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1.
Interstitial water profiles of SeO 42−, SeO 32−, SO 42−, and Cl − in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO 42− occurred under anaerobic conditions, was more rapid with H 2 or acetate, and was inhibited by O 2, NO 3−, MnO 2, or autoclaving but not by SO 42− or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO 2. A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters. 相似文献
2.
Cultures of a purple nonsulfur bacterium, Rhodobacter sphaeroides, amended with ~1 or ~100 ppm selenate or selenite, were grown phototrophically to stationary phase. Analyses of culture headspace, separated cells, and filtered culture supernatant were carried out using gas chromatography, X-ray absorption spectroscopy, and inductively coupled plasma spectroscopy-mass spectrometry, respectively. While selenium-amended cultures showed much higher amounts of SeO 32− bioconversion than did analogous selenate experiments (94% uptake for SeO 32− as compared to 9.6% for SeO 42−-amended cultures from 100-ppm solutions), the chemical forms of selenium in the microbial cells were not very different except at exposure to high concentrations of selenite. Volatilization accounted for only a very small portion of the accumulated selenium; most was present in organic forms and the red elemental form. 相似文献
3.
Dissimilatory in situ selenate reduction to elemental selenium in sediments from irrigated agricultural drainage regions of western Nevada was measured at ambient Se oxyanion concentrations. Selenate reduction was rapid, with turnover rate constants ranging from 0.04 to 1.8 h-1 at total Se concentrations in pore water of 13 to 455 nM. Estimates of removal rates of selenium oxyanions were 14.38, and 155 mumol m-2 day-1 for South Lead Lake, Massie Slough, and Hunter Drain, respectively. 相似文献
4.
Dissimilatory in situ selenate reduction to elemental selenium in sediments from irrigated agricultural drainage regions of western Nevada was measured at ambient Se oxyanion concentrations. Selenate reduction was rapid, with turnover rate constants ranging from 0.04 to 1.8 h-1 at total Se concentrations in pore water of 13 to 455 nM. Estimates of removal rates of selenium oxyanions were 14.38, and 155 mumol m-2 day-1 for South Lead Lake, Massie Slough, and Hunter Drain, respectively. 相似文献
5.
The prokaryotic community composition and diversity and the distribution patterns at various taxonomic levels across gradients of salinity and physiochemical properties in the surface waters of seven plateau lakes in the Qaidam Basin, Tibetan Plateau, were evaluated using Illumina MiSeq sequencing. These lakes included Lakes Keluke (salinity, <1 g/liter), Qing (salinity, 5.5 to 6.6 g/liter), Tuosu (salinity, 24 to 35 g/liter), Dasugan (salinity, 30 to 33 g/liter), Gahai (salinity, 92 to 96 g/liter), Xiaochaidan (salinity, 94 to 99 g/liter), and Gasikule (salinity, 317 to 344 g/liter). The communities were dominated by Bacteria in lakes with salinities of <100 g/liter and by Archaea in Lake Gasikule. The clades At12OctB3 and Salinibacter, previously reported only in hypersaline environments, were found in a hyposaline lake (salinity, 5.5 to 6.6 g/liter) at an abundance of ∼1.0%, indicating their ecological plasticity. Salinity and the concentrations of the chemical ions whose concentrations covary with salinity (Mg 2+, K +, Cl −, Na +, SO 42−, and Ca 2+) were found to be the primary environmental factors that directly or indirectly determined the composition and diversity at the level of individual clades as well as entire prokaryotic communities. The distribution patterns of two phyla, five classes, five orders, five families, and three genera were well predicted by salinity. The variation of the prokaryotic community structure also significantly correlated with the dissolved oxygen concentration, pH, the total nitrogen concentration, and the PO 43− concentration. Such correlations varied depending on the taxonomic level, demonstrating the importance of comprehensive correlation analyses at various taxonomic levels in evaluating the effects of environmental variable factors on prokaryotic community structures. Our findings clarify the distribution patterns of the prokaryotic community composition in plateau lakes at the levels of individual clades as well as whole communities along gradients of salinity and ionic concentrations. 相似文献
6.
Enterobacter cloacae SLD1a-1 is capable of reductive detoxification of selenate to elemental selenium under aerobic growth conditions. The initial reductive step is the two-electron reduction of selenate to selenite and is catalyzed by a molybdenum-dependent enzyme demonstrated previously to be located in the cytoplasmic membrane, with its active site facing the periplasmic compartment (C. A. Watts, H. Ridley, K. L. Condie, J. T. Leaver, D. J. Richardson, and C. S. Butler, FEMS Microbiol. Lett. 228:273-279, 2003). This study describes the purification of two distinct membrane-bound enzymes that reduce either nitrate or selenate oxyanions. The nitrate reductase is typical of the NAR-type family, with α and β subunits of 140 kDa and 58 kDa, respectively. It is expressed predominantly under anaerobic conditions in the presence of nitrate, and while it readily reduces chlorate, it displays no selenate reductase activity in vitro. The selenate reductase is expressed under aerobic conditions and expressed poorly during anaerobic growth on nitrate. The enzyme is a heterotrimeric (αβγ) complex with an apparent molecular mass of ~600 kDa. The individual subunit sizes are ~100 kDa (α), ~55 kDa (β), and ~36 kDa (γ), with a predicted overall subunit composition of α 3β 3γ 3. The selenate reductase contains molybdenum, heme, and nonheme iron as prosthetic constituents. Electronic absorption spectroscopy reveals the presence of a b-type cytochrome in the active complex. The apparent Km for selenate was determined to be ~2 mM, with an observed Vmax of 500 nmol SeO 42− min −1 mg −1 ( kcat, ~5.0 s −1). The enzyme also displays activity towards chlorate and bromate but has no nitrate reductase activity. These studies report the first purification and characterization of a membrane-bound selenate reductase. 相似文献
7.
A radioisotope method was devised to study bacterial respiratory reduction of arsenate in sediments. The following two arsenic-rich soda lakes in California were chosen for comparison on the basis of their different salinities: Mono Lake (~90 g/liter) and Searles Lake (~340 g/liter). Profiles of arsenate reduction and sulfate reduction were constructed for both lakes. Reduction of [ 73As]arsenate occurred at all depth intervals in the cores from Mono Lake (rate constant [ k] = 0.103 to 0.04 h −1) and Searles Lake ( k = 0.012 to 0.002 h −1), and the highest activities occurred in the top sections of each core. In contrast, [ 35S]sulfate reduction was measurable in Mono Lake ( k = 7.6 ×10 4 to 3.2 × 10 −6 h −1) but not in Searles Lake. Sediment DNA was extracted, PCR amplified, and separated by denaturing gradient gel electrophoresis (DGGE) to obtain phylogenetic markers (i.e., 16S rRNA genes) and a partial functional gene for dissimilatory arsenate reduction ( arrA). The amplified arrA gene product showed a similar trend in both lakes; the signal was strongest in surface sediments and decreased to undetectable levels deeper in the sediments. More arrA gene signal was observed in Mono Lake and was detectable at a greater depth, despite the higher arsenate reduction activity observed in Searles Lake. A partial sequence (about 900 bp) was obtained for a clone (SLAS-3) that matched the dominant DGGE band found in deeper parts of the Searles Lake sample (below 3 cm), and this clone was found to be closely related to SLAS-1, a novel extremophilic arsenate respirer previously cultivated from Searles Lake. 相似文献
8.
The trace metal selenium is in demand for health supplements to human and animal nutrition. We studied the reduction of selenite (SeO 3
−2) to red elemental selenium by Rhodopseudomonas palustris strain N. This strain was cultured in a medium containing SeO 3
−2 and the particles obtained from cultures were analyzed using transmission electron microscopy (TEM), energy dispersive microanalysis (EDX) and X ray diffraction analysis (XRD). Our results showed the strain N could reduce SeO 3
−2 to red elemental selenium. The diameters of particles were 80–200 nm. The bacteria exhibited significant tolerance to SeO 3
−2 up to 8.0 m mol/L concentration with an EC 50 value of 2.4 m mol/L. After 9 d of cultivation, the presence of SeO 3
2− up to 1.0 m mol/L resulted in 99.9% reduction of selenite, whereas 82.0% (p<0.05), 31.7% (p<0.05) and 2.4% (p<0.05) reduction of SeO 3
−2 was observed at 2.0, 4.0 and 8.0 m mol/L SeO 3
2− concentrations, respectively. This study indicated that red elemental selenium was synthesized by green technology using Rhodopseudomonas palustris strain N. This strain also indicated a high tolerance to SeO 3
−2. The finding of this work will contribute to the application of selenium to human health. 相似文献
9.
Experiments demonstrated that Beggiatoa could induce a H 2S-depleted suboxic zone of more than 10 mm in marine sediments and cause a divergence in sediment NO 3− reduction from denitrification to dissimilatory NO 3− reduction to ammonium. pH, O 2, and H 2S profiles indicated that the bacteria oxidized H 2S with NO 3− and transported S 0 to the sediment surface for aerobic oxidation. 相似文献
10.
Active transport of SO 42− and SeO 42− has been evaluated during 60-hour contact of barley roots with nutrient solutions containing either 35SO 42− or 75SeO 42−, or both ions, at 0.1 milli-equivalent per liter. In the SO 42− solution the time course of active transport follows a straight line; if SeO 42− is also present transport is strongly inhibited after 20 to 30 hours for both ions. The S-Se uptake ratio remains 1.4 during the 60 hours; S-Se ratio shifts from 3.0 to 3.3 in proteins and falls to 0.6 in free amino acids. S-Se discrimination is mainly operating at the level of amino acid incorporation into proteins. The presence of Se-amino acids blocks this incorporation and brings about an accumulation of free amino acids; at the same time carrier activity is inhibited. The addition of methionine or Se-methionine causes a 60 to 80% inhibition of the active transport. 相似文献
11.
Mining-impacted sediments of Lake Coeur d'Alene, Idaho, contain more than 10% metals on a dry weight basis, approximately 80% of which is iron. Since iron (hydr)oxides adsorb toxic, ore-associated elements, such as arsenic, iron (hydr)oxide reduction may in part control the mobility and bioavailability of these elements. Geochemical and microbiological data were collected to examine the ecological role of dissimilatory Fe(III)-reducing bacteria in this habitat. The concentration of mild-acid-extractable Fe(II) increased with sediment depth up to 50 g kg −1, suggesting that iron reduction has occurred recently. The maximum concentrations of dissolved Fe(II) in interstitial water (41 mg liter −1) occurred 10 to 15 cm beneath the sediment-water interface, suggesting that sulfidogenesis may not be the predominant terminal electron-accepting process in this environment and that dissolved Fe(II) arises from biological reductive dissolution of iron (hydr)oxides. The concentration of sedimentary magnetite (Fe 3O 4), a common product of bacterial Fe(III) hydroxide reduction, was as much as 15.5 g kg −1. Most-probable-number enrichment cultures revealed that the mean density of Fe(III)-reducing bacteria was 8.3 × 10 5 cells g (dry weight) of sediment −1. Two new strains of dissimilatory Fe(III)-reducing bacteria were isolated from surface sediments. Collectively, the results of this study support the hypothesis that dissimilatory reduction of iron has been and continues to be an important biogeochemical process in the environment examined. 相似文献
12.
A perfusion method for assaying nitrogenase activity (acetylene reduction) in marine sediments was developed. The method was used to assay sediment cores from Spartina alterniflora (salt marsh), Zostera marina (sea grass), and Thalassia testudinum (sea grass) communities, and the results were compared with those of conventional sealed-flask assays. Rates of ethylene production increased progressively with time in the perfusion assays, reaching plateau values of 2 to 3 nmol · g of dry sediment −1 · h −1 by 10 to 20 h. Depletion of interstitial NH 4+ was implicated in this stimulation of nitrogenase activity. Initial acetylene reduction rates determined by the perfusion assay of cores from the Spartina community ranged from 0.15 to 0.60 nmol of C 2H 4 · g of dry sediment −1 · h −1. These rates were similar to those for sediments assayed in sealed flasks without seawater when determined over linear periods of C 2H 4 production. Initial values obtained by using the perfusion method were 0.66 nmol of C 2H 4 · g of dry sediment −1 · h −1 for sediments from Zostera communities and 0.70 nmol of C 2H 4 · g of dry sediment −1 · h −1 for sediments from Thalassia communities. In all cases, rates determined by simultaneous slurry assays were lower than those determined by the perfusion method. 相似文献
13.
Concentrations of various sulfur compounds (SO 42−, H 2S, S 0, acid-volatile sulfide, and total sulfur) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of sulfate relative to those of acid-volatile sulfide and total sulfur and a decrease in total sulfur with sediment depth implied that the contribution of dissimilatory sulfur reduction to H 2S production was relatively minor. Addition of 1.0 mM Na 235SO 4 to upper sediments in laboratory experiments resulted in the production of H 235S with no apparent lag. Kinetic experiments with 35S demonstrated an apparent Km of 0.068 mmol of SO 42− reduced per liter of sediment per day, whereas tracer experiments with 35S indicated an average turnover time of the sediment sulfate pool of 1.5 h. Total sulfate reduction in a sediment depth profile to 15 cm was 15.3 mmol of sulfate reduced per m 2 per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of 35S 0 occurred at a slower rate. These results demonstrated that high rates of sulfate reduction occur in these sediments despite low concentrations of oxidized inorganic compounds and that this reduction can be important in the anaerobic mineralization of organic carbon. 相似文献
14.
The capacity for dissimilatory reduction of NO 3− to N 2 (N 2O) and NH 4+ was measured in 15NO 3−-amended marine sediment. Incubation with acetylene (7 × 10 −3 atmospheres [normal]) caused accumulation of N 2O in the sediment. The rate of N 2O production equaled the rate of N 2 production in samples without acetylene. Complete inhibition of the reduction of N 2O to N 2 suggests that the “acetylene blockage technique” is applicable to assays for denitrification in marine sediments. The capacity for reduction of NO 3− by denitrification decreased rapidly with depth in the sediment, whereas the capacity for reduction of NO 3− to NH 4+ was significant also in deeper layers. The data suggested that the latter process may be equally as significant as denitrification in the turnover of NO 3− in marine sediments. 相似文献
15.
Nitrogenase activity in mangrove forests at two locations in the North Island, New Zealand, was measured by acetylene reduction and 15N 2 uptake. Nitrogenase activity (C 2H 2 reduction) in surface sediments 0 to 10 mm deep was highly correlated ( r = 0.91, n = 17) with the dry weight of decomposing particulate organic matter in the sediment and was independent of light. The activity was not correlated with the dry weight of roots in the top 10 mm of sediment ( r = −0.01, n = 13). Seasonal and sample variation in acetylene reduction rates ranged from 0.4 to 50.0 μmol of C 2H 4 m −2 h −1 under air, and acetylene reduction was depressed in anaerobic atmospheres. Nitrogen fixation rates of decomposing leaves from the surface measured by 15N 2 uptake ranged from 5.1 to 7.8 nmol of N 2 g (dry weight) −1 h −1, and the mean molar ratio of acetylene reduced to nitrogen fixed was 4.5:1. Anaerobic conditions depressed the nitrogenase activity in decomposing leaves, which was independent of light. Nitrogenase activity was also found to be associated with pneumatophores. This activity was light dependent and was probably attributable to one or more species of Calothrix present as an epiphyte. Rates of activity were generally between 100 and 500 nmol of C 2H 4 pneumatophore −1 h −1 in summer, but values up to 1,500 nmol of C 2H 4 pneumatophore −1 h −1 were obtained. 相似文献
16.
Addition of nickel stimulated growth and nitrogenase activity of Pseudomonas saccharophila under nitrogen-limited chemolithotrophic conditions, apparently because of a significant increase in expression of uptake hydrogenase activity. Inhibition of hydrogenase expression by 50 μM EDTA was relieved by nickel over a wide concentration range (1 to 200 μM). Co 2+, Zn 2+, Mn 2+, and Cu 2+ stimulated expression of hydrogenase activity, but to a much lesser degree than nickel, and Fe 2+, Mg 2+, SeO 42−, and SeO 32− did not increase expression. Nickel in individual combination with Mg 2+, Fe 2+, SeO 32−, and SeO 42− resulted in activities that were essentially the same as that with nickel alone. Hydrogenase synthesis required the presence of nickel, and repression by O 2 was alleviated by increasing the concentration of added nickel. Cells placed under hydrogenase derepression conditions showed progressive incorporation of radioactive nickel to a much greater extent than did cells which were not derepressed. 相似文献
17.
The contribution of the biochemical pathways nitrification, denitrification, and dissimilatory NO 3− reduction to NH 4+ (DNRA) to the accumulation of NO 2− in freshwaters is governed by the species compositions of the bacterial populations resident in the sediments, available carbon (C) and nitrogen (N) substrates, and environmental conditions. Recent studies of major rivers in Northern Ireland have shown that high NO 2− concentrations found in summer, under warm, slow-flowing conditions, arise from anaerobic NO 3− reduction. Locally, agricultural pollutants entering rivers are important C and N sources, providing ideal substrates for the aquatic bacteria involved in cycling of N. In this study a range of organic C compounds commonly found in agricultural pollutants were provided as energy sources in 48-h incubation experiments to investigate if the chemical compositions of the pollutants affected which NO 3− reduction pathway was followed and influenced subsequent NO 2− accumulation. Carbon stored within the sediments was sufficient to support DNRA and denitrifier populations, and the resulting NO 2− peak (80 μg of N liter −1 [approximate]) observed at 24 h was indicative of the simultaneous activities of both bacterial groups. The value of glycine as an energy source for denitrification or DNRA appeared to be limited, but glycine was an important source of additional N. Glucose was an efficient substrate for both the denitrification and DNRA pathways, with a NO 2− peak of 160 μg of N liter −1 noted at 24 h. Addition of formate and acetate stimulated continuous NO 2− production throughout the 48-h period, caused by partial inhibition of the denitrification pathway. The formate treatment resulted in a high NO 2− accumulation (1,300 μg of N liter −1 [approximate]), and acetate treatment resulted in a low NO 2− concentration (<100 μg of N liter −1). 相似文献
18.
The effect of NaCl and Na 2SO 4 salinity on NO 3− assimilation in young barley ( Hordeum vulgare L. var Numar) seedlings was studied. The induction of the NO 3− transporter was affected very little; the major effect of the salts was on its activity. Both Cl − and SO 42− salts severely inhibited uptake of NO 3−. When compared on the basis of osmolality of the uptake solutions, Cl − salts were more inhibitory (15-30%) than SO 42− salts. At equal concentrations, SO 42− salts inhibited NO 3− uptake 30 to 40% more than did Cl − salts. The absolute concentrations of each ion seemed more important as inhibitors of NO 3− uptake than did the osmolality of the uptake solutions. Both K + and Na + salts inhibited NO 3− uptake similarly; hence, the process seemed more sensitive to anionic salinity than to cationic salinity. Unlike NO3− uptake, NO3− reduction was not affected by salinity in short-term studies (12 hours). The rate of reduction of endogenous NO3− in leaves of seedlings grown on NaCl for 8 days decreased only 25%. Nitrate reductase activity in the salt-treated leaves also decreased 20% but its activity, determined either in vitro or by the `anaerobic' in vivo assay, was always greater than the actual in situ rate of NO3− reduction. When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in situ nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO3− transporter, rather than that of the NO3− reduction system, may be a critical factor to plant survival during salt stress. 相似文献
19.
The absorption characteristics and mechanisms of pertechnetate (TcO 4−) uptake by hydroponically grown soybean seedlings ( Glycine max cv Williams) were determined. Absorption from 10 micromolar solutions was linear for at least 6 hours, with 30% of the absorbed TcO 4− being transferred to the shoot. Evaluation of concentration-dependent absorption rates from solutions containing 0.02 to 10 micromolar TcO 4− shows the presence of multiphasic absorption isotherms with calculated K s values of 0.09, 8.9, and 54 micromolar for intact seedlings. The uptake of TcO 4− was inhibited by a 4-fold concentration excess of sulfate, phosphate, selenate, molybdate, and permanganate; no reduction was noted with borate, nitrate, tungstate, perrhenate, iodate, or vanadate. Analyses of the kinetics of interaction between TcO 4− and inhibiting anions show permanganate to be a noncompetitive inhibitor, while sulfate, phosphate, and selenate, and molybdate exhibit characteristics of competitive inhibitors of TcO 4− transport suggesting involvement of a common transport process. 相似文献
20.
Aerobic and anaerobic groundwater continuous-flow microcosms were designed to study nitrate reduction by the indigenous bacteria in intact saturated soil cores from a sandy aquifer with a concentration of 3.8 mg of NO 3−-N liter −1. Traces of 15NO 3− were added to filter-sterilized groundwater by using a Darcy flux of 4 cm day −1. Both assimilatory and dissimilatory reduction rates were estimated from analyses of 15N 2, 15N 2O, 15NH 4+, and 15N-labeled protein amino acids by capillary gas chromatography-mass spectrometry. N 2 and N 2O were separated on a megabore fused-silica column and quantified by electron impact-selected ion monitoring. NO 3− and NH 4+ were analyzed as pentafluorobenzoyl amides by multiple-ion monitoring and protein amino acids as their N-heptafluorobutyryl isobutyl ester derivatives by negative ion-chemical ionization. The numbers of bacteria and their [ methyl- 3H]thymidine incorporation rates were simultaneously measured. Nitrate was completely reduced in the microcosms at a rate of about 250 ng g −1 day −1. Of this nitrate, 80 to 90% was converted by aerobic denitrification to N 2, whereas only 35% was denitrified in the anaerobic microcosm, where more than 50% of NO 3− was reduced to NH 4+. Assimilatory reduction was recorded only in the aerobic microcosm, where N appeared in alanine in the cells. The nitrate reduction rates estimated for the aquifer material were low in comparison with rates in eutrophic lakes and coastal sediments but sufficiently high to remove nitrate from an uncontaminated aquifer of the kind examined in less than 1 month. 相似文献
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