共查询到20条相似文献,搜索用时 484 毫秒
1.
Capacity for Denitrification and Reduction of Nitrate to Ammonia in a Coastal Marine Sediment 总被引:37,自引:23,他引:14 下载免费PDF全文
Jan Srensen 《Applied microbiology》1978,35(2):301-305
The capacity for dissimilatory reduction of NO3− to N2 (N2O) and NH4+ was measured in 15NO3−-amended marine sediment. Incubation with acetylene (7 × 10−3 atmospheres [normal]) caused accumulation of N2O in the sediment. The rate of N2O production equaled the rate of N2 production in samples without acetylene. Complete inhibition of the reduction of N2O to N2 suggests that the “acetylene blockage technique” is applicable to assays for denitrification in marine sediments. The capacity for reduction of NO3− by denitrification decreased rapidly with depth in the sediment, whereas the capacity for reduction of NO3− to NH4+ was significant also in deeper layers. The data suggested that the latter process may be equally as significant as denitrification in the turnover of NO3− in marine sediments. 相似文献
2.
Anaerobic Ammonium Oxidation Measured in Sediments along the Thames Estuary, United Kingdom 总被引:7,自引:3,他引:4 下载免费PDF全文
Until recently, denitrification was thought to be the only significant pathway for N2 formation and, in turn, the removal of nitrogen in aquatic sediments. The discovery of anaerobic ammonium oxidation in the laboratory suggested that alternative metabolisms might be present in the environment. By using a combination of 15N-labeled NH4+, NO3−, and NO2− (and 14N analogues), production of 29N2 and 30N2 was measured in anaerobic sediment slurries from six sites along the Thames estuary. The production of 29N2 in the presence of 15NH4+ and either 14NO3− or 14NO2− confirmed the presence of anaerobic ammonium oxidation, with the stoichiometry of the reaction indicating that the oxidation was coupled to the reduction of NO2−. Anaerobic ammonium oxidation proceeded at equal rates via either the direct reduction of NO2− or indirect reduction, following the initial reduction of NO3−. Whether NO2− was directly present at 800 μM or it accumulated at 3 to 20 μM (from the reduction of NO3−), the rate of 29N2 formation was not affected, which suggested that anaerobic ammonium oxidation was saturated at low concentrations of NO2−. We observed a shift in the significance of anaerobic ammonium oxidation to N2 formation relative to denitrification, from 8% near the head of the estuary to less than 1% at the coast. The relative importance of anaerobic ammonium oxidation was positively correlated (P < 0.05) with sediment organic content. This report of anaerobic ammonium oxidation in organically enriched estuarine sediments, though in contrast to a recent report on continental shelf sediments, confirms the presence of this novel metabolism in another aquatic sediment system. 相似文献
3.
Denitrification and Assimilatory Nitrate Reduction in Aquaspirillum magnetotacticum 总被引:7,自引:5,他引:2 下载免费PDF全文
Aquaspirillum magnetotacticum MS-1 grew microaerobically but not anaerobically with NO3− or NH4+ as the sole nitrogen source. Nevertheless, cell yields varied directly with NO3− concentration under microaerobic conditions. Products of NO3− reduction included NH4+, N2O, NO, and N2. NO2− and NH2OH, each toxic to cells at 0.2 mM, were not detected as products of cells growing on NO3−. NO3− reduction to NH4+ was completely repressed by the addition of 2 mM NH4+ to the growth medium, whereas NO3− reduction to N2O or to N2 was not. C2H2 completely inhibited N2O reduction to N2 by growing cells. These results indicate that A. magnetotacticum is a microaerophilic denitrifier that is versatile in its nitrogen metabolism, concomitantly reducing NO3− by assimilatory and dissimilatory means. This bacterium appears to be the first described denitrifier with an absolute requirement for O2. The process of NO3− reduction appears well adapted for avoiding accumulation of several nitrogenous intermediates that are toxic to cells. 相似文献
4.
A recent study (D. C. Cooper, F. W. Picardal, A. Schimmelmann, and A. J. Coby, Appl. Environ. Microbiol. 69:3517-3525, 2003) has shown that NO3− and NO2− (NOx−) reduction by Shewanella putrefaciens 200 is inhibited in the presence of goethite. The hypothetical mechanism offered to explain this finding involved the formation of a Fe(III) (hydr)oxide coating on the cell via the surface-catalyzed, abiotic reaction between Fe2+ and NO2−. This coating could then inhibit reduction of NOx− by physically blocking transport into the cell. Although the data in the previous study were consistent with such an explanation, the hypothesis was largely speculative. In the current work, this hypothesis was tested and its environmental significance explored through a number of experiments. The inhibition of ~3 mM NO3− reduction was observed during reduction of a variety of Fe(III) (hydr)oxides, including goethite, hematite, and an iron-bearing, natural sediment. Inhibition of oxygen and fumarate reduction was observed following treatment of cells with Fe2+ and NO2−, demonstrating that utilization of other soluble electron acceptors could also be inhibited. Previous adsorption of Fe2+ onto Paracoccus denitrificans inhibited NOx− reduction, showing that Fe(II) can reduce rates of soluble electron acceptor utilization by non-iron-reducing bacteria. NO2− was chemically reduced to N2O by goethite or cell-sorbed Fe2+, but not at appreciable rates by aqueous Fe2+. Transmission and scanning electron microscopy showed an electron-dense, Fe-enriched coating on cells treated with Fe2+ and NO2−. The formation and effects of such coatings underscore the complexity of the biogeochemical reactions that occur in the subsurface. 相似文献
5.
Ronald S. Oremland Cindy Umberger Charles W. Culbertson Richard L. Smith 《Applied microbiology》1984,47(5):1106-1112
The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO3− + NO2− concentrations (≤26 μM) were below the apparent Km (50 μM) for nitrate. During the rainy season, when ambient NO3− + NO2− concentrations were higher (37 to 89 μM), an accurate estimate of the Km could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N2O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N2O in the presence of C2H2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N2O loss was caused by incomplete blockage of N2O reductase by C2H2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N2 m−2 h−1 (for undisturbed sediments) to 17 to 280 μmol of N2 m−2 h−1 (for shaken sediment slurries). 相似文献
6.
Annual Pattern of Denitrification and Nitrate Ammonification in Estuarine Sediment 总被引:11,自引:2,他引:9 下载免费PDF全文
Kirsten Schannong Jrgensen 《Applied microbiology》1989,55(7):1841-1847
The seasonal variation and depth distribution of the capacity for denitrification and dissimilatory NO3− reduction to NH4+ (NO3− ammonification) were studied in the upper 4 cm of the sediment of Norsminde Fjord estuary, Denmark. A combination of C2H2 inhibition and 15N isotope techniques was used in intact sediment cores in short-term incubations (maximum, 4 h). The denitrification capacity exhibited two maxima, one in the spring and one in the fall, whereas the capacity for NO3− ammonification was maximal in the late summer, when sediments were progressively reduced. The denitrification capacity was always highest in the uppermost 1 cm of the sediment and declined with depth. The NO3− ammonification was usually higher with depth, but the maximum activity in late summer was observed within the upper 1 cm. The capacity for NO3− incorporation into organic material was investigated on two occasions in intact sediment cores and accounted for less than 5% of the total NO3− reduction. Denitrification accounted for between 13 and 51% of the total NO3− reduction, and NH4+ production accounted for between 4 and 21%, depending on initial rates during the time courses. Changes of the rates during the incubation were observed in the late summer, which reflected synthesis of denitrifying enzymes. This time lag was eliminated in experiments with mixed sediment because of preincubation with NO3− and alterations of the near-environmental conditions. The initial rates obtained in intact sediment cores therefore reflect the preexisting enzyme content of the sediment. 相似文献
7.
Correlation between Anammox Activity and Microscale Distribution of Nitrite in a Subtropical Mangrove Sediment 总被引:8,自引:2,他引:6 下载免费PDF全文
Rikke Louise Meyer Nils Risgaard-Petersen Diane Elizabeth Allen 《Applied microbiology》2005,71(10):6142-6149
The distribution of anaerobic ammonium oxidation (anammox) in nature has been addressed by only a few environmental studies, and our understanding of how anammox bacteria compete for substrates in natural environments is therefore limited. In this study, we measure the potential anammox rates in sediment from four locations in a subtropical tidal river system. Porewater profiles of NOx− (NO2− plus NO3−) and NO2− were measured with microscale biosensors, and the availability of NO2− was compared with the potential for anammox activity. The potential rate of anammox increased with increasing distance from the mouth of the river and correlated strongly with the production of nitrite in the sediment and with the average concentration or total pool of nitrite in the suboxic sediment layer. Nitrite accumulated both from nitrification and from NOx− reduction, though NOx− reduction was shown to have the greatest impact on the availability of nitrite in the suboxic sediment layer. This finding suggests that denitrification, though using NO2− as a substrate, also provides a substrate for the anammox process, which has been suggested in previous studies where microscale NO2− profiles were not measured. 相似文献
8.
M. Oshiki S. Ishii K. Yoshida N. Fujii M. Ishiguro H. Satoh S. Okabe 《Applied and environmental microbiology》2013,79(13):4087-4093
We examined nitrate-dependent Fe2+ oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of “Candidatus Brocadia sinica” anaerobically oxidized Fe2+ and reduced NO3− to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein−1 min−1, respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of “Ca. Brocadia sinica” (10 to 75 nmol NH4+ mg protein−1 min−1). A 15N tracer experiment demonstrated that coupling of nitrate-dependent Fe2+ oxidation and the anammox reaction was responsible for producing nitrogen gas from NO3− by “Ca. Brocadia sinica.” The activities of nitrate-dependent Fe2+ oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO3− ± SD of “Ca. Brocadia sinica” was determined to be 51 ± 21 μM. Nitrate-dependent Fe2+ oxidation was further demonstrated by another anammox bacterium, “Candidatus Scalindua sp.,” whose rates of Fe2+ oxidation and NO3− reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein−1 min−1, respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe2+ oxidation and the anammox reaction decreased the molar ratios of consumed NO2− to consumed NH4+ (ΔNO2−/ΔNH4+) and produced NO3− to consumed NH4+ (ΔNO3−/ΔNH4+). These reactions are preferable to the application of anammox processes for wastewater treatment. 相似文献
9.
Denitrification, Acetylene Reduction, and Methane Metabolism in Lake Sediment Exposed to Acetylene 总被引:8,自引:6,他引:2 下载免费PDF全文
Roger Knowles 《Applied microbiology》1979,38(3):486-493
Samples of sediment from Lake St. George, Ontario, Canada, were incubated in the laboratory under an initially aerobic gas phase and under anaerobic conditions. In the absence of added nitrate (NO3−) there was O2-dependent production of nitrous oxide (N2O), which was inhibited by acetylene (C2H2) and by nitrapyrin, suggesting that coupled nitrification-denitrification was responsible. Denitrification of added NO3− was almost as rapid under an aerobic gas phase as under anaerobic conditions. The N2O that accumulated persisted in the presence of 0.4 atm of C2H2, but was gradually reduced by some sediment samples at lower C2H2 concentrations. Low rates of C2H2 reduction were observed in the dark, were maximal at 0.2 atm of C2H2, and were decreased in the presence of O2, NO3−, or both. High rates of light-dependent C2H2 reduction occurred under anaerobic conditions. Predictably, methane (CH4) production, which occurred only under anaerobiosis, was delayed by added NO3− and inhibited by C2H2. Consumption of added CH4 occurred only under aerobic conditions and was inhibited by C2H2. 相似文献
10.
It has been hypothesized that under NO3− nutrition a high apoplastic pH in leaves depresses Fe3+ reductase activity and thus the subsequent Fe2+ transport across the plasmalemma, inducing Fe chlorosis. The apoplastic pH in young green leaves of sunflower (Helianthus annuus L.) was measured by fluorescence ratio after xylem sap infiltration. It was shown that NO3− nutrition significantly increased apoplastic pH at distinct interveinal sites (pH ≥ 6.3) and was confined to about 10% of the whole interveinal leaf apoplast. These apoplastic pH increases presumably derive from NO3−/proton cotransport and are supposed to be related to growing cells of a young leaf; they were not found in the case of sole NH4+ or NH4NO3 nutrition. Complementary to pH measurements, the formation of Fe2+-ferrozine from Fe3+-citrate was monitored in the xylem apoplast of intact leaves in the presence of buffers at different xylem apoplastic pH by means of image analysis. This analysis revealed that Fe3+ reduction increased with decreasing apoplastic pH, with the highest rates at around pH 5.0. In analogy to the monitoring of Fe3+ reduction in the leaf xylem, we suggest that under alkaline nutritional conditions at interveinal microsites of increased apoplastic pH, Fe3+ reduction is depressed, inducing leaf chlorosis. The apoplastic pH in the xylem vessels remained low in the still-green veins of leaves with intercostal chlorosis. 相似文献
11.
Microbial Iron Reduction by Enrichment Cultures Isolated from Estuarine Sediments 总被引:7,自引:6,他引:1 下载免费PDF全文
Microbial Fe reduction in acetate- and succinate-containing enrichment cultures initiated with an estuarine sediment inoculum was studied. Fe reduction was unaffected when SO42− reduction was inhibited by MoO42−, indicating that both processes could occur independently. Bacterially produced sulfide precipitated as FeS but was not completely responsible for Fe reduction. The separation of oxidized Fe particles from bacteria by dialysis tubing demonstrated that direct bacterial contact was necessary for Fe reduction. Fe reduction in cultures amended with NO3− was delayed until NO3− and NO2− were removed. However, bacterial attachment to oxidized Fe particles in NO3−-amended cultures occurred early during growth in a manner similar to NO3−-free cultures. During late stages of growth, bacteria not attached to Fe particles became pale and swollen, while attached cells remained bright blue when examined by 4′,6-diamidine-2-phenylindole epifluo-rescence microscopy. The presence of added oxidized Mn had no effect on Fe reduction. The results suggested that enzymatic Fe reduction was responsible for reducing Fe in these cultures even in the presence of sulfide and that cells incapable of Fe reduction became unhealthy when Fe(III) was the only available electron acceptor. 相似文献
12.
Bacterial sulfate reduction in the surface sediment and the water column of Lake Mendota, Madison, Wis., was studied by using radioactive sulfate (35SO42−). High rates of sulfate reduction were observed at the sediment surface, where the sulfate pool (0.2 mM SO42−) had a turnover time of 10 to 24 h. Daily sulfate reduction rates in Lake Mendota sediment varied from 50 to 600 nmol of SO42− cm−3, depending on temperature and sampling date. Rates of sulfate reduction in the water column were 103 times lower than that for the surface sediment and, on an areal basis, accounted for less than 18% of the total sulfate reduction in the hypolimnion during summer stratification. Rates of bacterial sulfate reduction in the sediment were not sulfate limited at sulfate concentrations greater than 0.1 mM in short-term experiments. Although sulfate reduction seemed to be sulfate limited below 0.1 mM, Michaelis-Menten kinetics were not observed. The optimum temperature (36 to 37°C) for sulfate reduction in the sediment was considerably higher than in situ temperatures (1 to 13°C). The response of sulfate reduction to the addition of various electron donors metabolized by sulfate-reducing bacteria in pure culture was investigated. The degree of stimulation was in this order: H2 > n-butanol > n-propanol > ethanol > glucose. Acetate and lactate caused no stimulation. 相似文献
13.
M. Scott Smith 《Applied microbiology》1982,43(4):854-860
Dissimilatory reduction of NO2− to N2O and NH4+ by a soil Citrobacter sp. was studied in an attempt to elucidate the physiological and ecological significance of N2O production by this mechanism. In batch cultures with defined media, NO2− reduction to NH4+ was favored by high glucose and low NO3− concentrations. Nitrous oxide production was greatest at high glucose and intermediate NO3− concentrations. With succinate as the energy source, little or no NO2− was reduced to NH4+ but N2O was produced. Resting cell suspensions reduced NO2− simultaneously to N2O and free extracellular NH4+. Chloramphenicol prevented the induction of N2O-producing activity. The Km for NO2− reduction to N2O was estimated to be 0.9 mM NO2−, yet the apparent Km for overall NO2− reduction was considerably lower, no greater than 0.04 mM NO2−. Activities for N2O and NH4+ production increased markedly after depletion of NO3− from the media. Amendment with NO3− inhibited N2O and NH4+ production by molybdate-grown cells but not by tungstate-grown cells. Sulfite inhibited production of NH4+ but not of N2O. In a related experiment, three Escherichia coli mutants lacking NADH-dependent nitrite reductase produced N2O at rates equal to the wild type. These observations suggest that N2O is produced enzymatically but not by the same enzyme system responsible for dissimilatory reduction of NO2− to NH4+. 相似文献
14.
Chemical and Biological Interactions during Nitrate and Goethite Reduction by Shewanella putrefaciens 200 下载免费PDF全文
D. Craig Cooper Flynn W. Picardal Arndt Schimmelmann Aaron J. Coby 《Applied microbiology》2003,69(6):3517-3525
Although previous research has demonstrated that NO3− inhibits microbial Fe(III) reduction in laboratory cultures and natural sediments, the mechanisms of this inhibition have not been fully studied in an environmentally relevant medium that utilizes solid-phase, iron oxide minerals as a Fe(III) source. To study the dynamics of Fe and NO3− biogeochemistry when ferric (hydr)oxides are used as the Fe(III) source, Shewanella putrefaciens 200 was incubated under anoxic conditions in a low-ionic-strength, artificial groundwater medium with various amounts of NO3− and synthetic, high-surface-area goethite. Results showed that the presence of NO3− inhibited microbial goethite reduction more severely than it inhibited microbial reduction of the aqueous or microcrystalline sources of Fe(III) used in other studies. More interestingly, the presence of goethite also resulted in a twofold decrease in the rate of NO3− reduction, a 10-fold decrease in the rate of NO2− reduction, and a 20-fold increase in the amounts of N2O produced. Nitrogen stable isotope experiments that utilized δ15N values of N2O to distinguish between chemical and biological reduction of NO2− revealed that the N2O produced during NO2− or NO3− reduction in the presence of goethite was primarily of abiotic origin. These results indicate that concomitant microbial Fe(III) and NO3− reduction produces NO2− and Fe(II), which then abiotically react to reduce NO2− to N2O with the subsequent oxidation of Fe(II) to Fe(III). 相似文献
15.
Selenate Reduction to Elemental Selenium by Anaerobic Bacteria in Sediments and Culture: Biogeochemical Significance of a Novel, Sulfate-Independent Respiration 总被引:19,自引:12,他引:7 下载免费PDF全文
Ronald S. Oremland James T. Hollibaugh Ann S. Maest Theresa S. Presser Laurence G. Miller Charles W. Culbertson 《Applied microbiology》1989,55(9):2333-2343
Interstitial water profiles of SeO42−, SeO32−, SO42−, 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 SeO42− occurred under anaerobic conditions, was more rapid with H2 or acetate, and was inhibited by O2, NO3−, MnO2, or autoclaving but not by SO42− 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 MnO2. 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
16.
Seigo Amachi Nahito Kawaguchi Yasuyuki Muramatsu Satoshi Tsuchiya Yuko Watanabe Hirofumi Shinoyama Takaaki Fujii 《Applied microbiology》2007,73(18):5725-5730
Bacterial iodate (IO3−) reduction is poorly understood largely due to the limited number of available isolates as well as the paucity of information about key enzymes involved in the reaction. In this study, an iodate-reducing bacterium, designated strain SCT, was newly isolated from marine sediment slurry. SCT is phylogenetically closely related to the denitrifying bacterium Pseudomonas stutzeri and reduced 200 μM iodate to iodide (I−) within 12 h in an anaerobic culture containing 10 mM nitrate. The strain did not reduce iodate under the aerobic conditions. An anaerobic washed cell suspension of SCT reduced iodate when the cells were pregrown anaerobically with 10 mM nitrate and 200 μM iodate. However, cells pregrown without iodate did not reduce it. The cells in the former category showed methyl viologen-dependent iodate reductase activity (0.31 U mg−1), which was located predominantly in the periplasmic space. Furthermore, SCT was capable of anaerobic growth with 3 mM iodate as the sole electron acceptor, and the cells showed enhanced activity with respect to iodate reductase (2.46 U mg−1). These results suggest that SCT is a dissimilatory iodate-reducing bacterium and that its iodate reductase is induced by iodate under anaerobic growth conditions. 相似文献
17.
Role of Sulfate Reduction Versus Methanogenesis in Terminal Carbon Flow in Polluted Intertidal Sediment of Waimea Inlet, Nelson, New Zealand 总被引:9,自引:9,他引:0 下载免费PDF全文
An investigation of the terminal anaerobic processes occurring in polluted intertidal sediments indicated that terminal carbon flow was mainly mediated by sulfate-reducing organisms in sediments with high sulfate concentrations (>10 mM in the interstitial water) exposed to low loadings of nutrient (equivalent to <102 kg of N · day−1) and biochemical oxygen demand (<0.7 × 103 kg · day−1) in effluents from different pollution sources. However, in sediments exposed to high loadings of nutrient (>102 kg of N · day−1) and biochemical oxygen demand (>0.7 × 103 kg · day−1), methanogenesis was the major process in the mediation of terminal carbon flow, and sulfate concentrations were low (≤2 mM). The respiratory index [14CO2/(14CO2 + 14CH4)] for [2-14C]acetate catabolism, a measure of terminal carbon flow, was ≥0.96 for sediment with high sulfate, but in sediments with sulfate as little as 10 μM in the interstitial water, respiratory index values of ≤0.22 were obtained. In the latter sediment, methane production rates as high as 3 μmol · g−1 (dry weight) · h−1 were obtained, and there was a potential for active sulfate reduction. 相似文献
18.
Dissimilatory Selenate Reduction Potentials in a Diversity of Sediment Types 总被引:8,自引:6,他引:2 下载免费PDF全文
We measured potential rates of bacterial dissimilatory reduction of 75SeO42− to 75Se0 in a diversity of sediment types, with salinities ranging from freshwater (salinity = 1 g/liter) to hypersaline (salinity = 320 g/liter and with pH values ranging from 7.1 to 9.8. Significant biological selenate reduction occurred in all samples with salinities from 1 to 250 g/liter but not in samples with a salinity of 320 g/liter. Potential selenate reduction rates (25 nmol of SeO42− per ml of sediment added with isotope) ranged from 0.07 to 22 μmol of SeO42− reduced liter−1 h−1. Activity followed Michaelis-Menten kinetics in relation to SeO42− concentration (Km of selenate = 7.9 to 720 μM). There was no linear correlation between potential rates of SeO42− reduction and salinity, pH, concentrations of total Se, porosity, or organic carbon in the sediments. However, potential selenate reduction was correlated with apparent Km for selenate and with potential rates of denitrification (r = 0.92 and 0.81, respectively). NO3−, NO2−, MoO42−, and WO42− inhibited selenate reduction activity to different extents in sediments from both Hunter Drain and Massie Slough, Nev. Sulfate partially inhibited activity in sediment from freshwater (salinity = 1 g/liter) Massie Slough samples but not from the saline (salinity = 60 g/liter) Hunter Drain samples. We conclude that dissimilatory selenate reduction in sediments is widespread in nature. In addition, in situ selenate reduction is a first-order reaction, because the ambient concentrations of selenium oxyanions in the sediments were orders of magnitude less than their Kms. 相似文献
19.
Nitrate Reduction in a Groundwater Microcosm Determined by 15N Gas Chromatography-Mass Spectrometry 总被引:1,自引:0,他引:1 下载免费PDF全文
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 NO3−-N liter−1. Traces of 15NO3− 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 15N2, 15N2O, 15NH4+, and 15N-labeled protein amino acids by capillary gas chromatography-mass spectrometry. N2 and N2O were separated on a megabore fused-silica column and quantified by electron impact-selected ion monitoring. NO3− and NH4+ 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 N2, whereas only 35% was denitrified in the anaerobic microcosm, where more than 50% of NO3− was reduced to NH4+. 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
20.
Nitrate Reduction in Roots as Affected by the Presence of Potassium and by Flux of Nitrate through the Roots 总被引:9,自引:5,他引:4 下载免费PDF全文
Dark-grown, detopped corn seedlings (cv. Pioneer 3369A) were exposed to treatment solutions containing Ca(NO3)2, NaNO3, or KNO3; KNO3 plus 50 or 100 millimolar sorbitol; and KNO3 at root temperatures of 30, 22, or 16 C. In all experiments, the accelerated phase of NO3− transport had previously been induced by prior exposure to NO3− for 10 hours. The experimental system allowed direct measurements of net NO3− uptake and translocation, and calculation of NO3− reduction in the root. The presence of K+ resulted in small increases in NO3− uptake, but appreciably stimulated NO3− translocation out of the root. Enhanced translocation was associated with a marked decrease in the proportion of absorbed NO3− that was reduced in the root. When translocation was slowed by osmoticum or by low root temperatures, a greater proportion of absorbed NO3− was reduced in the presence of K+. Results support the proposition that NO3− reduction in the root is reciprocally related to the rate of NO3− transport through the root symplasm. 相似文献