Activity Of Sulfate-reducing Bacteria Research Articles

Functional bacteria and process metabolism of the Denitrifying Sulfur conversion-associated Enhanced Biological Phosphorus Removal (DS-EBPR) system: An investigation by operating the system from deterioration to restoration

A sulfur conversion-associated Enhanced Biological Phosphorus (P) Removal (EBPR) system is being developed to cater for the increasing needs to treat saline/brackish wastewater resulting from seawater intrusion into groundwater and sewers and frequent use of sulfate coagulants during drinking water treatment, as well as to meet the demand for eutrophication control in warm climate regions. However, the major functional bacteria and metabolism in this emerging biological nutrient removal system are still poorly understood. This study was thus designed to explore the functional microbes and metabolism in this new EBPR system by manipulating the deterioration, failure and restoration of a lab-scale system. This was achieved by changing the mixed liquor suspended solids (MLSS) concentration to monitor and evaluate the relationships among sulfur conversion (including sulfate reduction and sulfate production), P removal, variation in microbial community structures, and stoichiometric parameters. The results show that the stable Denitrifying Sulfur conversion-associated EBPR (DS-EBPR) system was enriched by sulfate-reducing bacteria (SRB) and sulfide-oxidizing bacteria (SOB). These bacteria synergistically participated in this new EBPR process, thereby inducing an appropriate level of sulfur conversion crucial for achieving a stable DS-EBPR performance, i.e. maintaining sulfur conversion intensity at 15–40 mg S/L, corresponding to an optimal sludge concentration of 6.5 g/L. This range of sulfur conversion favors microbial community competition and various energy flows from internal polymers (i.e. polysulfide or elemental sulfur (poly-S2-/S0) and poly-β-hydroxyalkanoates (PHA)) for P removal. If this range was exceeded, the system might deteriorate or even fail due to enrichment of glycogen-accumulating organisms (GAOs). Four methods of restoring the failed system were investigated: increasing the sludge concentration, lowering the salinity or doubling the COD loading, non of which restored SRB and SOB activities for DS-EBPR; only the final novel approach of adding 25 ± 5 mg S/L of external sulfide into the reactor at the beginning of the anoxic phase could efficiently restore the DS-EBPR system from failure. The present study represents a step towards understanding the DS-EBPR metabolism and provides an effective remedial measure for recovering a deteriorating or failed DS-EBPR system.

Comparative Study of Nickel Removal from Synthetic Wastewater by a Sulfate-Reducing Bacteria Filter and a Zero Valent Iron—Sulfate-Reducing Bacteria Filter

ABSTRACTNickel removal from wastewater by a zero valent iron sulfate-reducing bacteria (ZVI-SRB) filter and a sulfate-reducing bacteria (SRB) filter were investigated in this study on the basis of the assumption that integrating SRB with the ZVI system should enhance the removal efficiency of heavy metals from solution. The variation in oxidation–reduction potential (ORP) and pH in the effluent indicated that ZVI provided favorable anaerobic conditions for SRB growth. Measurement of sulfate concentrations confirmed that ZVI promoted sulfate-reducing activity of SRB. When the nickel concentration of influent was 150 mg/l with a HRT of 19h, the nickel-removal efficiency was > 98% for the ZVI-SRB filter and 94.3–96.5% for the SRB filter; with a hydraulic retention time (HRT) of 12h, the nickel-removal efficiency was 95.3–97.0% for the ZVI-SRB filter and 84.3–88.2% for the SRB filter, with a HRT of 6h, the nickel-removal efficiency was 94.2–96.5% for the ZVI-filter and 78.2–81.4% for the SRB filter. This result demonstrated that the ZVI-SRB filter had apparent advantages over the SRB filter, especially when filters were run with a shorter HRT. The scanning electron microscope-energy dispersive X-ray analysis (SEM-EDXA) analysis showed that nickel in the ZVI-SRB filter was mainly removed as nickel sulfide and zero valent nickel. This study demonstrated that a ZVI-SRB filter could be a promising technology for treating wastewater containing heavy metals and bioremediation of contaminated groundwater.

Microbially-mediated fossil-bearing carbonate concretions and their significance for palaeoenvironmental reconstructions: A multi-proxy organic and inorganic geochemical appraisal

Carbonate concretions are widespread within the geological record. However, the lack of recent known analogues creates a need for novel approaches to unravel the major microbial players involved in concretion formation and establish their suitability as palaeoenvironmental recorders. Here, we used a combination of geochemical and geological techniques to study two pyritiferous calcite concretions and compared the results with their host sediment (Toarcian “Posidonia Shale”, 183Ma, SW-Germany).The 13C-depleted nature of the concretion bodies, with average values of δ13Ccarb (−14.8‰), δ13Corg (−32.4‰), and δ13Cn-alkanes (−34.9‰), indicates that sulphate-reducing bacteria (SRB), played a major role in the concretion growth and preservation of the nucleus via the rapid decomposition of organic matter (OM). However, Rock-Eval analyses from both concretions revealed elevated hydrogen indices (HI) in the body and low HI values at the rim. These values suggest that most of the microbial activity did not occur in the concretion body but rather at the rim and at the surface of the nuclei, which generally supports the exceptional preservation of OM in carbonate concretions. Furthermore, enrichment in euhedral pyrite in the concretion rims suggests they were formed through increased activities of iron reducing (FeR) bacteria coupled to a decrease of SRB activity leading towards conditions more favourable to the direct precipitation of pyrite. Despite low δ13C values, the known lipid biomarkers such as acyclic extended isoprenoids or 3β-methyl-hopanes did not reveal evidence of an active methane cycling. The present study emphasises the crucial role of carbonate concretion in OM preservation and highlights their great potential as palaeoenvironmental recorders.

Treatment of antimony mine drainage: challenges and opportunities with special emphasis on mineral adsorption and sulfate reducing bacteria.

The present article summarizes antimony mine distribution, antimony mine drainage generation and environmental impacts, and critically analyses the remediation approach with special emphasis on iron oxidizing bacteria and sulfate reducing bacteria. Most recent research focuses on readily available low-cost adsorbents, such as minerals, wastes, and biosorbents. It is found that iron oxides prepared by chemical methods present superior adsorption ability for Sb(III) and Sb(V). However, this process is more costly and iron oxide activity can be inhibited by plenty of sulfate in antimony mine drainage. In the presence of sulfate reducing bacteria, sulfate can be reduced to sulfide and form Sb(2)S(3) precipitates. However, dissolved oxygen and lack of nutrient source in antimony mine drainage inhibit sulfate reducing bacteria activity. Biogenetic iron oxide minerals from iron corrosion by iron-oxidizing bacteria may prove promising for antimony adsorption, while the micro-environment generated from iron corrosion by iron oxidizing bacteria may provide better growth conditions for symbiotic sulfate reducing bacteria. Finally, based on biogenetic iron oxide adsorption and sulfate reducing bacteria followed by precipitation, the paper suggests an alternative treatment for antimony mine drainage that deserves exploration.

Sulfate reducing bacterial community and in situ activity in mature fine tailings analyzed by real time qPCR and microsensor

Sulfate reducing bacteria (SRB) play significant roles in anaerobic environments in oil sands mature fine tailings (MFTs). Hydrogen sulfide (H2S) is produced during the biological sulfate reduction process. The production of toxic H2S is one of the concerns because it may hinder the landscape remediation efficiency of oil sands tailing ponds. In present study, the in situ activity and the community structure of SRB in MFT and gypsum amended MFT in two settling columns were investigated. Combined techniques of H2S microsensor and dissimilatory sulfite reductase β-subunit (dsrB) genes-based real time quantitative polymerase chain reaction (qPCR) were applied to detect the in situ H2S and the abundance of SRB. A higher diversity of SRB and more H2S were observed in gypsum amended MFT than that in MFT, indicating a higher sulfate reduction activity in gypsum amended MFT; in addition, the activity of SRB varied as depth in both MFT and gypsum amended MFT: the deeper the more H2S produced. Long-term plans for tailings management can be assessed more wisely with the information provided in this study.

Palaeoenvironmental and ecological interpretation of the trace fossil Rhizocorallium based on contained iron framoboids (Upper Devonian, South China)

The trace fossil Rhizocorallium commune is abundant in shallow-marine deposits of the Upper Devonian (Frasnian) Tuqiaozi Formation in Ganxi, Sichuan Province, South China. It consists of U-shaped spreite burrows developed more or less parallel or slightly inclined to the bedding of marly limestone. Four types of iron framboids (mostly oxygenated from pyrite framboids) were found within the Rhizocorallium burrow, including (1) smooth, sheathed spherical, (2) prismatic, (3) octahedral, and (4) pyritohedral submicron crystals. Chemically, the submicron crystals mainly consist of iron, sulphur, oxygen and carbon. The iron framboids represent the stage of evolution of their original pyrite framboids from irregular morphologies and spherical framboids to octahedral and pyritohedral habits due to the activity of sulphate-reducing bacteria. No similar framboids were observed outside Rhizocorallium. Therefore, it is likely that sulphate-reducing bacteria colonised the Rhizocorallium spreite and marginal tube within a dysoxic environment. With increasing degree of oxygenation of pore water, the pyrite framboids were partly oxygenated into iron framboids and by exceptional circumstances preserved the original morphology of the crystals. Furthermore, it is proposed that the investigated Rhizocorallium was constructed by its trace maker for gardening with multifunctional purpose, where different microbial colonies were planted and cultured in the marginal tube and spreite on the mutual basis of food supply and redox conditions. These features indicate that a combined deposit-feeding and gardening model may apply for the construction of Rhizocorallium commune from the Devonian of Ganxi. The responsible trace maker probably was a worm-like organism, such as a polychaete.

Metals-induced functional stress in sulphate-reducing thermophiles.

All toxic metals have been known to inhibit different activities of sulphate-reducing bacteria (SRB) at different concentrations. The present study delineates functional responses of two thermophilic SRB species (Desulfotomaculum reducens-HA1 and Desulfotomaculum hydrothermale-HA2) to toxic metals. Bacterial activity was assessed in terms of sulphate reduction and metal precipitation employing four concentrations (1, 5, 10 and 15 ppm) of three dissolved toxic metals (Cu, Cr and Ni) independently. Both sulphidogenic bacterial species showed results in a very narrow range of fluctuations. In general, bioprecipitation and sulphate reduction were pronounced at lower concentrations (1 and 5 ppm) and got inhibited at higher concentrations (10 and 15 ppm). The order of precipitation and sulphate reduction for the subject metals was Ni > Cr > Cu. The findings of this study will be helpful in developing economical and environmental friendly bioremediation process(es) tending to operate at extreme conditions around the concentrations in indicated suitable metals-loaded effluents.

Role of autochthonous versus detrital micrite in depositional geometries of Middle Triassic carbonate platform systems

Middle Triassic platforms (Formazione di Contrin, Upper Anisian) in the Italian Dolomites, southern Alps, record large changes in carbonate production and depositional geometry. The changes include variation in the abundance of detrital micrite, i.e., allochthonous calcareous mud, relative to the autochthonous micrite, which formed in situ and was syndepositionally lithified. Carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation. Early Anisian low-relief platforms were followed by late Anisian, high-relief buildups, associated with basinal dysoxic-anoxic environments. The geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications, matched by a deepening evolution of the basinal environments. At the same time, the slope sediments record a gradual change from loose detrital micrite, characterizing the lower portion, to autochthonous micrite, dominating the upper part and recording massive syndepositional lithification. The development of the autochthonous micrite was associated with the preservation of significant amounts of organic matter. This sharp increase in automicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments, while anoxic conditions developed in the adjacent organic-rich basin (Moena Formation). The low oxygen level promoted the preservation of organic matter and the activity of sulfate-reducing bacteria, which in turn induced in situ deposition of autochthonous micrite through biomediated processes. This pervasive early cementation and lithification induced the development of steep platform slopes. The conceptual model distilled from this Middle Triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the micrite component.

Numerical modeling and simulation of microbial methanogenesis in geological CO2 storage sites

Abstract A numerical model was developed to assess the feasibility of microbial CH 4 generation in geological CO 2 storage sites. The model accounts for water-rock geochemical reactions, microbial competition between methanogenic microbes and sulfate reducing bacteria (SRB) for H 2 and acetate, and the effect of pH on the activity of microbes. For the sake of analysis, carbohydrates contained in the stimulating nutrient injected along with CO 2 serves as source for the biogenic formation of H 2 and acetate by H 2 -forming fermentative microbes. Simulation results unveiled that the pH buffering effect of carbonate minerals such as calcite is of outmost importance to push methanogenesis reactions. CO 2 injection into a geological formation containing calcite enhances the biogenic supply of H 2 and acetate by providing near optimum pH conditions for the activity of H 2 -forming fermentative microbes. However, when sulfate in the formation water is present in excesses, hydrogenotrophic and acetotrophic SRB outcompete hydrogenotrophic and acetotrophic methanogenic microbes for H 2 and acetate, respectively. This is reflected by the predominant formation of H 2 S and negligible formation of CH 4 . With calcite in the mineral phase, the activity of SRB and methanogenic microbes is governed by their initial concentrations in the formation water. Without calcite in the mineral phase, injection of CO 2 inhibits the activity of hydrogenotrophic and acetotrophic SRB and methanogenic microbes, but not the activity of H 2 -forming fermentative microbes. The activity of H 2 -forming fermentative microbes is not conditioned to the presence of calcite in the mineral phase as their optimum pH falls within the acidic range that results from the injection of CO 2 . Without sufficient amounts of sulfate in the formation water to support the activity of SRB, injection of CO 2 into a geological formation containing calcite favors the biogenic formation of CH 4 via the reduction pathway of CO 2 with H 2 , whereas without CO 2 injection methanogenesis via acetate fermentation is favored. Methanogenesis in geological CO 2 storage sites is possible under controlled CO 2 and stimulating organic nutrients injection. Oil reservoirs containing calcite in the mineral phase and low concentrations of sulfate in the formation water are most suitable for microbial methanogenesis from CO 2 in geological CO 2 storage sites.

INHIBITION OF MICROBIAL SULFATE REDUCTION BY MOLYBDATE

Hydrogen sulfide generation in oil production is a constant cause of concern. In several cases this phenomenon occurs due to the action of sulfate-reducing bacteria. Various methods, including biocides and nitrate addition, have been used to control the activity of these microorganisms, but they are expensive and have side effects. Other inhibition methods, such as the use of molybdate, have received much less attention. This study performed a kinetic test for the inhibition of sulfate reduction, and short-term tests to determine the minimum inhibitory concentration of molybdate in liquid medium containing 10.4 and 20.8 mM of sulfate (1000 mg L-1 and 2000 mg L-1), respectively. An inoculum was prepared from a microbial consortium of sulfate-reducing bacteria dominated by Desulfovibrio vulgaris enriched from produced water from oil wells of the Reconcavo Basin, Brazil. The indicators of bacterial activity used were: sulfate reduction, sulfide production, culture medium color, pH, and redox potential. The tests show that, regardless of the concentration of molybdate, sulfate reduction is inhibited after the first hours of the start of the test. The conversion of sulfate in the kinetic experiment without molybdate is 78%, whereas the average conversion in the experiment with molybdate is approximately 30% in 216 h. The short-term test results show that 0.08 mM (12.8 mg L-1) molybdate, a molar ratio molybdate/sulfate of 0.004, is sufficient to inhibit the activity of sulfate-reducing bacteria for 168 h.

Potential for beneficial application of sulfate reducing bacteria in sulfate containing domestic wastewater treatment.

The activity of sulfate reducing bacteria (SRB) in domestic wastewater treatment plants (WWTP) is often considered as a problem due to H2S formation and potential related odour and corrosion of materials. However, when controlled well, these bacteria can be effectively used in a positive manner for the treatment of wastewater. The main advantages of using SRB in wastewater treatment are: (1) minimal sludge production, (2) reduction of potential pathogens presence, (3) removal of heavy metals and (4) as pre-treatment of anaerobic digestion. These advantages are accessory to efficient and stable COD removal by SRB. Though only a few studies have been conducted on SRB treatment of domestic wastewater, the many studies performed on industrial wastewater provide information on the potential of SRB in domestic wastewater treatment. A key-parameter analyses literature study comprising pH, organic substrates, sulfate, salt, temperature and oxygen revealed that the conditions are well suited for the application of SRB in domestic wastewater treatment. Since the application of SRB in WWTP has environmental benefits its application is worth considering for wastewater treatment, when sulfate is present in the influent.

Bisulfite reductase gene expression of thermophilic sulphate-reducing bacteria from saline connate water of oil reservoirs with high temperature

Connate water (fossil water) is produced during exploitation of oil reservoirs. It may be injected into mature reservoirs during Enhanced Oil Recovery (EOR). Sulphate-reducing bacteria (SRB) are associated with induced corrosion, souring gas, and oil reservoirs. Besides, the mesophilic Desulfovibrionales SRB are common in produced waters. Since the dsrAB transcripts can be related to the activity of SRB, the dsrA expression was quantified in microcosms to assess the SRB present in the reservoir with saline connate waters (RQ and RZ) of two offshore, non-water-flooded, high-temperature oil reservoirs. The retrieved dsrA sequences showed Desulfovibrio, Desulfomicrobium and Desulfohalobium as principal taxa. The dsrB sequences revealed Desulfovibrionales (Desulfotonatronum) and Desulfobacterales (Desulfosarcina and Desulfobulbus) taxa. Most Desulfovibrionales are mesophilic bacteria; nevertheless, sequences of uncultured SRB of this order were found under specific growth conditions at 60 °C in high salinity (110 g l−1 NaCl). Throughout microcosm experiments, the dsrA gene expression dropped dramatically from high salinity to seawater conditions: 9.5 and 7.5 times in RQ and RZ, respectively. The lowest gene expressions were exhibited with 35 g l−1 NaCl at 40 °C and 60 °C (1.4–1.2 × 103 copy number/ug mRNA). The results suggest that sulphate reduction takes place in the connate waters mainly at high salinity and temperature by indigenous obligate halophilic thermophilic Desulfovibrionales SRB.

Sulfate reducing bacteria and their activities in oil sands process-affected water biofilm

Biofilm reactors were constructed to grow stratified multispecies biofilm in oil sands process-affected water (OSPW) supplemented with growth medium. The development of sulfate reducing bacteria (SRB) within the biofilm and the biofilm treatment of OSPW were evaluated. The community structure and potential activity of SRB in the biofilm were investigated with H2S microsensor measurements, dsrB gene-based denaturing gradient gel electrophoresis (DGGE), and the real time quantitative polymerase chain reaction (qPCR). Multispecies biofilm with a thickness of 1000μm was successfully developed on engineered biocarriers. H2S production was observed in the deeper anoxic zone of the biofilm from around 750μm to 1000μm below the bulk water-biofilm interface, revealing sulfate reduction in the deeper zone of the stratified biofilm. The biofilm removed chemical oxygen demand (COD), sulfate, and nitrogen. The study expands current knowledge of biofilm treatment of OSPW and the function of anaerobic SRB in OSPW biofilm, and thus provides information for future bioreactor development in the reclamation of OSPW.

Arsenic bioavailability to rice plant in paddy soil: influence of microbial sulfate reduction

High arsenic (As) mobility in anaerobic paddy soil due to microbial Fe- and As-reducing processes results in As accumulation into rice plants. Sulfur (S) also undergoes microbial reducing processes in the anaerobic paddy soil, while this process interacts with the Fe- and As-reducing processes, forms secondary minerals, and thus influences As mobility in paddy soil. This work was carried out to investigate the role of sulfur and sulfate-reducing bacteria (SRB) in As redox transformation and bioavailability to rice plant in an anaerobic paddy soil. Anaerobic incubation experiments with or without sulfate (SO4 2−) and SRB were carried out to monitor S and iron (Fe) dynamics and their relations to As speciation and release to soil solution. Rice cultivation in pot experiment was then carried out to check the SO4 2− amendment in bioavailability and uptake into rice plants. The inoculation of an enriched SRB community into the sterilized paddy soil increased reduction and release of As to the soil solution after flooding, showing its ability in arsenate (As(V)) as well as SO4 2− reduction to arsenite (As(III)) and sulfide (S2−), respectively. Sulfate addition (2 and 100 mM) into the anaerobic paddy soil increased the reduction of SO4 2− and ferric iron (Fe3+) and resulted to lower dissolved As in the soil solution, which limited As mobility in the paddy soil. Application of SO4 2− (100 mg kg−1) into paddy soil finally decreased the concentration of dissolved As in the soil solution by 23.5 % and also decreased As content in rice roots and iron plaque by 22.6 and 30.5 %, respectively. The results revealed the important role of sulfur and the SRB activity in As speciation and mobility in anaerobic paddy soil, implying a lower As bioavailability to rice plants under sulfur-enriched anaerobic paddy soil, and an efficient way to reduce As accumulation in rice plants by sulfur fertilization in paddy soils.

Release and control of hydrogen sulfide during sludge thermal drying

The release of hydrogen sulfide (H2S) during sludge drying is a major environmental problem because of its toxicity to human health. A series of experiments were performed to investigate the mechanisms and factors controlling the H2S release. Results of this study show that: (1) the biomass and activity of sulfate-reducing bacteria (SRB) in sludge were the major factors controlling the amount of H2S release, (2) the sludge drying temperature had an important effect on both the extent and the timing of H2S release from the sludge, and (3) decreasing sludge pH increased the H2S release. Based on the findings from this study, a new system that integrates sludge drying and H2S gas treatment was developed, by which 97.5% of H2S and 99.7% of smoke released from sludge treatments was eliminated.

Geochemical evidence for the link between sulfate reduction, sulfide oxidation and phosphate accumulation in a Late Cretaceous upwelling system.

BackgroundOn Late Cretaceous Tethyan upwelling sediments from the Mishash/Ghareb Formation (Negev, Israel), bulk geochemical and biomarker analyses were performed to explain the high proportion of phosphates in the lower part and of organic matter (OM) preserved in upper parts of the studied section. The profile is composed of three facies types; the underlying Phosphate Member (PM), the Oil Shale Member (OSM) and the overlying Marl Member (MM).ResultsTotal organic carbon (TOC) contents are highly variable over the whole profile reaching from 0.6% in the MM, to 24.5% in the OSM. Total iron (TFe) varies from 0.1% in the PM to 3.3% in the OSM. Total sulfur (TS) ranges between 0.1% in the MM and 3.4% in the OSM, resulting in a high C/S ratio of 6.5 in the OSM section. A mean proportion of 11.5% total phosphorus (TP) in the PM changed abruptly with the facies to a mean value of only 0.9% in the OSM and the MM.The TOC/TOCOR ratios argue for a high bacterial sulfate reduction activity and in addition, results from fatty acid analyses indicate that the activity of sulfide-oxidizing activity of bacteria was high during deposition of the PM, while decreasing during the deposition of the OSM.ConclusionsThe upwelling conditions effected a high primary productivity and consequently the presence of abundant OM. This, in combination with high sulfate availability in the sediments of the PM resulted in a higher sulfide production due to the activity of sulfate-reducing bacteria. Iron availability was a limiting factor during the deposition of the whole section, affecting the incorporation of S into OM. This resulted in the preservation of a substantial part of OM against microbial degradation due to naturally-occurring sulfurization processes expressed by the high C/S ratio of 6.5 in the OSM.Further, the abundant sulfide in the pore water supported the growth of sulfide-oxidizing bacteria promoting the deposition of P, which amounted to as much as 15% in the PM. These conditions changed drastically from the PM to the OSM, resulting in a significant reduction of the apatite precipitation and a high concentration of reactive S species reacting with the OM.

Biogenic sulfides for sequestration of Cr (VI), COD and sulfate from synthetic wastewater

The aim of this work is to explore the possibility of using mixed culture of mesophilic sulfate-reducing bacteria (SRB) for retrieval of toxic and carcinogenic Cr (VI) from synthetic solution. In order to treat Cr (VI) containing wastewater effectively, SRB culture was adapted to 50 mg/L Cr (VI) and maintained through repeated sub-culturing to enhance the growth and activity of SRB. Batch biosorption experiments were carried out in glass serum vials by cultured SRB, accomplishing the removal of 82.1% Cr (VI), 76.9% sulfate, 85.7% COD under the following optimized conditions: pH 7, hydraulic retention time (HRT) 7 days, temperature 37 °C and initial Cr (VI) concentration of 50 mg/L. Further sorption experiments were conducted on synthetic wastewater under optimal operational conditions and resulted in 89.2% Cr (VI), 81.9% COD and 95.3% sulfate reduction from simulated wastewater. The results of this work contributed to a better understanding of metal uptake by biogenic sulfides and would be beneficial in the development of potential biosorbents that possess high capacities for Cr (VI) uptake from aqueous environments.

Electrochemical characterization of direct electron uptake in electrical microbially influenced corrosion of iron by the lithoautotrophic SRB Desulfopila corrodens strain IS4

Corrosion of iron infrastructure in anoxic environments is commonly ascribed to the metabolic activity of sulfate-reducing bacteria (SRB), which can influence electrochemical processes on the metallic surface. The present study characterizes electron transfer processes at the electrode/microorganism interface of the specialized lithoautotrophic SRB Desulfopila corrodens strain IS4 that is capable of taking up electrons directly from elemental iron, thereby leading to severe corrosion. Electrochemical analysis of the highly corrosive SRB is performed in bio-electrochemical cells operated with artificial seawater under anoxic conditions, complemented by infrared spectroelectrochemical analysis and environmental SEM observations. In order to provide clear insights into electron transfer processes, sterile controls and a non-corrosive hydrogenotrophic control strain are analyzed in parallel. Remarkably, the electron uptake from electrodes by D. corrodens strain IS4 is not restricted to iron serving as the sole electron donor for the microbial metabolism, but instead proceeds also on graphite and doped germanium cathodes. Consequently, a well-defined electrochemical analysis of the electron uptake mechanism is possible, since corrosion precipitates typically observed on iron electrodes are absent on both of the other cathode materials. Direct electron transfer in the absence of artificial electron mediators is achieved at a potential of −0.4V vs. SHE under neutral conditions. Electrochemical and infrared spectroelectrochemical analysis indicated c-type cytochromes as the redox active components associated with the outer membrane to be involved in the direct electron uptake from reduced surfaces by D. corrodens strain IS4.

Methanogenesis produces strong 13C enrichment in stromatolites of Lagoa Salgada, Brazil: a modern analogue for Palaeo-/Neoproterozoic stromatolites?

Holocene stromatolites characterized by unusually positive inorganic δ(13) CPDB values (i.e. up to +16‰) are present in Lagoa Salgada, a seasonally brackish to hypersaline lagoon near Rio de Janeiro (Brazil). Such positive values cannot be explained by phototrophic fixation of CO2 alone, and they suggest that methanogenesis was a dominating process during the growth of the stromatolites. Indeed, up to 5mm methane was measured in the porewater. The archaeal membrane lipid archaeol showing δ(13) C values between -15 and 0‰ suggests that archaea are present and producing methane in the modern lagoon sediment. Moreover, (13) C-depleted hopanoids diplopterol and 3β-methylated C32 17β(H),21β(H)-hopanoic acid (both -40‰) are preserved in lagoon sediments and are most likely derived from aerobic methanotrophic bacteria thriving in the methane-enriched water column. Loss of isotopically light methane through the water column would explain the residual (13) C-enriched pool of dissolved inorganic carbon from where the carbonate constituting the stromatolites precipitated. The predominance of methanogenic archaea in the lagoon is most likely a result of sulphate limitation, suppressing the activity of sulphate-reducing bacteria under brackish conditions in a seasonally humid tropical environment. Indeed, sulphate-reduction activity is very low in the modern sediments. In absence of an efficient carbonate-inducing metabolic process, we propose that stromatolite formation in Lagoa Salgada was abiotically induced, while the (13) C-enriched organic and inorganic carbon pools are due to methanogenesis. Unusually, (13) C-enriched stromatolitic deposits also appear in the geological record of prolonged periods in the Palaeo- and Neoproterozoic. Lagoa Salgada represents a possible modern analogue to conditions that may have been widespread in the Proterozoic, at times when low sulphate concentrations in sea water allowed methanogens to prevail over sulphate-reducing bacteria.

Anaerobic Microbial Activities of a Nigerian Onshore Oil Production Facility that Uses Underground Water with Zero Sulfate Concentration for Injection

Aim: To evaluate the anaerobic microbial activities and souring potential of a Nigerian onshore oil production facility that uses zero sulfate underground water for injection. Methodology: Key functional group activities such as the ability to reduce sulfate and generate sulfide by sulfate reducing bacteria (SRB), the ability to reduce nitrate to nitrite by the heterotrophic nitrate reducing bacteria (hNRB) and the ability to reduce nitrate and oxidize sulfide by sulfide oxidizing, nitrate reducing bacteria (so - NRB) were determined in samples using CSB - K medium. Results: Lactate utilizing SRBs and hNRBs were found to be common in most oil field samples while the activities of so - NRBs were limited to very few sam ples. It was also observed that the underground water with zero sulfate concentration and negligible microbial activity poses no souring risk to the oil field under investigation. The produced water and oil samples from the facility though with considerabl e populations and activities of SRBs also recorded negligible concentration of sulfate and some organic nutrients and therefore are not likely to pose some souring risks to the oil facility under investigation. Conclusion: From our investigation, it is evident that the zero sulfate underground water with negligible SRB populations and activities poses no souring risks to the facility under investigation