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1.
A microscale biosensor for acetate, propionate, isobutyrate, and lactate is described. The sensor is based on the bacterial respiration of low-molecular-weight, negatively charged species with a concomitant reduction of NO 3− to N 2O. A culture of denitrifying bacteria deficient in N 2O reductase was immobilized in front of the tip of an electrochemical N 2O microsensor. The bacteria were separated from the outside environment by an ion-permeable membrane and supplied with nutrients (except for electron donors) from a medium reservoir behind the N 2O sensor. The signal of the sensor, which corresponded to the rate of N 2O production, was proportional to the supply of the electron donor to the bacterial mass. The selectivity for volatile fatty acids compared to other organic compounds was increased by selectively enhancing the transport of negatively charged compounds into the sensor by electrophoretic migration (electrophoretic sensitivity control). The sensor was susceptible to interference from O 2, N 2O, NO 2−, H 2S, and NO 3−. Interference from NO 3− was low and could be quantified and accounted for. The detection limit was equivalent to about 1 μM acetate, and the 90% response time was 30 to 90 s. The response of the sensor was not affected by changes in pH between 5.5 and 9 and was also unaffected by changes in salinity in the range of 2 to 32‰. The functioning of the sensor over a temperature span of 7 to 30°C was investigated. The concentration range for a linear response was increased five times by increasing the temperature from 7 to 19.5°C. The life span of the biosensor varied between 1 and 3 weeks after manufacturing. 相似文献
2.
Dissimilatory reduction of NO 2− to N 2O and NH 4+ by a soil Citrobacter sp. was studied in an attempt to elucidate the physiological and ecological significance of N 2O production by this mechanism. In batch cultures with defined media, NO 2− reduction to NH 4+ was favored by high glucose and low NO 3− concentrations. Nitrous oxide production was greatest at high glucose and intermediate NO 3− concentrations. With succinate as the energy source, little or no NO 2− was reduced to NH 4+ but N 2O was produced. Resting cell suspensions reduced NO 2− simultaneously to N 2O and free extracellular NH 4+. Chloramphenicol prevented the induction of N 2O-producing activity. The Km for NO 2− reduction to N 2O was estimated to be 0.9 mM NO 2−, yet the apparent Km for overall NO 2− reduction was considerably lower, no greater than 0.04 mM NO 2−. Activities for N 2O and NH 4+ production increased markedly after depletion of NO 3− from the media. Amendment with NO 3− inhibited N 2O and NH 4+ production by molybdate-grown cells but not by tungstate-grown cells. Sulfite inhibited production of NH 4+ but not of N 2O. In a related experiment, three Escherichia coli mutants lacking NADH-dependent nitrite reductase produced N 2O at rates equal to the wild type. These observations suggest that N 2O is produced enzymatically but not by the same enzyme system responsible for dissimilatory reduction of NO 2− to NH 4+. 相似文献
3.
Most studies of bacterial denitrification have used nitrate (NO 3−) as the first electron acceptor, whereas relatively less is understood about nitrite (NO 2−) denitrification. We isolated novel bacteria that proliferated in the presence of high levels of NO 2− (72 mM). Strain YD50.2, among several isolates, was taxonomically positioned within the α subclass of Proteobacteria and identified as Ochrobactrum anthropi YD50.2. This strain denitrified NO 2−, as well as NO 3−. The gene clusters for denitrification ( nar, nir, nor, and nos) were cloned from O. anthropi YD50.2, in which the nir and nor operons were linked. We confirmed that nirK in the nir- nor operon produced a functional NO 2− reductase containing copper that was involved in bacterial NO 2− reduction. The strain denitrified up to 40 mM NO 2− to dinitrogen under anaerobic conditions in which other denitrifiers or NO 3− reducers such as Pseudomonas aeruginosa and Ralstonia eutropha and nitrate-respiring Escherichia coli neither proliferated nor reduced NO 2−. Under nondenitrifying aerobic conditions, O. anthropi YD50.2 and its type strain ATCC 49188 T proliferated even in the presence of higher levels of NO 2− (100 mM), and both were considerably more resistant to acidic NO 2− than were the other strains noted above. These results indicated that O. anthropi YD50.2 is a novel denitrifier that has evolved reactive nitrogen oxide tolerance mechanisms.Environmental bacteria maintain the global nitrogen cycle by metabolizing organic and inorganic nitrogen compounds. Denitrification is critical for maintenance of the global nitrogen cycle, through which nitrate (NO 3−) or nitrite (NO 2−) is reduced to gaseous nitrogen forms such as N 2 and nitrous oxide (N 2O) ( 19, 47). Decades of investigations into denitrifying bacteria have revealed their ecological impact ( 9), their molecular mechanisms of denitrification ( 13, 25, 47), and the industrial importance of removing nitrogenous contaminants from wastewater ( 31, 36). Bacterial denitrification is considered to comprise four successive reduction steps, each of which is catalyzed by NO 3− reductase (Nar), NO 2− reductase (Nir), nitric oxide (NO) reductase (Nor), and N 2O reductase (Nos). The reaction of each enzyme is linked to the electron transport chain on the cellular membrane and accompanies oxidative phosphorylation, implying that bacterial denitrification is of as much physiological significance as anaerobic respiration ( 25, 47). Most denitrifying bacteria are facultative anaerobes and respire with oxygen under aerobic conditions. Because denitrification is induced in the absence of oxygen, it is considered an alternative mechanism of energy conservation that has evolved as an adaptation to anaerobic circumstances ( 13, 47).Nitrite and NO are hazardous to bacteria, since they generate highly reactive nitrogen species (RNS) under physiological conditions and damage cellular DNA, lipid, and proteins ( 28, 37). Denitrifying bacteria are thought to be threatened by RNS since they reduce NO 3− to generate NO 2− and NO as denitrifying intermediates. Furthermore, denitrifying bacteria often inhabit environments where they are exposed to NO 2− and NO and hence high levels of RNS. Recent reports suggest that pathogenic bacteria invading animal tissues are attacked by NO generated by macrophages ( 12). Such bacteria involve denitrifiers, and some of them, for example, Neisseria meningitidis ( 1) and Pseudomonas aeruginosa, acquire resistance to NO by producing Nor ( 44). The utilization (reduction) of NO by Brucella increases the survival of infected mice ( 2). These examples suggest that production of a denitrifying mechanism affects bacterial survival of threats from both endogenous and extracellular RNS. However, the mechanism of RNS tolerance induced by denitrifying bacteria is not fully understood.Ubiquitous gram-negative Ochrobactrum strains are widely distributed in soils and aqueous environments, where they biodegrade aromatic compounds ( 11), organophosphorus pesticides ( 45), and other hydrocarbons ( 38) and remove heavy metal ions such as chromium and cadmium ( 24). Having been isolated from clinical specimens, Ochrobactrum anthropi is currently recognized as an emerging opportunistic pathogen, although relatively little is known about its pathogenesis and factors contributing to its virulence ( 7, 30). Manipulation systems have been developed to investigate these issues at the molecular genetic level ( 33). Some O. anthropi strains have been identified as denitrifiers ( 21), although the denitrifying properties of these strains have not been investigated in detail. This study was undertaken to examine the denitrifying properties of O. anthropi in more detail. O. anthropi YD50.2 was selected for this study and was isolated herein. The strain denitrified high levels of NO 2− (up to 40 mM) to dinitrogen under anaerobic conditions. The strain was highly resistant to acidified NO 2− under nondenitrifying aerobic conditions. These results indicate that O. anthropi YD50.2 has mechanisms that produce tolerance to RNS. 相似文献
4.
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 NO 3− + NO 2− concentrations (≤26 μM) were below the apparent Km (50 μM) for nitrate. During the rainy season, when ambient NO 3− + NO 2− 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 N 2O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N 2O in the presence of C 2H 2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N 2O loss was caused by incomplete blockage of N 2O reductase by C 2H 2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N 2 m −2 h −1 (for undisturbed sediments) to 17 to 280 μmol of N 2 m −2 h −1 (for shaken sediment slurries). 相似文献
5.
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
6.
Although denitrification or nitrate respiration has been found among a few eukaryotes, its phylogenetic relationship with the bacterial system remains unclear because orthologous genes involved in the bacterial denitrification system were not identified in these eukaryotes. In this study, we isolated a gene from the denitrifying fungus Fusarium oxysporum that is homologous to the bacterial nirK gene responsible for encoding copper-containing nitrite reductase (NirK). Characterization of the gene and its recombinant protein showed that the fungal nirK gene is the first eukaryotic ortholog of the bacterial counterpart involved in denitrification. Additionally, recent genome analyses have revealed the occurrence of nirK homologs in many fungi and protozoa, although the denitrifying activity of these eukaryotes has never been examined. These eukaryotic homolog genes, together with the fungal nirK gene of F. oxysporum, are grouped in the same branch of the phylogenetic tree as the nirK genes of bacteria, archaea, and eukaryotes, implying that eukaryotic nirK and its homologs evolved from a single ancestor (possibly the protomitochondrion). These results show that the fungal denitrifying system has the same origin as its bacterial counterpart.Denitrification plays an important role in the global nitrogen cycle and reduces nitrate (NO 3−) and/or nitrite (NO 2−) to a gaseous form of nitrogen, generally to dinitrogen (N 2) or nitrous oxide (N 2O) ( 27). It typically follows four reduction stages, NO 3− → NO 2− → NO → N 2O → N 2, each of which is catalyzed by a specific reductase: dissimilatory NO 3− reductase (dNaR), dissimilatory NO 2− reductase (dNiR), nitric oxide (NO) reductase (NoR), and N 2O reductase, respectively. These enzymes receive electrons from a respiratory chain functioning as a “terminal reductase.” Thus, denitrification exhibits a physiological significance in its ability to anaerobically respire through the processes of nitrate respiration, nitrite respiration, and so forth. Denitrification was previously thought to be a characteristic of bacteria; however, similar reactions have been found to occur in a few eukaryotes and archaea ( 6, 27). Eukaryotic nitrate respiration was first found in protozoa that reside in an anaerobic freshwater habitat ( 8). The organism particularly reduces NO 3− to NO 2− in a single step, a process which recovers dNaR activity in the mitochondrial fraction but does not result in denitrification. Eukaryotic denitrification was first found to occur among fungi ( 19, 20), which generally form N 2O from NO 3− or NO 2−. Recently, eukaryotic denitrification was also found in a benthic foraminifer that forms N 2 from NO 3− ( 18). The fungal denitrification system localizes in the mitochondria and couples to the mitochondrial electron transport chain to produce ATP ( 12, 21), thus exhibiting properties similar to those of the bacterial systems in its ability to respire anaerobically. Moreover, the mechanism of anaerobic respiration in the “aerobic” organelle of eukaryotes (mitochondrion) evokes interest regarding the origin and evolution of the mitochondrion.The main components of the fungal denitrifying system, the dNaR, dNiR, and NoR proteins, were either completely or partially purified from Fusarium oxysporum. Fungal NoR of the cytochrome P450 (P450) type, referred to as P450nor (CYP55) ( 11, 16), is a distinct species of bacterial cytochrome cb-type NoR. By contrast, the previously isolated fungal dNiR protein is a copper-containing type (NirK) that closely resembles its bacterial counterpart ( 13). Furthermore, dNaR activity partially purified from the mitochondrial membrane fraction showed that fungal dNaR possibly resembles its bacterial counterpart, NarGHI ( 12, 23). Therefore, while a portion of the fungal system appears to resemble its bacterial counterpart, the phylogenetic relationship between the fungal and bacterial denitrification systems remained unclear because the genes of the fungal components (dNaR and dNiR) have not been sequenced.Recent genome analyses have revealed the presence of nirK homolog genes in many eukaryotes (fungi and protozoa), a finding consistent with our previous findings on the isolation of the fungal NirK protein ( 13). Therefore, whether these eukaryotes containing the nirK homolog gene exhibit denitrification activity and whether the denitrifying fungus F. oxysporum really contains a nirK gene deserve a great deal of attention. To address this issue, we used the suppression subtractive hybridization (SSH) technique ( 7) and succeeded in isolating the nirK gene from the denitrifying fungus F. oxysporum. 相似文献
7.
We screened soybean rhizobia originating from three germplasm collections for the ability to grow anaerobically in the presence of NO 3− and for differences in final product formation from anaerobic NO 3− metabolism. Denitrification abilities of selected strains as free-living bacteria and as bacteroids were compared. Anaerobic growth in the presence of NO 3− was observed in 270 of 321 strains of soybean rhizobia. All strains belonging to the 135 serogroup did not grow anaerobically in the presence of NO 3−. An investigation with several strains indicated that bacteria not growing anaerobically in the presence of NO 3− also did not utilize NO 3− as the sole N source aerobically. An exception was strain USDA 33, which grew on NO 3− but failed to denitrify. Dissimilation of NO 3− by the free-living cultures proceeded without the significant release of intermediate products. Nitrous oxide reductase was inhibited by C 2H 2, but preceding steps of denitrification were not affected. Final products of denitrification were NO 2−, N 2O, or N 2; serogroups 31, 46, 76, and 94 predominantly liberated NO 2−, whereas evolution of N 2 was prevalent in serogroups 110 and 122, and all three were formed as final products by strains belonging to serogroups 6 and 123. Anaerobic metabolism of NO 3− by bacteroid preparations of Bradyrhizobium japonicum proceeded without delay and was evident by NO 2− accumulation irrespective of which final product was formed by the strain as free-living bacteria. Anaerobic C 2H 2 reduction in the presence of NO 3− was observed in bacteroid preparations capable of NO 3− respiration but was absent in bacteria that were determined to be deficient in dissimilatory nitrate reductase. 相似文献
8.
Using a combination of process rate determination, microsensor profiling and molecular techniques, we demonstrated that denitrification, and not anaerobic ammonium oxidation (anammox), is the major nitrogen loss process in biological soil crusts from Oman. Potential denitrification rates were 584±101 and 58±20 μmol N m −2 h −1 for cyanobacterial and lichen crust, respectively. Complete denitrification to N 2 was further confirmed by an 15NO 3− tracer experiment with intact crust pieces that proceeded at rates of 103±19 and 27±8 μmol N m −2 h −1 for cyanobacterial and lichen crust, respectively. Strikingly, N 2O gas was emitted at very high potential rates of 387±143 and 31±6 μmol N m −2 h −1 from the cyanobacterial and lichen crust, respectively, with N 2O accounting for 53–66% of the total emission of nitrogenous gases. Microsensor measurements revealed that N 2O was produced in the anoxic layer and thus apparently originated from incomplete denitrification. Using quantitative PCR, denitrification genes were detected in both the crusts and were expressed either in comparable ( nirS) or slightly higher ( narG) numbers in the cyanobacterial crusts. Although 99% of the nirS sequences in the cyanobacterial crust were affiliated to an uncultured denitrifying bacterium, 94% of these sequences were most closely affiliated to Paracoccus denitrificans in the lichen crust. Sequences of nosZ gene formed a distinct cluster that did not branch with known denitrifying bacteria. Our results demonstrate that nitrogen loss via denitrification is a dominant process in crusts from Oman, which leads to N 2O gas emission and potentially reduces desert soil fertility. 相似文献
9.
Two fast-growing strains of cowpea rhizobia (A26 and A28) were found to grow anaerobically at the expense of NO 3−, NO 2−, and N 2O as terminal electron acceptors. The two major differences between aerobic and denitrifying growth were lower yield coefficients ( Y) and higher saturation constants ( Ks) with nitrogenous oxides as electron acceptors. When grown aerobically, A26 and A28 adhered to Monod kinetics, respectively, as follows: Ks, 3.4 and 3.8 μM; Y, 16.0 and 14.0 g · cells eq −1; μ max, 0.41 and 0.33 h −1. Yield coefficients for denitrifying growth ranged from 40 to 70% of those for aerobic growth. Only A26 adhered to Monod kinetics with respect to growth on all three nitrogenous oxides. The apparent Ks values were 41, 270, and 460 μM for nitrous oxide, nitrate, and nitrite, respectively; the Ks for A28 grown on nitrate was 250 μM. The results are kinetically and thermodynamically consistent in explaining why O 2 is the preferred electron acceptor. Although no definitive conclusions could be drawn regarding preferential utilization of nitrogenous oxides, nitrite was inhibitory to both strains and effected slower growth. However, growth rates were identical (μ max, 0.41 h −1) when A26 was grown with either O 2 or NO 3− as an electron acceptor and were only slightly reduced when A28 was grown with NO 3− (0.25 h −1) as opposed to O 2 (0.33 h −1). 相似文献
10.
A more sensitive analytical method for NO 3− was developed based on the conversion of NO 3− to N 2O by a denitrifier that could not reduce N 2O further. The improved detectability resulted from the high sensitivity of the 63Ni electron capture gas chromatographic detector for N 2O and the purification of the nitrogen afforded by the transformation of the N to a gaseous product with a low atmospheric background. The selected denitrifier quantitatively converted NO 3− to N 2O within 10 min. The optimum measurement range was from 0.5 to 50 ppb (50 μg/liter) of NO 3− N, and the detection limit was 0.2 ppb of N. The values measured by the denitrifier method compared well with those measured by the high-pressure liquid chromatographic UV method above 2 ppb of N, which is the detection limit of the latter method. It should be possible to analyze all types of samples for nitrate, except those with inhibiting substances, by this method. To illustrate the use of the denitrifier method, NO 3− concentrations of <2 ppb of NO 3− N were measured in distilled and deionized purified water samples and in anaerobic lake water samples, but were not detected at the surface of the sediment. The denitrifier method was also used to measure the atom% of 15N in NO 3−. This method avoids the incomplete reduction and contamination of the NO 3− -N by the NH 4+ and N 2 pools which can occur by the conventional method of 15NO 3− analysis. N 2O-producing denitrifier strains were also used to measure the apparent Km values for NO 3− use by these organisms. Analysis of N 2O production by use of a progress curve yielded Km values of 1.7 and 1.8 μM NO 3− for the two denitrifier strains studied. 相似文献
11.
Soil emissions are largely responsible for the increase of the potent greenhouse gas nitrous oxide (N 2O) in the atmosphere and are generally attributed to the activity of nitrifying and denitrifying bacteria. However, the contribution of the recently discovered ammonia-oxidizing archaea (AOA) to N 2O production from soil is unclear as is the mechanism by which they produce it. Here we investigate the potential of Nitrososphaera viennensis, the first pure culture of AOA from soil, to produce N 2O and compare its activity with that of a marine AOA and an ammonia-oxidizing bacterium (AOB) from soil . N. viennensis produced N 2O at a maximum yield of 0.09% N 2O per molecule of nitrite under oxic growth conditions. N 2O production rates of 4.6±0.6 amol N 2O cell −1 h −1 and nitrification rates of 2.6±0.5 fmol NO 2− cell −1 h −1 were in the same range as those of the AOB Nitrosospira multiformis and the marine AOA Nitrosopumilus maritimus grown under comparable conditions. In contrast to AOB, however, N 2O production of the two archaeal strains did not increase when the oxygen concentration was reduced, suggesting that they are not capable of denitrification. In 15N-labeling experiments we provide evidence that both ammonium and nitrite contribute equally via hybrid N 2O formation to the N 2O produced by N. viennensis under all conditions tested. Our results suggest that archaea may contribute to N 2O production in terrestrial ecosystems, however, they are not capable of nitrifier-denitrification and thus do not produce increasing amounts of the greenhouse gas when oxygen becomes limiting. 相似文献
12.
Aquaspirillum magnetotacticum MS-1 grew microaerobically but not anaerobically with NO 3− or NH 4+ as the sole nitrogen source. Nevertheless, cell yields varied directly with NO 3− concentration under microaerobic conditions. Products of NO 3− reduction included NH 4+, N 2O, NO, and N 2. NO 2− and NH 2OH, each toxic to cells at 0.2 mM, were not detected as products of cells growing on NO 3−. NO 3− reduction to NH 4+ was completely repressed by the addition of 2 mM NH 4+ to the growth medium, whereas NO 3− reduction to N 2O or to N 2 was not. C 2H 2 completely inhibited N 2O reduction to N 2 by growing cells. These results indicate that A. magnetotacticum is a microaerophilic denitrifier that is versatile in its nitrogen metabolism, concomitantly reducing NO 3− by assimilatory and dissimilatory means. This bacterium appears to be the first described denitrifier with an absolute requirement for O 2. The process of NO 3− reduction appears well adapted for avoiding accumulation of several nitrogenous intermediates that are toxic to cells. 相似文献
13.
Microsensors, including a recently developed NO 3− biosensor, were applied to measure O 2 and NO 3− profiles in marine sediments from the upwelling area off central Chile and to investigate the influence of Thioploca spp. on the sedimentary nitrogen metabolism. The studies were performed in undisturbed sediment cores incubated in a small laboratory flume to simulate the environmental conditions of low O 2, high NO 3−, and bottom water current. On addition of NO 3− and NO 2−, Thioploca spp. exhibited positive chemotaxis and stretched out of the sediment into the flume water. In a core densely populated with Thioploca, the penetration depth of NO 3− was only 0.5 mm and a sharp maximum of NO 3− uptake was observed 0.5 mm above the sediment surface. In sediments with only few Thioploca spp., NO 3− was detectable down to a depth of 2 mm and the maximum consumption rates were observed within the sediment. No chemotaxis toward nitrous oxide (N 2O) was observed, which is consistent with the observation that Thioploca does not denitrify but reduces intracellular NO 3− to NH 4+. Measurements of the intracellular NO 3− and S 0 pools in Thioploca filaments from various depths in the sediment gave insights into possible differences in the migration behavior between the different species. Living filaments containing significant amounts of intracellular NO 3− were found to a depth of at least 13 cm, providing final proof for the vertical shuttling of Thioploca spp. and nitrate transport into the sediment. 相似文献
14.
One host ( Rana catesbiana)-associated and two free-living mesophilic strains of bacteria with violet pigmentation and biochemical characteristics of Chromobacterium violaceum were isolated from freshwater habitats. Cells of each freshly isolated strain and of strain ATCC 12472 (the neotype strain) grew anaerobically with glucose as the sole carbon and energy source. The major fermentation products of cells grown in Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) supplemented with glucose included acetate, small amounts of propionate, lactate, and pyruvate. The final cell yield and culture growth rate of each strain cultured anaerobically in this medium increased approximately twofold with the addition of 2 mM NaNO 3. Final growth yields increased in direct proportion to the quantity of added NaNO 3 over the range of 0.5 to 5 mM. Each strain reduced NO 3−, producing NO 2−, NO, and N 2O. NO 2− accumulated transiently. With 2 mM NaNO 3 in the medium, N 2O made up 85 to 98% of the N product recovered with each strain. N-oxides were recovered in the same quantity and distribution whether 0.01 atm (ca. 1 kPa) of C 2H 2 (added to block N 2O reduction) was present or not. Neither N 2 production nor gas accumulation was detected during NO 3− reduction by growing cells. Cell growth in media containing 0.5 to 5 mM NaNO 2 in lieu of NaNO 3 was delayed, and although N 2O was produced by the end of growth, NO 2− -containing media did not support growth to an extent greater than did medium lacking NO 3− or NO 2−. The data indicate that C. violaceum cells ferment glucose or denitrify, terminating denitrification with the production of N 2O, and that NO 2− reduction to N 2O is not coupled to growth but may serve as a detoxification mechanism. No strain detectably fixed N 2 (reduced C 2H 2). 相似文献
15.
Natural denitrification rates and activities of denitrifying enzymes were measured in an agricultural soil which had a 20-year past history of low pH (pH ca. 4) due to fertilization with acid-generating ammonium salts. The soil adjacent to this site had been limed and had a pH of ca. 6.0. Natural denitrification rates of these areas were of similar magnitude: 158 ng of N g −1 of soil day −1 for the acid soil and 390 ng of N g −1 of soil day −1 at the neutral site. Estimates of in situ denitrifying enzyme activity were higher in the neutral soil, but substantial enzyme activity was also detected in the acid soil. Rates of nitrous oxide reduction were very low, even when NO 3− and NO 2− were undetectable, and were ca. 400 times lower than the rates of N 2O production from NO 3−. Denitrification rates measured in slurries of the acid and neutral soil showed distinctly different pH optima (pH 3.9 and pH 6.3) which were near the pH values of the two soils. This suggests that an acid-tolerant denitrifying population had been selected during the 20-year period of low pH. 相似文献
17.
Pure cultures of the marine ammonium-oxidizing bacterium Nitrosomonas sp. were grown in the laboratory at oxygen partial pressures between 0.005 and 0.2 atm (0.18 to 7 mg/liter). Low oxygen conditions induced a marked decrease in the rate for production of NO 2-, from 3.6 × 10 −10 to 0.5 × 10 −10 mmol of NO 2- per cell per day. In contrast, evolution of N 2O increased from 1 × 10 −12 to 4.3 × 10 −12 mmol of N per cell per day. The yield of N 2O relative to NO 2- increased from 0.3% to nearly 10% (moles of N in N 2O per mole of NO 2-) as the oxygen level was reduced, although bacterial growth rates changed by less than 30%. Nitrifying bacteria from the genera Nitrosomonas, Nitrosolobus, Nitrosospira, and Nitrosococcus exhibited similar yields of N 2O at atmospheric oxygen levels. Nitrite-oxidizing bacteria ( Nitrobacter sp.) and the dinoflagellate Exuviaella sp. did not produce detectable quantities of N 2O during growth. The results support the view that nitrification is an important source of N 2O in the environment. 相似文献
18.
Microzonation of denitrification was studied in stream sediments by a combined O 2 and N 2O microsensor technique. O 2 and N 2O concentration profiles were recorded simultaneously in intact sediment cores in which C 2H 2 was added to inhibit N 2O reduction in denitrification. The N 2O profiles were used to obtain high-resolution profiles of denitrification activity and NO 3− distribution in the sediments. O 2 penetrated about 1 mm into the dark-incubated sediments, and denitrification was largely restricted to a thin anoxic layer immediately below that. With 115 μM NO 3− in the water phase, denitrification was limited to a narrow zone from 0.7 to 1.4 mm in depth, and total activity was 34 nmol of N cm −2 h −1. With 1,250 μM NO 3− in the water, the denitrification zone was extended to a layer from 0.9 to 4.8 mm in depth, and total activity increased to 124 nmol of N cm −2 h −1. Within most of the activity zone, denitrification was not dependent on the NO 3− concentration and the apparent Km for NO 3− was less than 10 μM. Denitrification was the only NO 3−-consuming process in the dark-incubated stream sediment. Even in the presence of C 2H 2, a significant N 2O reduction (up to 30% of the total N 2O production) occurred in the reduced, NO 3−-free layers below the denitrification zone. This effect must be corrected for during use of the conventional C 2H 2 inhibition technique. 相似文献
19.
Although previous research has demonstrated that NO 3− 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 NO 3− 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 NO 3− and synthetic, high-surface-area goethite. Results showed that the presence of NO 3− 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 NO 3− reduction, a 10-fold decrease in the rate of NO 2− reduction, and a 20-fold increase in the amounts of N 2O produced. Nitrogen stable isotope experiments that utilized δ 15N values of N 2O to distinguish between chemical and biological reduction of NO 2− revealed that the N 2O produced during NO 2− or NO 3− reduction in the presence of goethite was primarily of abiotic origin. These results indicate that concomitant microbial Fe(III) and NO 3− reduction produces NO 2− and Fe(II), which then abiotically react to reduce NO 2− to N 2O with the subsequent oxidation of Fe(II) to Fe(III). 相似文献
20.
The construction of a microsensor which can be used to measure O 2 and N 2O simultaneously is described. The microsensor exhibited a linear response to both O 2 and N 2O, and the response to N 2O was independent of the O 2 concentration and vice versa. The N 2O detection limit of a microsensor with a tip diameter of 20 μm was around 1 μmol liter −1. The signals for O 2 and N 2O were affected by hydrogen sulfide, but other interfering agents were not observed in the biofilms and sediments analyzed. Microprofiles of O 2 and N 2O were measured in a biofilm which was exposed to acetylene to block the N 2O reductase activity of denitrifying bacteria. O 2 penetrated about 0.5 mm into the biofilm and was not affected by acetylene, but the N 2O concentration at 1.4 mm depth increased from 32 to 411 μmol liter −1 after the addition of the inhibitor. The shape of the N 2O profile after the addition of acetylene showed that denitrification (denitrifying activity) was detectable in all anoxic layers of the biofilm. 相似文献
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