Microbial release of 226Ra2+ from (Ba,Ra)SO4 sludges from uranium mine wastes.

226Ra2+ is removed from uranium mine effluents by coprecipitation with BaSO4. (Ba,Ra)SO4 sludge samples from two Canadian mine sites were found to contain active heterotrophic populations of aerobic, anaerobic, denitrifying, and sulfate-reducing bacteria. Under laboratory conditions, sulfate reduction occurred in batch cultures when carbon sources such as acetate, glucose, glycollate, lactate, or pyruvate were added to samples of (Ba,Ra)SO4 sludge. No external sources of nitrogen or phosphate were required for this activity. Further studies with lactate supplementation showed that once the soluble SO4(2-) in the overlying water was depleted, Ba2+ and 226Ra2+ were dissolved from the (Ba,Ra)SO4 sludge, with the concurrent production of S2-. Levels of dissolved 226Ra2+ reached approximately 400 Bq/liter after 10 weeks of incubation. Results suggest that the ultimate disposal of these sludges must maintain conditions to minimize the activity of the indigenous sulfate-reducing bacteria to ensure that unacceptably high levels of 226Ra2+ are not released to the environment.     

Sulfate-Reducing Bacteria Release Barium and Radium from Naturally Occurring Radioactive Material in Oil-Field Barite

Scale and sludge deposits formed during oil production can contain elevated levels of Ra, often coprecipitated with barium sulfate (barite). The potential for sulfate-reducing bacteria to release ²²⁶Ra and Ba (a Ra analog) from oil-field barite was evaluated. The concentration of dissolved Ba increased when samples containing pipe scale, tank sludge, or oil-field brine pond sediment were incubated with sulfate-reducing bacteria Desulfovibrio sp., Str LZK1, isolated from an oil-field brine pond. However, Ba release was not stoichiometric with sulfide production in oil-field samples, and < 0.1% of the Ba was released. Potential for the release of ²²⁶Ra was demonstrated, and the ²²⁶Ra release associated with sulfate-reducing activity was predictable from the amount of Ba released. As with Ba, only a fraction of the ²²⁶Ra expected from the amount of sulfide produced was released, and most of the Ra remained associated with the solid material.     

Field-scale isotopic labeling of phospholipid fatty acids from acetate-degrading sulfate-reducing bacteria

Isotopic labeling of biomarker molecules is a technique applied to link microbial community structure with activity. Previously, we successfully labeled phospholipid fatty acids (PLFA) of suspended nitrate-reducing bacteria in an aquifer. However, the application of the method to low energy-yielding processes such as sulfate reduction, and extension of the analysis to attached communities remained to be studied. To test the feasibility of the latter application, an anoxic test solution of 500 l of groundwater with addition of 0.5 mM Br- as a conservative tracer, 1.1 mM SO4(2-), and 2.0 mM [2-13C]acetate was injected in the transition zone of a petroleum hydrocarbon-contaminated aquifer where sulfate-reducing and methanogenic conditions prevailed. Thousand liters of test solution/groundwater mixture were extracted in a stepwise fashion after 2-46 h incubation. Computed apparent first-order rate coefficients were 0.31+/-0.04 day(-1) for acetate and 0.34+/-0.05 day(-1) for SO4(2-) consumption. The delta13C increased from -71.03 per thousand to +3352.50 per thousand in CH4 and from -16.15 per thousand to +32.13 per thousand in dissolved inorganic carbon (DIC). A mass balance suggested that 43% of the acetate-derived (13)C appeared in DIC and 57% appeared in CH4. Thus, acetate oxidation coupled to sulfate reduction and acetoclastic methanogenesis occurred simultaneously. The delta13C of PLFA increased on average by 27 per thousand in groundwater samples and 4 per thousand in sediment samples. Hence, both suspended and attached communities actively degraded acetate. The PLFA labeling patterns and fluorescent in situ hybridization (FISH) analyses of sediment and groundwater samples suggested that the main sulfate-reducing bacteria degrading the acetate were Desulfotomaculum acetoxidans and Desulfobacter sp. in groundwater, and D. acetoxidans in sediment.     

Transition from anaerobic to aerobic growth conditions for the sulfate-reducing bacterium Desulfovibrio oxyclinae results in flocculation

A chemostat culture of the sulfate-reducing bacterium Desulfovibrio oxyclinae isolated from the oxic layer of a hypersaline cyanobacterial mat was grown anaerobically and then subjected to gassing with 1% oxygen, both at a dilution rate of 0.05 h(-1). The sulfate reduction rate under anaerobic conditions was 370 nmol of SO(4)(2-) mg of protein(-1) min(-1). At the onset of aerobic gassing, sulfate reduction decreased by 40%, although viable cell numbers did not decrease. After 42 h, the sulfate reduction rate returned to the level observed in the anaerobic culture. At this stage the growth yield increased by 180% compared to the anaerobic culture to 4.4 g of protein per mol of sulfate reduced. Protein content per cell increased at the same time by 40%. The oxygen consumption rate per milligram of protein measured in washed cell suspensions increased by 80%, and the thiosulfate reduction rate of the same samples increased by 29% with lactate as the electron donor. These findings indicated possible oxygen-dependent enhancement of growth. After 140 h of growth under oxygen flux, formation of cell aggregates 0.1 to 3 mm in diameter was observed. Micrometer-sized aggregates were found to form earlier, during the first hours of exposure to oxygen. The respiration rate of D. oxyclinae was sufficient to create anoxia inside clumps larger than 3 microm, while the levels of dissolved oxygen in the growth vessel were 0.7 +/- 0.5 microM. Aggregation of sulfate-reducing bacteria was observed within a Microcoleus chthonoplastes-dominated layer of a cyanobacterial mat under daily exposure to oxygen concentrations of up to 900 microM. Desulfonema-like sulfate-reducing bacteria were also common in this environment along with other nonaggregated sulfate-reducing bacteria. Two-dimensional mapping of sulfate reduction showed heterogeneity of sulfate reduction activity in this oxic zone.     

Growth of sulfate-reducing bacteria with solid-phase electron acceptors

Hannebachite (CaSO3 x 0.5H2O), gypsum (CaSO4 x 2H2O), anglesite (PbSO4), and barite (BaSO4) were tested as electron acceptors for sulfate-reducing bacteria with lactate as the electron donor. Hannebachite and gypsum are commonly associated with flue gas desulfurization products, and anglesite is a weathering product found in lead mines. Barite was included as the most insoluble sulfate. Growth of sulfate-reducing bacteria was monitored by protein and sulfide (dissolved H2S and HS-) measurements. Biogenic sulfide formation occurred with all four solid phases, and protein data confirmed that bacteria grew under these electron acceptor conditions. Sulfide formation from gypsum was almost comparable in rate and quantity to that produced from soluble sulfate salt (Na2SO4); hannebachite reduction to sulfide was not as fast. Anglesite as the electron acceptor was also reduced to sulfide in the solution phase and galena (PbS) was detected in solids retrieved from spent cultures. Barite as the electron acceptor supported the least amount of growth and H2S formation. The results demonstrate that low-solubility crystalline phases can be biologically reactive under reducing conditions. Furthermore, the results demonstrate that galena precipitation through sulfide production by sulfate-reducing bacteria serves as a lead enrichment mechanism, thereby also alleviating the potential toxicity of lead. In view of the role of acidophilic thiobacilli in the oxidation of sulfides, the present work accentuates the role of anaerobic and aerobic microbes in the biogeochemical cycling of solid-phase sulfates and sulfides.     

Effects of oxygen exposure on respiratory activities of Desulfovibrio desulfuricans strain DvO1 isolated from activated sludge

The present study addresses the effects of oxygen exposure on the aerobic and anaerobic respiratory activity of Desulfovibrio desulfuricans strain DvO1. This strain was isolated from the highest sulfate-reduction positive most-probable-number dilution (10(6)) of an activated sludge sample, which had been subjected to 120 h of continuous aeration. Washed cell suspensions of strain DvO1 were aerated at 50% atmospheric oxygen saturation in sulfide-free media for a period of 33 h in the presence or absence of an external electron donor (10 mM lactate). During the aeration periods, samples were removed at intervals for determination of anaerobic INT [2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride]-reducing activity, anaerobic sulfate-reducing activity, and oxygen-reducing activity. The cell suspension aerated in the absence of lactate showed negligible endogenous oxygen reduction rates and therefore did not consume oxygen during the aeration period. In contrast, the cell suspension aerated in the presence of lactate sustained significant rates of oxygen reduction during the entire 33 h aeration period. Despite this, no explicit differences in the potential INT-, oxygen-, or sulfate-reducing activities were evident between the two cell suspensions during the aeration periods. Strain DvO1 remained viable throughout the 33 h aeration periods irrespective of the presence or absence of lactate, however, the oxygen exposure resulted in a dose-dependent reversible metabolic inactivation. Notably, lactate-dependent anaerobic sulfate-reducing activity recovered quickly upon anaerobiosis, and was more oxygen tolerant than lactate-dependent oxygen-reducing activity.     

Dechlorination of trichlorofluoromethane (CFC-11) by sulfate-reducing bacteria from an aquifer contaminated with halogenated aliphatic compounds.

Groundwater samples were obtained from a deep aquifer contaminated with halogenated aliphatic compounds. One-milliliter samples contained 9.2 x 10(5) total bacteria (by acridine orange microscopic counts) and 2.5 x 10(3) sulfate-reducing bacteria (by most probable number analysis). Samples were incubated anaerobically in a basal salts medium with acetate as the electron donor and nitrate and sulfate as the electron acceptors. Residual levels of trichlorofluoromethane (CFC-11) in samples were biotically degraded, while trichloroethylene was not. When successively higher levels of CFC-11 were added, increasingly rapid degradation rates were observed. Concomitant with CFC-11 degradation was the near stoichiometric production of fluorodichloromethane (HCFC-21); the production of HCFC-21 was verified by mass spectrometry. CFC-11 degradation was dependent on the presence of acetate (or butyrate) and sulfate but was independent of nitrate. Other carbon sources such as lactate and isopropanol did not support the degradation. The addition of 1 mM sodium sulfide completely inhibited CFC-11 degradation; however, degradation occurred in the presence of 2 mM 2-bromoethanesulfonic acid. These results indicate that the anaerobic dechlorination of CFC-11 is carried out by sulfate-reducing bacteria and not by denitrifying or methanogenic bacteria.     

The dose rate dependence of the relative biological effectiveness of 241Am versus 226Ra gamma rays

The survival of Chinese hamster cells exposed to 59.5 keV 241Am gamma rays was compared with that obtained after exposure to 226Ra gamma rays. The Fricke dosimeter in conjunction with the calculational techniques of transition-zone dosimetry was employed to determine the dose rates to the cells at the petri dish/growth medium interface. The dose rates to the cells ranged from 11 to 133 cGy/h. In all cases, cell survival versus dose was best described by a simple exponential function of dose. For both radiations, graphs of D0 versus dose rate show complex but similar patterns of peaks and valleys. As the curve for 241Am is displaced toward lower dose rates compared with that for 226Ra, the relative biological effectiveness of 241Am vs 226Ra varies considerably with dose rate, ranging from 1.7 at 20 cGy/h to 1.1 at 40 cGy/h to 1.6 at 50 cGy/h. This phenomenon may be due to the LET-dependent accumulation of cells at the G2 + M interface in the cell cycle. The mean unrestricted track-average LET of 241Am (3.7 keV/microns) is 12 times higher than that for 226Ra (0.31 keV/microns) but only one-fifth that of carbon ions (18 keV/microns) for which G2 + M pile-up is observed. Application of the in vitro data derived from this study to the clinical situation, where the dose rate decreases rapidly with distance from the source, suggests that, dose for dose, 241Am will produce results little different from those obtained with 226Ra.     

Distribution of 226Ra body burden of workers in an underground uranium mine in India

Uranium mine workers are exposed to ore dust containing uranium and its daughter products during different mining operations. These radionuclides may pose inhalation hazards to workers during the course of their occupation. The most significant among these radionuclides is ²²⁶Ra. The measurement of radium body burden of uranium mine workers is important to assess their internal exposure. For this purpose, the radon-in-breath measurement technique has been used in the present paper. Workers at the Jaduguda mine, India, associated with different categories of mining operations were monitored between 2001 and 2007. The measurement results indicate that workers—depending on mining operation category—show ²²⁶Ra body burdens ranging from 0.15 to 2.85 kBq. The maximum body burden was found for workers associated with timbering operations, with an average ²²⁶Ra body burden of 0.85 ± 0.54 kBq. Overall, the average value observed for 800 workers was 0.76 ± 0.51 kBq, which gives rise to an average effective dose of 1.67 mSv per year for inhalation and 0.21 mSv per year for ingestion.     

Interaction between methanogenic and sulfate-reducing microorganisms during dechlorination of a high concentration of tetrachloroethylene

A methanogenic and sulfate-reducing consortium, which was enriched on medium containing tetrachloroethylene (PCE), had the ability to dechlorinate high concentrations of PCE. Dehalogenation was due to the direct activity of methanogens. However, interactions between methanogenic and sulfate-reducing bacteria involved modification of the dechlorination process according to culture conditions. In the absence of sulfate, the relative percentage of electrons used in PCE dehalogenation increased after an addition of lactate in batch conditions. The sulfate reducers would produce further reductant from lactate catabolism. This reductant might be used by methanogenic bacteria in PCE dechlorination. A mutualistic interaction was observed in the absence of sulfate. However in the presence of sulfate, methanogenesis and dechlorination decreased because of interspecific competition, probably between the H(2)-oxydizing methanogenic and sulfate-reducing bacteria in batch conditions. In the semicontinuous fixed-bed reactor, the presence of sulfate did not affect dechlorination and methanogenesis. The sulfate-reducing bacteria may not be competitors of H(2)-consuming methanogens in the reactor because of the existence of microbial biofilm. The presence of the fixed film may be an advantage for bioremediation and industrial treatment of effluent charged in sulfate and PCE. This is the first report on the microbial ecology of a methanogenic and sulfate-reducing PCE-enrichment consortium.     

Dissolution of Barium from Barite in Sewage Sludges and Cultures of Desulfovibrio desulfuricans

High concentrations of total barium, ranging from 0.42 to 1.58 mg(middot)g(sup-1) (dry weight) were found in sludges of two sewage treatment plants near Florence, Italy. Barium concentrations in the suspended matter decreased as redox potential values changed from negative to positive. An anoxic sewage sludge sample was aerated, and 30% of the total barium was removed in 24 h. To demonstrate that barium was solubilized from barite by sulfate-reducing bacteria, a strain of Desulfovibrio desulfuricans was used to study the solubilization of barium from barite under laboratory conditions. During cell growth with different concentrations of barite from 0.01 to 0.3 g(middot)liter(sup-1) (the latter is the MIC) as the only source of sulfates in the cultures, the D. desulfuricans strain accumulated barium up to 0.58 (mu)g(middot)mg(sup-1) (dry weight). Three times the quantity of barium was dissolved by bacteria than in the uninoculated medium (control). The unexpectedly low concentration of soluble barium (1.2 mg of Ba(middot)liter(sup-1)) with respect to the quantity expected (109 mg of Ba(middot)liter(sup-1)), calculated on the basis of the free H(inf2)S evolved from the dissimilatory reduction of sulfate from barite, was probably due to the formation of other barium compounds, such as witherite (BaCO(inf3)) and the transient species barium sulfide (BaS). The D. desulfuricans strain, growing on barite, formed visible aggregates. Confocal microscopy analysis showed that aggregates consisted of bacteria and barite. After 3 days of incubation, several autofluorescent crystals surrounded by a dissolution halo were observed. The crystals were identified as BaS by comparison with the commercial compound.     

Anaerobic degradation of volatile fatty acids at different sulphate concentrations

The effect of sulfate on the anaerobic breakdown of mixtures of acetate, propionate and butyrate at three different sulfate to fatty acid ratios was studied in upflow anaerobic sludge blanket reactors. Sludge characteristics were followed with time by means of sludge activity tests and by enumeration of the different physiological bacterial groups. At each sulfate concentration acetate was completely converted into methane and CO₂, and acetotrophic sulfate-reducing bacteria were not detected. Hydrogenotrophic methanogenic bacteria and hydrogenotrophic sulfate-reducing bacteria were present in high numbers in the sludge of all reactors. However, a complete conversion of H₂ by sulfate reducers was found in the reactor operated with excess sulfate. At higher sulfate concentrations, oxidation of propionate by sulfate-reducing bacteria became more important. Only under sulfate-limiting conditions did syntrophic propionate oxidizers out-compete propionate-degrading sulfate reducers. Remarkably, syntrophic butyrate oxidizers were well able to compete with sulfate reducers for the available butyrate, even with an excess of sulfate. Correspondence to: A. Visser     

Untersuchungen zur Wechselwirkung von47Ca,85Sr,133Ba und226Ra mit Proteinen im Rinderserum

Zusammenfassung Mittels Hochdruckultrafiltration wurde im Rinderserum beiin vitro-Markierung mit⁴⁷Ca,⁸⁵Sr,¹³³Ba und²²⁶Ra die Wechselwirkung dieser Elemente mit Proteinen, studiert. Das Ergebnis der Experimente läßt folgende Schlüsse zu: Es besteht zwischen den genannten Erdalkalien und Serumproteinen ein dynamisches, chemisches Gleichgewicht, das unter Berücksichtigung des Aktivitätskoeffizienten durch das Massenwirkungsgesetz beschrieben werden kann. Die Temperatur hat im untersuchten Bereich im Gegensatz zumpH-Wert des Serums keinen großen Einfluß auf das Gleichgewicht; bei Zunahme despH-Wertes, erfolgt eine steigende Bindung der Erdalkalien an Proteine.

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Interaction of⁴⁷Ca,⁸⁵Sr,¹³³Ba and²²⁶Ra with serum proteins

Summary The interaction of Ca, Sr, Ba and Ra with serum proteins was studiedin vitro by means of high presure ultrafiltration of⁴⁷Ca,⁸⁵Sr,¹³³Ba and²²⁶Ra. From these experiments the following conclusions can be drawn: the dynamic equilibrium which exists between these alkaline earth elements and serum protein may be described by the law of mass action considering the activity coefficient. While in the region examined only a moderate influence of temperature on the equilibrium could be observed, the binding of these elements to serum proteins could be considerably increased by increasingpH.

     

Sources and fluxes of submarine groundwater discharge delineated by radium isotopes

This paper reports the results derived fromradium isotopes of a submarine groundwaterdischarge (SGD) intercomparison in thenortheast Gulf of Mexico. Radium isotopesamples were collected from seepage meters,piezometers, and surface and deep ocean waters.Samples collected within the near-shore SGDexperimental area were highly enriched in allfour radium isotopes; offshore samples wereselectively enriched. Samples collected fromseepage meters were about a factor of 2–3higher in radium activity compared to theoverlying waters. Samples from piezometers,which sampled 1–4 meters below the sea bed were1–2 orders of magnitude higher in radiumisotopes than surface waters. The twolong-lived Ra isotopes, ²²⁸Ra and²²⁶Ra, provide convincing evidence thatthere are two sources of SGD to the study area:shallow seepage from the surficial aquifer andinput from a deeper aquifer. A three end-membermixing model can describe the Ra distributionin these samples. The short-lived radium isotopes, ²²³Ra and²²⁴Ra, were used to establish mixing ratesfor the near-shore study area. Mixing wasretarded within 3 km of shore due to a strongsalinity gradient. The product of the mixingrate and the offshore ²²⁶Ra gradientestablished the ²²⁶Ra flux. This flux mustbe balanced by Ra input from SGD. The flux ofSGD within 200 m of shore based on the²²⁶Ra budget was 1.5 m³ min^?1.This flux agreed well with other estimatesbased on seepage meters and ²²²Rn.     

Activity and diversity of sulfate-reducing bacteria in a petroleum hydrocarbon-contaminated aquifer

Microbial sulfate reduction is an important metabolic activity in petroleum hydrocarbon (PHC)-contaminated aquifers. We quantified carbon source-enhanced microbial SO(4)(2-) reduction in a PHC-contaminated aquifer by using single-well push-pull tests and related the consumption of sulfate and added carbon sources to the presence of certain genera of sulfate-reducing bacteria (SRB). We also used molecular methods to assess suspended SRB diversity. In four consecutive tests, we injected anoxic test solutions (1,000 liters) containing bromide as a conservative tracer, sulfate, and either propionate, butyrate, lactate, or acetate as reactants into an existing monitoring well. After an initial incubation period, 1,000 liters of test solution-groundwater mixture was extracted from the same well. Average total test duration was 71 h. We measured concentrations of bromide, sulfate, and carbon sources in native groundwater as well as in injection and extraction phase samples and characterized the SRB population by using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE). Enhanced sulfate reduction concomitant with carbon source degradation was observed in all tests. Computed first-order rate coefficients ranged from 0.19 to 0.32 day(-1) for sulfate reduction and from 0.13 to 0.60 day(-1) for carbon source degradation. Sulfur isotope fractionation in unconsumed sulfate indicated that sulfate reduction was microbially mediated. Enhancement of sulfate reduction due to carbon source additions in all tests and variability of rate coefficients suggested the presence of specific SRB genera and a high diversity of SRB. We confirmed this by using FISH and DGGE. A large fraction of suspended bacteria hybridized with SRB-targeting probes SRB385 plus SRB385-Db (11 to 24% of total cells). FISH results showed that the activity of these bacteria was enhanced by addition of sulfate and carbon sources during push-pull tests. However, DGGE profiles indicated that the bacterial community structure of the dominant species did not change during the tests. Thus, the combination of push-pull tests with molecular methods provided valuable insights into microbial processes, activities, and diversity in the sulfate-reducing zone of a PHC-contaminated aquifer.     

Aerobic Organic Carbon Mineralization by Sulfate-Reducing Bacteria in the Oxygen-Saturated Photic Zone of a Hypersaline Microbial Mat

The sulfate-reducing bacterium strain SRB D2 isolated from the photic zone of a hypersaline microbial mat, from Lake Chiprana, NE Spain, respired pyruvate, alanine, and α-ketoglutarate but not formate, lactate, malate, succinate, and serine at significant rates under fully oxic conditions. Dehydrogenase enzymes of only the former substrates are likely oxygen-tolerant as all substrates supported anaerobic sulfate reduction. No indications were found, however, that aerobic respiration supported growth. Although strain SRB D2 appeared phylogenetically closely related to the oxygen-tolerant sulfate-reducing bacterium Desulfovibrio oxyclinae, substrate spectra were markedly different. Most-probable-number (MPN) estimates of sulfate-reducing bacteria and aerobic heterotrophic bacteria indicated that the latter were numerically dominant in both the photic and aphotic zones of the mat. Moreover, substrate spectra of representative isolates showed that the aerobic heterotrophic bacteria are metabolically more diverse. These findings indicate that sulfate-reducing bacteria in the fully oxic photic zone of mats have to compete with aerobic heterotrophic bacteria for organic substrates. Porewater analysis revealed that total carbohydrates and low-molecular-weight carbon compounds (LMWC) made up substantial fractions of the total dissolved organic carbon (DOC) pool and that nighttime degradation of the former was concomitant with increased concentration of the latter. Our findings indicate that aerobic respiration by sulfate-reducing bacteria contributes to organic carbon mineralization in the oxic zone of microbial mats as daytime porewater LMWC concentrations are above typical half-saturation constants.     

Sulfate-reducing bacteria in gypsum karst lakes of northern Lithuania

Microbiological studies were performed in three small gypsum karst lakes in northern Lithuania, most typical of the region. Samples were taken in different seasons of 2001. The conditions for microbial growth in the lakes are determined by elevated content of salts (from 0.5 to 2.0 g/l), dominated by SO(2-)4 and Ca2+ ions (up to 1.4 and 0.6 g/l, respectively). The elevated sulfate concentration is favorable for sulfate-reducing bacteria (SRBs). Summer and winter stratification gives rise to anaerobic water layers enriched in products of anaerobic degradation: H2S and CH4. The lakes under study contain abundant SRBs not only in bottom sediments (from 10(3) to 10(7) cells/dm3) but also in the water column (from 10(2) to 10(6) cells/ml). The characteristic spatial and temporal variations in the rate of sulfate reduction were noted. The highest rates of this process were recorded in summer: 0.95-2.60 mg S(2-)/dm3 per day in bottom sediments and up to 0.49 mg S(2-)/l per day in the water column. The maximum values (up to 11.36 mg S(2-)/dm3) were noted in areas where bottom sediments were enriched in plankton debris. Molecular analysis of conservative sequences of the gene for 16S RNA in sulfate-reducing microorganisms grown on lactate allowed them to be identified as Desulfovibrio desulfuricans.     

Sulfate reduction from phosphogypsum using a mixed culture of sulfate-reducing bacteria

Phosphogypsum (CaSO₄), a primary by-product of phosphoric acid production, is accumulated in large stockpiles and occupies vast areas of land. It poses a severe threat to the quality of water and land in countries producing phosphoric acid. In this study, the potential of sulfate-reducing bacteria for biodegradation of this sulfur-rich industrial solid waste was assessed. The effect of phosphogypsum concentration, carbon and nitrogen sources, temperature, pH and stirring on the growth of sulfate-reducing bacteria was investigated. Growth of sulfate-reducing bacteria was monitored by measuring sulfide production. Phosphogypsum was shown to be a good source of sulfate, albeit that the addition of organic carbon was necessary for bacterial growth. Biogenic sulfide production occurred with phosphogypsum up to a concentration of 40 g L⁻¹, above which no growth of sulfate-reducing bacteria was observed. Optimal growth was obtained at 10 g L⁻¹ phosphogypsum. Both the gas mixture H₂/CO₂ and lactate supported high amounts of H₂S formation (19 and 11 mM, respectively). The best source of nitrogen for sulfate-reducing bacteria was yeast extract, followed by ammonium chloride. The presence of nitrate had an inhibitory effect on the process of sulfate reduction. Stirring the culture at 150 rpm slightly stimulated H₂S formation, probably by improving sulfate solubility.     

Novel thermophilic sulfate-reducing bacteria from a geothermally active underground mine in Japan

Thermophilic sulfate-reducing bacteria were enriched from samples obtained from a geothermal underground mine in Japan. The enrichment cultures contained bacteria affiliated with the genera Desulfotomaculum, Thermanaeromonas, Thermincola, Thermovenabulum, Moorella, "Natronoanaerobium," and Clostridium. Two novel thermophilic sulfate-reducing strains, RL50JIII and RL80JIV, affiliated with the genera Desulfotomaculum and Thermanaeromonas, respectively, were isolated.     

Isolation, characterization, and in situ detection of a novel chemolithoautotrophic sulfur-oxidizing bacterium in wastewater biofilms growing under microaerophilic conditions

We successfully isolated a novel aerobic chemolithotrophic sulfur-oxidizing bacterium, designated strain SO07, from wastewater biofilms growing under microaerophilic conditions. For isolation, the use of elemental sulfur (S(0)), which is the most abundant sulfur pool in the wastewater biofilms, as the electron donor was an effective measure to establish an enrichment culture of strain SO07 and further isolation. 16S rRNA gene sequence analysis revealed that newly isolated strain SO07 was affiliated with members of the genus Halothiobacillus, but it was only distantly related to previously isolated species (89% identity). Strain SO07 oxidized elemental sulfur, thiosulfate, and sulfide to sulfate under oxic conditions. Strain SO07 could not grow on nitrate. Organic carbons, including acetate, propionate, and formate, could not serve as carbon and energy sources. Unlike other aerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 150 mM was negligible. In situ hybridization combined with confocal laser scanning microscopy revealed that a number of rod-shaped cells hybridized with a probe specific for strain SO07 were mainly present in the oxic biofilm strata (ca. 0 to 100 micro m) and that they often coexisted with sulfate-reducing bacteria in this zone. These results demonstrated that strain SO07 was one of the important sulfur-oxidizing populations involved in the sulfur cycle occurring in the wastewater biofilm and was primarily responsible for the oxidation of H(2)S and S(0) to SO(4)(2-) under oxic conditions.