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1.
Despite its ecological importance, essential aspects of microbial N2O reduction—such as the effect of O2 availability on the N2O sink capacity of a community—remain unclear. We studied N2O vs. aerobic respiration in a chemostat culture to explore (i) the extent to which simultaneous respiration of N2O and O2 can occur, (ii) the mechanism governing the competition for N2O and O2, and (iii) how the N2O-reducing capacity of a community is affected by dynamic oxic/anoxic shifts such as those that may occur during nitrogen removal in wastewater treatment systems. Despite its prolonged growth and enrichment with N2O as the sole electron acceptor, the culture readily switched to aerobic respiration upon exposure to O2. When supplied simultaneously, N2O reduction to N2 was only detected when the O2 concentration was limiting the respiration rate. The biomass yields per electron accepted during growth on N2O are in agreement with our current knowledge of electron transport chain biochemistry in model denitrifiers like Paracoccus denitrificans. The culture’s affinity constant (KS) for O2 was found to be two orders of magnitude lower than the value for N2O, explaining the preferential use of O2 over N2O under most environmentally relevant conditions. 相似文献
2.
Understanding of N 2O fluxes to the atmosphere is complicated by interactions between chemical and physical controls on both production and movement of the gas. To better understand how N 2O production is controlled in the soil, we measured concentrations of N 2O and of the proximal controllers on its production in soil water and soil air in a field study in the Rio Icacos basin of the Luquillo Experimental Forest, Puerto Rico. A toposequence (ridge, slope-ridge break, slope, slope-riparian break, riparian, and streambank) was used that has been previously characterized for groundwater chemistry and surface N 2O fluxes. The proximal controls on N 2O production include NO 3
–, NH 4
+, DOC, and O 2. Nitrous oxide and O 2 were measured in soil air and NO 3
–, NH 4
+, and DO were measured in soil water. Nitrate and DOC disappeared from soil solution at the slope-riparian interface, where soil N 2O concentrations increased dramatically. Soil N 2O concentrations continued to increase through the flood plain and the streambank. Nitrous oxide concentrations were highest in soil air probes that had intermediate O 2 concentrations. Changes in N 2O concentrations in groundwater and soil air in different environments along the catena appear to be controlled by O 2 concentrations. In general, N processing in the unsaturated and saturated zones differs within each topographic position apparently due to differences in redox status. 相似文献
3.
A conventional Clark-type O 2 probe was used to determine N 2O concentrations in suspensions. At a polarizing voltage of–0.95 V versus the reference Ag/AgCl electrode, the probe is almost half as sensitive for N 2O as for O 2, and the detection limit is less than 1 M N 2O. The probe can also be used to determine NO for which the suitable polarizing voltage is–0.7 V. The method was successfully applied for continuously recording dissimilatory formation or utilization of N 2O by intact Azospirillum brasilense Sp 7, NO production by extracts from this bacterium, and N 2O reduction catalyzed by nitrogenase in intact Klebsiella pneumoniae. It is concluded that the probe is useful for measuring N 2O or NO contents in bacterial suspensions when the O 2 level is zero or kept constant during the assays. 相似文献
4.
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
5.
The availability of O 2 is believed to be one of the main factors regulating nitrification and denitrification and the release of NO and N 2O. The availability of O 2 in soil is controlled by the O 2 partial pressure in the gas phase and by the moisture content in the soil. Therefore, we investigated the influence of O 2 partial pressures and soil moisture contents on the NO and N 2O release in a sandy and a loamy silt and differentiated between nitrification and denitrification by selective inhibition of nitrification with 10 Pa acetylene. At 60% whc (maximum water holding capacity) NO and N 2O release by denitrification increased with decreasing O 2 partial pressure and reached a maximum under anoxic conditions. Under anoxic conditions NO and N 2O were only released by denitrification. NO and N 2O release by nitrification also increased with decreasing O 2 partial pressure, but reached a maximum at 0.1–0.5% O 2 and then decreased again. Nitrification was the main source of NO and N 2O at O 2 partial pressures higher than 0.1–0.5% O 2. At lower O 2 partial pressures denitrification was the main source of NO and N 2O. With decreasing O 2 partial pressure N 2O release increased more than NO release, indicating that the N 2O release was more sensitive against O 2 than the NO release. At ambient O 2 partial pressure (20.5% O 2) NO and N 2O release by denitrification increased with increasing soil moisture content. The maximum NO and N 2O release was observed at soil moisture contents of 65–80% whc and 100% whc, respectively. NO and N 2O release by nitrification also increased with increasing soil moisture content with a maximum at 45–55% whc and 90% whc, respectively. Nitrification was the main source of NO and N 2O at soil moisture contents lower than 90% whc and 80% whc, respectively. Higher soil moisture contents favoured NO and N 2O release by denitrification. Soil texture had also an effect on the release of NO and N 2O. The coarse-textured sandy silt released more NO than N 2O compared with the fine-textured loamy silt. At high soil moisture contents (80–100% whc) the fine-textured soil showed a higher N 2O release by denitrification than the coarse-textured soil. We assume that the fine-textured soil became anoxic at a lower soil moisture content than the coarse-textured soil. In conclusion, the effects of O 2 partial pressure, soil moisture and soil texture were consistent with the theory that denitrification increasingly contributes to the release of NO and in particular N 2O when conditions for soil microorganisms become increasingly anoxic. 相似文献
6.
It has been shown both theoretically and experimentally that interphase nitrogen transport may have a significant influence on the rate of interphase oxygen transport, and thereby also on the value of the volumetric mass transfer coefficient of oxygen, kla, determined in mechanically agitated bubble fermentors using the variants of dynamic method presented in the literature. The experiments were carried out in 1 M KCI solution at five stirrer frequencies and two gas inlet levels. The gas interchanges were performed either without interrupting the aeration and agitation of the charge (A) or with the aeration and agitation of the charge turned on at the same time (B). The applied variants of the interchange were N 2→ O 2→, O 2→ N 2, N 2→ air, air→ N 2, O→ O 2, and O→ air. In the two last variants the oxygen dissolved in the charge was removed by reacting with sulfite ions. The kla values calculated by allowing for the nitrogen transport for procedure A were approximately equal to the values obtained by disregarding the nitrogen transport, whereas those for procedure B were higher (up to 40%), than the values obtained disregarding the nitrogen transport. 相似文献
7.
The dependence of sensitivity of an explosive on its molecular structure may be mainly attributed to the molecular deformability, which can be expressed by some characteristic parameters, resonance energy for aromatic an explosive, strain energy for a strained-ring or strained-cage explosive, large π-π separation energy for a large π-π linked-explosive, bond rotational energy barriers of C–NO2, N–NO2, O–NO2 for C–NO2, N–NO2, O–NO2 bond-based explosives, and so on. Molecular polarizability of an explosive is also an important molecular deformability index, which can be effectively used to compare impact sensitivities of explosive’s isomers, isoelectronic species, and similar structures. Interestingly, comparing the molecular polarizabilities under external electric fields with different energy levels of isomeric N20(Ih) and N20(D3d) clusters and the Mo2N20 and Re2N20 complex compounds, it is found that there are different energy thresholds of significant molecular expansion. 相似文献
8.
We modified and tuned a commercial model of a gas chromatography/mass spectrometry (GC/MS) instrument to develop a simple and rapid method for the simultaneous quantification of a variety of gas species. Using the developed method with the newly modified instrument, gas species such as H 2, N 2, O 2, CO, NO, CH 4, CO 2, and N 2O, which are common components of microbial metabolism, were accurately identified based on their retention times and/or mass-to-charge ratios (m/z) in less than 2.5 min. By examining the sensitivities and dynamic ranges for the detection of H 2, N 2, O 2, CH 4, CO 2, and N 2O, it was demonstrated that the method developed in this study was sufficient for accurately monitoring the production and the consumption of these gaseous species during microbial metabolism. The utility of the new method was demonstrated by a denitrification study with Pseudomonas aureofaciens ATCC 13985 T. This method will be suitable for a variety of applications requiring the identification of gaseous metabolites in microorganisms, microbial communities, and natural ecosystems. 相似文献
9.
Lorazepam and oxazepam in plasma and urine were measued by gas chromatography—mass spectrometry. Oxazepam was used as an internal standard in the assay of lorazepam and vice versa. After removal of interfering substances with n-hexane, the drugs were extracted with benzene and converted to N 1,O 3-bistrimethylsilyl derivatives. Glucuronide forms of the drugs were extracted after hydrolysis with β-glucuronidase. A common fragment ion at m/e 429 was used to monitor the two drugs. The sensitivity was 2 ng/ml for both drugs, which was sufficient to determine plasma and urine concentrations after therapeutic doses to humans. 相似文献
10.
Background and aims Elevated atmospheric CO 2 ( eCO 2) and tropospheric O 3 ( eO 3) can alter soil microbial processes, including those underlying N 2O emissions, as an indirect result of changes in plant inputs. In this study, effects of eCO 2 and eO 3 on sources of N 2O in a soybean ( Glycine max (L.) Merr.) agroecosystem in Illinois (SoyFACE) were investigated. We hypothesized that increases in available C and anaerobic microhabitat under eCO 2 would stimulate N 2O emissions, with a proportionally larger increase in denitrification derived N 2O (N 2O D) compared to nitrification plus nitrifier denitrification derived N 2O (N 2O N+ND). We expected opposite effects under eO 3. Methods Isotopically labeled 15NH 4 14 NO 3 and 14NH 4 15 NO 3 were used to evaluate mineral N transformations, N 2O D, and N 2O N+ND in a 12-day incubation experiment. Results We observed minimal effects of eCO 2 and eO 3 on N 2O emissions, movement of 15?N through mineral N pools, soil moisture content and C availability. Possibly, altered C and N inputs by eCO 2 and eO 3 were small relative to the high soil organic C content and N-inputs via biological N 2-fixation, minimizing potential effects of eCO 2 and eO 3 on N-cycling. Conclusion We conclude that eCO 2 and eO 3 did not affect N 2O emissions in the short term. However, it remains to be tested whether N 2O emissions in SoyFACE will be unaltered by eCO 2 and eO 3 on a larger temporal scale under field conditions. 相似文献
11.
The effect of mild hypoxic hypoxia on brain metabolism and acetylcholine synthesis was studied in awake, restrained rats. Since many studies of hypoxia are done with animals anesthetized with nitrous oxide (N 2O), the effects of N 2O were evaluated. N 2O (70%) increased the cerebral cortical blood flow by 33% and the cortical metabolic rate of oxygen by 26%. In addition, the synthesis of acetylcholine in N 2O-anesthetized animals, measured with [U- 14C]glucose and [1- 2H 2,2- 2H 2]choline, decreased by 45 and 53%, respectively. Consequently, mild hypoxia was studied in unanesthetized rats. Control rats breathing 30% O 2 (partial pressure of oxygen, Pao 2= 120 mm Hg) were compared with rats exposed to 15% O 2 (Pao 2= 57 mm Hg) or 10% O 2 (Pao 2= 42 mm Hg). The synthesis of acetylcholine, measured with [U- 14C]glucose, was decreased by 35 and 54% with 15% O 2 and 10% O 2 respectively; acetylcholine synthesis, measured with [1- 2H 2,2- 2H 2]choline, was decreased by 50 and 68% with 15% O 2 and 10% O 2 respectively. Animals breathing either 15% or 10% O 2 had normal cerebral metabolic rates of oxygen but had increased brain lactates and increased cortical blood flows compared with animals breathing 30% O 2. These results show that even mild hypoxic hypoxia impairs acetylcholine synthesis, which in turn may account for the early symptoms of brain dysfunction associated with hypoxia. 相似文献
12.
Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N 2O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in situ studies to elucidate the key factors controlling soil N 2O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N 2O fluxes in an arable soil, combined with in situ high-frequency measurements of soil matrix oxygen (O 2) and N 2O concentrations, in situ 15N labeling, and N 2O 15N site preference (SP). The in situ O 2 concentration and further microcosm visualized spatiotemporal distribution of O 2 both suggested that O 2 dynamics were the proximal determining factor to matrix N 2O concentration and fluxes due to quick O 2 depletion after N fertilization. Further SP analysis and in situ 15N labeling experiment revealed that the main source for N 2O emissions was bacterial denitrification during the hot-wet summer with lower soil O 2 concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold-dry winter with higher soil O 2 concentration. The robust positive correlation between O 2 concentration and SP values underpinned that the O 2 dynamics were the key factor to differentiate the composite processes of N 2O production in in situ structured soil. Our findings deciphered the complexity of N 2O production processes in real field conditions, and suggest that O 2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N 2O production processes in undisturbed structure soils. Our results help to develop targeted N 2O mitigation measures and to improve process models for constraining global N 2O budget. 相似文献
13.
Wastewater treatment plants are known to be important point sources for nitrous oxide (N 2O) in the anthropogenic N cycle. Biofilm based treatment systems have gained increasing popularity in the treatment of wastewater, but the mechanisms and controls of N 2O formation are not fully understood. Here, we review functional groups of microorganism involved in nitrogen (N) transformations during wastewater treatment, with emphasis on potential mechanism of N 2O production in biofilms. Biofilms used in wastewater treatment typically harbour aerobic and anaerobic zones, mediating close interactions between different groups of N transforming organisms. Current models of mass transfer and biomass interactions in biofilms are discussed to illustrate the complex regulation of N 2O production. Ammonia oxidizing bacteria (AOB) are the prime source for N 2O in aerobic zones, while heterotrophic denitrifiers dominate N 2O production in anoxic zones. Nitrosative stress ensuing from accumulation of NO 2 ? during partial nitrification or denitrification seems to be one of the most critical factors for enhanced N 2O formation. In AOB, N 2O production is coupled to nitrifier denitrification triggered by nitrosative stress, low O 2 tension or low pH. Chemical N 2O production from AOB intermediates (NH 2OH, HNO, NO) released during high NH 3 turnover seems to be limited to surface-near AOB clusters, since diffusive mass transport resistance for O 2 slows down NH 3 oxidation rates in deeper biofilm layers. The proportion of N 2O among gaseous intermediates (NO, N 2O, N 2) in heterotrophic denitrification increases when NO or nitrous acid (HNO 2) accumulates because of increasing NO 2 ?, or when transient oxygen intrusion impairs complete denitrification. Limited electron donor availability due to mass transport limitation of organic substrates into anoxic biofilm zones is another important factor supporting high N 2O/N 2 ratios in heterotrophic denitrifiers. Biofilms accommodating Anammox bacteria release less N 2O, because Anammox bacteria have no known N 2O producing metabolism and reduce NO 2 ? to N 2, thereby lowering nitrosative stress to AOB and heterotrophs. 相似文献
14.
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
15.
Rivers are important sources of N 2O emissions into the atmosphere. Nevertheless, N 2O production processes in rivers are not well identified. We measured concentrations and isotopic ratios of N 2O, NH 4 +, NO 2 ?, and NO 3 ? in surface water to identify the microbial processes of N 2O production along the Tama River in Japan. We also measured the functional gene abundance of nitrifiers and denitrifiers ( amoA-bacteria, nirK, nirS, nosZ clade I, nosZ clade II) together with concentrations of dissolved organic carbon (DOC) and fluorescence intensities of protein and humic components of dissolved organic matter (DOM) to support the elucidation of N 2O production processes. The observed nitrogen (δ 15N) and oxygen (δ 18O) of N 2O were within the expected isotopic range of N 2O produced by nitrate reduction, indicating that N 2O was dominantly produced by denitrification. The positive significant correlation between N 2O Net concentration and nirK gene abundance implied that nitrifiers and denitrifiers are contributors to N 2O production. Fluorescence intensities of protein and humic components of DOM and concentrations of DOC did not show significant correlations with N 2O concentrations, which suggests that DOC and abundance of DOM components do not control dissolved N 2O. Measurement of isotope ratios of N 2O and its substrates was found to be a useful tool to obtain evidence of denitrification as the main source of N 2O production along the Tama River. 相似文献
16.
Net productions of permanent soil atmosphere gases (N 2, CO 2, O 2) and temporary gases (N 2O, NO) were monitored in soil cores using a non-interfering, fully automated measuring technique allowing highly time resolved measurements over prolonged periods. The influence of changes in available organic carbon on CO 2, N 2O, NO and N 2 production was studied by changing the soil carbon content through aerobic preincubations of different length, up to 21 days.The aerobic preincubation caused an increase in NO 3
- concentration and a decrease in available carbon content. Available carbon content dominated both CO 2 and total N gas (N 2+N 2O+NO) production during anaerobiosis. Both CO 2 and total N gas production rates decreased with increasing length of the previous aerobic preincubation, this in spite of the higher initial NO 3
- concentration.Total denitrification rates were closely related to the anaerobic CO 2 production rates. No relation was found between water soluble carbon content and total denitrification. The N 2O/N 2 ratio could be explained by an interaction of carbon availability, NO 3
- concentration and enzyme status. Net N 2O consumption was monitored. The balance between cumulative total N gas production and NO 3
- consumption varied according to the different treatments. Cumulative N 2O production exceeded cumulative N 2 production for 0 up to 5 days. 相似文献
17.
Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4- N, N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4- N, N-dimethylaminobenzoate-κO)(μ2–4- N, N-dimethylaminobenzoic acid-κO)(4- N, N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La 2O 3 nanomaterials to obtain a nanohybrid La 2O 3/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La 2O 3/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La 2O 3/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour. 相似文献
18.
The complex μ-3,3′-[1,2-ethanediyl-bis(nitrilome- thylidyne)-bis(2-hydroxybenzoato)] aquadicopper(II) hydrate, C 18H 16N 2O 8Cu 2, was isolated from an attempted preparation of a copper lanthanum binuclear complex. The dark purple crystals are monoclinic, space group P2 1/ n, with 4 molecules per unit cell; dimensions a = 13.961(5), b = tl.787(3), c = 11.622(3) Å and β = 113.09(2)°. The final R was 0.046 for the 2062 reflections used in the analysis. The Cu atom in the N 2O 2 cavity is five coordinate with CuN distances of 1.879 and 1.880 Å and CuO distances of 1.898 and 1.900 Å. A water molecule at 2.557 Å completes the square pyramidal arrangement. The second Cu in the O 4 cavity is square planar, with CuO distances to the bridging oxygens of 1.914 and 1.909 Å and to the carboxy oxygens of 1.871 and 1.882 Å. A survey of copper complexes in a square planar N 2O 2 arrangement has led to the equation δCu from the N 2O 2 plane = 0.822 – 0.275 (CuO axial distance) with a correlation coefficient of 0.98 for the 12 structures in which the Cu atom is bonded to a fifth oxygen atom. A model for the transition from square planar to square pyramidal geometry is proposed. 相似文献
19.
The ocean is a net source of N 2O, a potent greenhouse gas and ozone-depleting agent. However, the removal of N 2O via microbial N 2O consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand N 2O consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O 2 tolerance, and community composition of N 2O-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ N 2O production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting N 2O cycling. Microbes from the oxic layer consume N 2O under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that N 2O consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O 2 and N 2O gradients right above the ODZ is a previously ignored potential gatekeeper of N 2O and should be accounted for in the marine N 2O budget.Subject terms: Water microbiology, Biogeochemistry, Microbial ecology 相似文献
20.
Electrochemical and spectroelectrochemical (UV-Vis, IR, EPR) of pd (pd = 1,10-phenanthroline-5,6-dione), Pt( N, N′-pd)Cl2, Pd( N, N′-pd)Cl 2, [Ru(bpy) 2( N, N′-pd)]Cl 2 (bpy = 2,2′-bipyridine) and Pt( O, O′-pd)(PPh 3) 2, where N, N′ and O, O′ refers to coordination of pd to the metal centre via N and O atoms, respectively, reveals that the electron transfer processes between +0.5 and −1.25 V all occur at the pd ligand in agreement with DFT calculations. The two CO groups carry a significant amount of the negative charge in mono-reduced pd 1−. The mode of coordination of pd has a greater influence on its redox chemistry than the metal centre or the ancillary ligands. 相似文献
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