of in situ rates of sulphate reduction. High densities of SRB ranging from 0.2 - 5.7 × 10 8 cells ml -1 wet sediment were estimated by the competitive PCR assuming that all SRB have a single copy of dsr . Using these estimates cell specific sulphate reduction rates of 10 -17 to 10 -15 mol of SO 4 2- cell -1 day -1 were calculated, which is within the range of, or lower than, those previously reported for pure cultures of SRB. Our results show that the newly developed competitive PCR technique targeted to dsr is a powerful tool for rapid and reproducible estimation of SRB numbers in situ and is superior to the use of culture-dependent techniques. [ABSTRACT FROM AUTHOR]

In situ experiments were conducted in order to quantify sulfate reduction kinetics among thermophilic prokaryotes thriving in hydrothermal springs of Yellowstone National Park (USA). Selected springs were sampled based on their varied physicochemical characteristics in order to identify the effect of extreme environmental determinants over sulfate reduction. Reduction rates range from 1 to 483 nmol cm -3 d -1 in various springs with no correlation observed between sulfate reduction rate and pH or sulfate concentration of spring waters. A weak negative correlation with temperature exists though. Results from slurry incubation experiments show that both the apparent activation energy and the half-saturation constant are site specific. Activation energies of 17, 38, and 119 kJ mol -1 were determined in three different springs whereas the half-saturation constant values of 1.24 ± 0.90 and 3.17 ± 1.02 mM were calculated for two of the sampled springs. Such variations in activity and kinetic parameters may depict a change in the microbial population in different springs, or the response of microbial assemblages to changing physicochemical conditions. In the latter case the sulfate reducers must be highly adaptive to changing environmental conditions. [ABSTRACT FROM AUTHOR]

Cretaceous rock formations have been shown to harbor extant sulfate-reducing microbial communities. At these sites, microbial activity is concentrated at rock interfaces where there is likely a diffusion of nutrients from low permeability organic rich shales to higher permeability sandstones. This study was undertaken to further characterize this process and to determine the components of shale that provide electron donors for sulfate reduction activity. To this end, samples of Cretaceous sandstones were incubated with ground shales from available depths at the Cerro Negro exploratory drilling site in northwestern New Mexico. Both sulfate consumption as an indicator of sulfate reduction and acetate production were stimulated in the sandstone-shale incubations. The greatest levels of stimulation were observed with shales originally closest to the lower sandstone-shale interface and a strong correlation was observed between shale organic carbon and microbial activity. These results suggested that the organic matter in shale was supplying the needed electron donor for the sulfate-reducing microbial community. Further evidence for this interpretation was provided when a pure culture of Acetobacterium psammolithicum, an acetogen isolated from this site, was stimulated to produce acetate by the addition of autoclaved shales. To investigate the components in shale that were responsible for stimulating microbial activity, we extracted shale organic material. Aqueous extracts and to a lesser extent neutral ether extractions stimulated activity although neither to the same extent as the shale itself. Alkaline aqueous extracts were fractionated using XAD-7 resin. Each of the fractions contributed to some degree, but the greatest stimulation in microbial activity was attributed to both the hydrophilic eluate and to the fulvic acid fraction. These data indicate that a relatively complex group of organic compounds supply electron donors to the sandstone microbial communities. [ABSTRACT FROM AUTHOR]