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1.
Alfalfa ( Medicago sativa L.) N-sufficient plants were fed 1·5 mM N in the form of NO 3−, NH 4+ or NO 3− in conjunction with NH 4+, or were N-deprived for 2 weeks. The specific activity of phosphoenolpyruvate carboxylase (PEPC) from the non-nodulated roots of N-sufficient plants was increased in comparison with that of N-deprived plants. The PEPC value was highest with NO 3− nutrition, lowest with NH 4+ and intermediate in plants that were fed mixed salts. The protein was more abundant in NO 3−-fed plants than in either NH 4+- or N mixed-fed plants. Nitrogen starvation decreased the level of PEPC mRNA, and nitrate was the N form that most stimulated PEPC gene expression. The malate content was significantly lower in NO 3−-deprived than in NO 3−-sufficient plants. Root malate accumulation was high in NO 3−-fed plants, but decreased significantly in plants that were fed with NH 4+. The effect of malate on the desalted enzyme was also investigated. Root PEPC was not very sensitive to malate and PEPC activity was inhibited only by very high concentrations of malate. Asparagine and glutamine enhanced PEPC activity markedly in NO 3−-fed plants, but failed to affect plants that were either treated with other N types or N starved. Glutamate and citrate inhibited PEPC activity only at optimal pH. N-nutrition also influenced root nitrate and ammonium accumulation. Nitrate accumulated in the roots of NO 3−- and (NO 3− + NH 4+)-fed plants, but was undetectable in those administered NH 4+. Both the nitrate and the ammonium contents were significantly reduced in NO 3−- and (NO 3− + NH 4+)-starved plants. Root accumulation of free amino acids was strongly influenced by the type of N administered. It was highest in NH 4+-fed plants and the most abundant amides were asparagine and glutamine. It was concluded that root PEPC from alfalfa plants is N regulated and that nitrate exerts a strong influence on the PEPC enzyme by enhancing both PEPC gene expression and activity. 相似文献
3.
A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH 4+-N L −1) was considered here. The influent for the Anammox process must be composed of NH 4+-N and NO 2−-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH 4+-N and NO 2−-N at the right stoichiometric ratio. The equal ratio of HCO 3−/NH 4+ in reject water results in a natural pH decrease when approximately 50% of NH 4+ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH 4+-N g −1 volatile suspended solids (VSS) h −1, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day −1 m −3, whereas in the SHARON chemostat was 0.35 kg N day −1 m −3 due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed. 相似文献
4.
In M. braunii, the uptake of NO 3− and NO 2− is blue-light-dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO 2-free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO 3− and NO 2− reductases were active, the pH increased to values of around 10, since the NH 4+ generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H 2SO 4 of NO 3− or NO 2− uptake and reduction showed that two protons were consumed for every one NH 4+ released. The uptake of Cl − was also triggered by blue light with a similar 10 s time response. However, the Cl − -dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl −) taken up by the cells were released to the medium. When the cells lacked NO 3− and NO 2− reductases, the shape of the alkalinization traces in the presence of NO 3− and NO 2− was similar to that in the presence of Cl −, suggesting that NO 3− or NO 2− was also released to the medium. Both the NO 3− and Cl −-dependent rates of alkalinization were independent of mono- and divalent cations. 相似文献
5.
Nitric oxide (NO) is a chemical weapon within the arsenal of immune cells, but is also generated endogenously by different bacteria. Pseudomonas aeruginosa are pathogens that contain an NO-generating nitrite (NO 2−) reductase (NirS), and NO has been shown to influence their virulence. Interestingly, P. aeruginosa also contain NO dioxygenase (Fhp) and nitrate (NO 3−) reductases, which together with NirS provide the potential for NO to be metabolically cycled (NO→NO 3−→NO 2−→NO). Deeper understanding of NO metabolism in P. aeruginosa will increase knowledge of its pathogenesis, and computational models have proven to be useful tools for the quantitative dissection of NO biochemical networks. Here we developed such a model for P. aeruginosa and confirmed its predictive accuracy with measurements of NO, O 2, NO 2−, and NO 3− in mutant cultures devoid of Fhp or NorCB (NO reductase) activity. Using the model, we assessed whether NO was metabolically cycled in aerobic P. aeruginosa cultures. Calculated fluxes indicated a bottleneck at NO 3−, which was relieved upon O 2 depletion. As cell growth depleted dissolved O 2 levels, NO 3− was converted to NO 2− at near-stoichiometric levels, whereas NO 2− consumption did not coincide with NO or NO 3− accumulation. Assimilatory NO 2− reductase (NirBD) or NorCB activity could have prevented NO cycling, and experiments with Δ nirB, Δ nirS, and Δ norC showed that NorCB was responsible for loss of flux from the cycle. Collectively, this work provides a computational tool to analyze NO metabolism in P. aeruginosa, and establishes that P. aeruginosa use NorCB to prevent metabolic cycling of NO. 相似文献
6.
The metabolic capability of denitrifying sludge to oxidize ammonium and p-cresol was evaluated in batch cultures. Ammonium oxidation was studied in presence of nitrite and/or p-cresol by 55 h. At 50 mg/L NH 4+-N and 76 mg/L NO 2−-N, the substrates were consumed at 100% and 95%, respectively, being N 2 the product. At 50 mg/L NH 4+-N and 133 mg/L NO 2−-N, the consumption efficiencies decreased to 96% and 70%, respectively. The increase in nitrite concentration affected the ammonium oxidation rate. Nonetheless, the N 2 production rate did not change. In organotrophic denitrification, the p-cresol oxidation rate was slower than ammonium oxidation. In litho-organotrophic cultures, the p-cresol and ammonium oxidation rates were affected at 133 mg/L NO 2−-N. Nonetheless, at 76 mg/L NO 2−-N the denitrifying sludge oxidized ammonium and p-cresol, but at different rate. Finally, this is the first work reporting the simultaneous oxidation of ammonium and p-cresol with the production of N 2 from denitrifying sludge. 相似文献
7.
The purpose of this work was to evaluate the development of the anammox process by the use of granular sludge selected from
a digestion reactor as a potential seed source in a lab-scale UASB (upflow anaerobic sludge blanket) reactor system. The reactor
was operated for approximately 11 months and was fed by synthetic wastewater. After 200 days of feeding with NH 4
+ and NO 2
− as the main substrates, the biomass showed steady signs of ammonium consumption, resulting in over 60% of ammonium nitrogen
removal. This report aims to present the results and to more closely examine what occurs after the onset of anammox activity,
while the previous work described the start-up experiment and the presence of anammox bacteria in the enriched community using
the fluorescence in situ hybridization (FISH) technique. By the last month of operation, the consumed NO 2
−N/NH 4
+-N ratio in the UASB reactor was close to 1.32, the stoichiometric ratio of the anammox reaction. The obtained results from
the influentshutdown test suggested that nitrite concentration would be one key parameter that promotes the anammox reaction
during the start-up enrichment of anammox bacteria from granular sludge. During the study period, the sludge color gradually
changed from black to red-brownish. 相似文献
8.
Abstract. Nitrate uptake into Chara corallina cells at different external pH (pH o) after different NO 3− pretreatment conditions has been investigated. Following NO 3− pretreatment (0.2 mol m −3 NO 3−) there was little effect of pH o on subsequent net NO 3− uptake into Chara cells. After N deprivation (2 mmol m −3 NO 3−) there was a pronounced effect of pH o on nitrate uptake, the maximum rate occurring at pH o 4.7. There was no consistent relationship between OH − efflux and NO 3− uptake in short term experiments (< 1 h). NO 3− efflux was also sensitive to pH o, the maximum rate occurring at ∼ pH o 5.0. An inhibitor of the proton pump, DES, immediately stimulated NO 3− uptake into cells pretreated with NO 3− and prevented the time-dependent decrease in NO 3−, uptake into Chara cells that had been previously treated with low N (2 mmol m −3 NO 3−). NO 3− efflux was found to be very sensitive to DES with Ki= 0.7 mmol m −3. At the optimum pH o for NO 3− uptake the effect of DES on membrane potential (ψ m) were slight, and only apparent after 30 min. The results are interpreted in context of current models relating NO 3− uptake and H + pump activity. A new model for NO 3− uptake is proposed which involves NO 3−/NO 3− exchange at steady state. 相似文献
9.
Hydrolyzed polyacrylamide (HPAM) biotransformation in an up-flow anaerobic sludge blanket reactor including biodegradation performances, biodegradation mechanisms, key enzymes, and functional microorganisms was explored. Response surface methodology was applied to further improve HPAM degradation. The predicted degradation ratios of HPAM and CODCr were 46.2% and 83.4% under the optimal conditions. HPAM biodegradation ratio and total organic carbon removal ratio reached 40.5% and 38.9%. Total nitrogen concentration was dramatically decreased with the increasing fermentation time during the fermentation, while low ammonia nitrogen (NH4+–N) and nitrite nitrogen (NO2−–N) were generated. NH4+–N and NO2−–N increased slightly on the whole. Enzyme activity change was correlated with HPAM biodegradation. Dehydrogenase activity had a decline of 21.3–41.0%, and the minimum value occurred at 300 mg/L of HPAM. Urease activity was varied from 28.7 to 78.7% and the maximal inhibition ratio occurred at 200 mg/L of HPAM. Mechanisms for the biodegradation of HPAM were also explored by FT-IR, HPLC, and SEM. The results indicated that long-chain HPAM was broken into micromolecule compounds and the amide groups of HPAM were transformed into carboxyl groups. Based on the sequencing results on an Illumina MiSeq platform, Proteobacterias, Bacteroidetes, and Chloroflexi were turned out to be the critical microorganisms involved in HPAM degradation. This work lays a basis for HPAM-containing wastewater treatment and offers a support for water saving and emission reduction. It is of great significance to the sustainable development of oilfield. 相似文献
10.
The effects of inorganic nutrient (ammonium [NH 4 + ] and nitrate [NO 3 − ]) and amino acid (glutamate [glu] and glutamine [gln]) additions on rates of N 2 fixation, N uptake, glutamine synthetase (GS) activity, and concentrations of intracellular pools of gln and glu were examined in natural and cultured populations of Trichodesmium. Additions of 1 μM glu, gln, NO 3 − , or NH 4 + did not affect short-term rates of N 2 fixation. This may be an important factor that allows for continued N 2 fixation in oligotrophic areas where recycling processes are active. N 2 fixation rates decreased when nutrients were supplied at higher concentrations (e.g. 10 μM). Uptake of combined N (NH 4 + , NO 3 − , and amino acids) by Trichodesmium was stimulated by increased concentrations. For NO 3 − , proportional increases in NO 3 − uptake and decreases in N 2 fixation were observed when additions were made to cultures before the onset of the light period. GS activity did not change much in response to the addition of NH 4 + , NO 3 − , glu, or gln. GS is necessary for N metabolism, and the bulk of this enzyme pool may be conserved. Intracellular pools of glu and gln varied in response to 10 μM additions of NH 4 + , glu, or gln. Cells incubated with NH 4 + became depleted in intracellular glu and enriched with intracellular gln. The increase in the gln/glu ratio corresponded to a decrease in the rate of N 2 fixation. Although the gln/glu ratio decreased in cells exposed to the amino acids, there was only a corresponding decrease in N 2 fixation after the gln addition. The results presented here suggest that combined N concentrations on the order of 1 μM do not affect rates of N 2 fixation and metabolism, although higher concentrations (e.g. 10 μM) can. Moreover, these effects are exerted through products of NH 4 + assimilation rather than exogenous N, as has been suggested for other species. These results may help explain how cultures of Trichodesmium are able to simultaneously fix N 2 and take up NH 4 + and how natural populations continue to fix N 2 once combined N concentrations increase within a bloom. 相似文献
11.
The effect of light on BPA degradation by an adapted bacterial consortium was investigated. BPA was completely degraded up to 50 mg l −1, and the degradation followed first-order reaction kinetics both in the light and in the dark. The degradation half-life of BPA when the consortium was grown in presence of light was 21.9, 17.2, and 12.6 h for concentrations of 10, 20, and 50 mg l −1, respectively; the degradation half-life of BPA in the dark was 13.1, 10.8, and 10.2 h for concentrations of 10, 20, and 50 mg l −1, respectively. Therefore, light inhibited BPA biodegradation. However, under both conditions, BPA was completely depleted. The bacterial consortium effectively utilised BPA as a growth substrate to sustain a cell yield of 0.95 g g −1 and 0.97 g g −1 in the light and dark, respectively. A total of ten and nine biodegradation intermediates were detected in the light and dark, respectively. Three bacterial metabolic pathways and one photodegradation pathway were proposed to explain their occurrence. This study demonstrated that bacterial consortia may assemble a wide range of catabolic pathways to allow for efficient degradation of BPA, converting BPA to principally bacterial biomass and metabolites exhibiting low or no oestrogenic activity. 相似文献
12.
Binding of cytoplasmic anionic open channel blockers within the cystic fibrosis transmembrane conductance regulator (CFTR) Cl − channel is antagonized by extracellular Cl −. In the present work, patch clamp recording was used to investigate the interaction between extracellular Cl − (and other anions) and cytoplasmic Pt(NO 2) 42 − ions inside the CFTR channel pore. In constitutively open (E1371Q-CFTR) channels, these different anions bind to two separate sites, located in the outer and inner vestibules of the pore respectively, in a mutually antagonistic fashion. A mutation in the inner vestibule (I344K) that greatly increased Pt(NO 2) 42 − binding affinity also greatly strengthened antagonistic Cl −:blocker interactions as well as the voltage-dependence of block. Quantitative analysis of ion binding affinity suggested that the I344K mutation strengthened interactions not only with intracellular Pt(NO 2) 42 − ions but also with extracellular Cl −, and that altered blocker Cl −- and voltage-dependence were due to the introduction of a novel type of antagonistic ion:ion interaction inside the pore that was independent of Cl − binding in the outer vestibule. It is proposed that this mutation alters the arrangement of anion binding sites inside the pore, allowing both Cl − and Pt(NO 2) 42 − to bind concurrently within the inner vestibule in a strongly mutually antagonistic fashion. However, the I344K mutation does not increase single channel conductance following disruption of Cl − binding in the outer vestibule in R334Q channels. Implications for the arrangement of ion binding sites in the pore, and their functional consequences for blocker binding and for rapid Cl − permeation, are discussed. 相似文献
13.
Nitrite (NO 2−) can accumulate during nitrification in soil following fertilizer application. While the role of NO 2− as a substrate regulating nitrous oxide (N 2O) production is recognized, kinetic data are not available that allow for estimating N 2O production or soil‐to‐atmosphere fluxes as a function of NO 2− levels under aerobic conditions. The current study investigated these kinetics as influenced by soil physical and biochemical factors in soils from cultivated and uncultivated fields in Minnesota, USA. A linear response of N 2O production rate () to NO 2− was observed at concentrations below 60 μg N g −1 soil in both nonsterile and sterilized soils. Rate coefficients ( Kp) relating to NO 2− varied over two orders of magnitude and were correlated with pH, total nitrogen, and soluble and total carbon (C). Total C explained 84% of the variance in Kp across all samples. Abiotic processes accounted for 31–75% of total N 2O production. Biological reduction of NO 2− was enhanced as oxygen (O 2) levels were decreased from above ambient to 5%, consistent with nitrifier denitrification. In contrast, nitrate (NO 3−)‐reduction, and the reduction of N 2O itself, were only stimulated at O 2 levels below 5%. Greater temperature sensitivity was observed for biological compared with chemical N 2O production. Steady‐state model simulations predict that NO 2− levels often found after fertilizer applications have the potential to generate substantial N 2O fluxes even at ambient O 2. This potential derives in part from the production of N 2O under conditions not favorable for N 2O reduction, in contrast to N 2O generated from NO 3− reduction. These results have implications with regard to improved management to minimize agricultural N 2O emissions and improved emissions assessments. 相似文献
14.
ObjectivesTo degrade enzymatically bisphenol A (BPA) that causes serious environmental concerns and is difficult to be degraded by chemical or physical methods.ResultsBPA (150 mg l?1) was completely degraded by chloroperoxidase (CPO)/H2O2 within 7 min at room temperature, atmospheric pressure with the enzyme at 6 μg CPO ml?1. The degradation products were identified by HPLC–MS, which suggested involvement of multiple steps. Enzymatic treatment followed by existing bioremediation technologies (activated sludge) enhanced removal of COD from 9 to 54 %. Using an ecotoxicity evaluation with Chlorella pyrenoidosa, the degradation products had a lower toxicity than BPA.ConclusionBPA can be degraded rapidly and efficiently under mild conditions with chloroperoxidase at 6 μg ml?1. The degradation products had a lower toxicity than BPA. 相似文献
15.
A high-pressure liquid chromatography (HPLC) technique, previously developed for nitrite (NO −2) and nitrate (NO −3) measurements [3], was used to measure chlorite (ClO −2) production by Nitrobacter winogradskyi. The determination of ClO −2 by HPLC involves monitoring the column effluent with a UV detector at 214 or 254 nm. Although the absorbance of ClO −2 at 214 nm was about 5 times greater than at 254 nm, interference from other compounds in the culture filtrates of N. winogradskyi contributed to an unstable detector signal. The detection limit at 254 nm for ClO −2 in deionized water was about 1 μM.The measurement of ClO −2 in N. winogradskyi culture filtrates was done with detection at 254 nm. The maximum concentration of ClO −2 produced by anaerobically incubated cell suspensions of N. winogradskyi was about 80 μM. 相似文献
16.
The effect of NH 4+/NO 3− availability on nitrate reductase (NR) activity in Phragmites australis and Glyceria maxima was studied in sand and water cultures with the goal to characterise the relationship between NR activity and NO 3− availability in the rhizosphere and to describe the extent to which NH 4+ suppresses the utilization of NO 3− in wetland plants.The NR activity data showed that both wetland helophytes are able to utilize NO 3−. This finding was further supported by sufficient growth observed under the strict NO 3− nutrition. The distribution of NR activity within plant tissues differed between species. Phragmites was proved to be preferential leaf NO 3− reducer with high NR activity in leaves (NR max > 6.5 μmol NO 2− g dry wt −1 h −1) under all N treatments, and therefore Phragmites seems to be good indicator of NO 3− availability in flooded sediment. In the case of Glyceria the contribution of roots to plant NO 3− reduction was higher, especially in sand culture. Glyceria also tended to accumulate NO 3− in non-reduced form, showing generally lower leaf NR activity levels. Thus, the NR activity does not necessarily correspond with plant ability to take up NO 3− and grow under NO 3−-N source. Moreover, the species differed significantly in the content of compounds interfering with NR activity estimation. Glyceria, but not Phragmites, contained cyanogenic glycosides releasing cyanide, the potent NR inhibitor. It clearly shows that the use of NR activity as a marker of NO 3− utilization in individual plant species is impossible without the precise method optimisation. 相似文献
17.
In this environmental-sample based study, rapid microbial-mediated degradation of 2,4,6-trinitrotoluene (TNT) contaminated soils is demonstrated by a novel strain, Achromobacter spanius STE 11. Complete removal of 100 mg L −1 TNT is achieved within only 20 h under aerobic conditions by the isolate. In this bio-conversion process, TNT is transformed to 2,4-dinitrotoluene (7 mg L −1), 2,6-dinitrotoluene (3 mg L −1), 4-aminodinitrotoluene (49 mg L −1) and 2-aminodinitrotoluene (16 mg L −1) as the key metabolites. A. spanius STE 11 has the ability to denitrate TNT in aerobic conditions as suggested by the dinitrotoluene and NO 3 productions during the growth period. Elemental analysis results indicate that 24.77 mg L −1 nitrogen from TNT was accumulated in the cell biomass, showing that STE 11 can use TNT as its sole nitrogen source. TNT degradation was observed between pH 4.0–8.0 and 4–43 °C; however, the most efficient degradation was at pH 6.0–7.0 and 30 °C. 相似文献
18.
Electrocatalytic nitrite (NO 2−) reduction reaction (NO 2−RR) for ammonia (NH 3) synthesis is a promising alternative for NO 2− resource utilization. Herein, a dual-site copper-cobalt oxide catalyst is reported for the efficient electrocatalytic reduction of NO 2− to NH 3, exhibiting NH 3 Faradaic efficiency that remained above 95% (0.1 m NaNO 2) over a wide potential window (−0.1 to −0.6 V vs reversible hydrogen electrode, vs RHE). More importantly, the high NH 3 Faradaic efficiency maintains an over 85% (−0.1 to −0.3 V vs RHE) at a low concentration of NaNO 2 (0.01 m ). Theoretical calculations demonstrate that CuO serves the *NO 2 to *NO and is subsequently converted to NH 3 on Co 3O 4. Coupled anodic ethylene glycol (EG) oxidation reaction endows low cell voltage (ΔU = 480 mV, 10 mA cm −2) and energy consumption saving (>23%) in a two-electrode system. This work provides a reference for a co-upcycling electrolyzer for NO 2− and EG. 相似文献
19.
Developing an effective method for the detection of nitrite (NO 2−) ions in the natural environment especially in environmental waters and soils is very necessary, since they will cause serious damage to human health once excess NO 2− ions enters the human body. Therefore, a new colorimetric fluorescent probe NB-NO 2− for determining NO 2− ions was designed, which possesses good water-solubility and satisfactory selectivity over other common ions for NO 2− ions. The addition of NO 2− ions changed the color of solution from blue to colorless seen by the naked-eye. Furthermore, through test and calculation, the detection limit of the probe NB-NO 2− is 129 nM. Based on the earlier excellent characteristics, the probe NB-NO 2− was successfully used for monitoring NO 2− ions in environmental waters and soils. 相似文献
20.
A gap in our understanding of the beneficial systemic responses to dietary constituents nitrate (NO 3−), nitrite (NO 2−) and conjugated linoleic acid (cLA) is the identification of the downstream metabolites that mediate their actions. To examine these reactions in a clinical context, investigational drug preparations of 15N-labeled NO 3− and NO 2− were orally administered to healthy humans with and without cLA. Mass spectrometry analysis of plasma and urine indicated that the nitrating species nitrogen dioxide was formed and reacted with the olefinic carbons of unsaturated fatty acids to yield the electrophilic fatty acid, nitro-cLA (NO 2-cLA). These species mediate the post-translational modification (PTM) of proteins via reversible Michael addition with nucleophilic amino acids. The PTM of critical target proteins by electrophilic lipids has been described as a sensing mechanism that regulates adaptive cellular responses, but little is known about the endogenous generation of fatty acid nitroalkenes and their metabolites. We report that healthy humans consuming 15N-labeled NO 3− or NO 2−, with and without cLA supplementation, produce 15NO 2-cLA and corresponding metabolites that are detected in plasma and urine. These data support that the dietary constituents NO 3−, NO 2- and cLA promote the further generation of secondary electrophilic lipid products that are absorbed into the circulation at concentrations sufficient to exert systemic effects before being catabolized or excreted. 相似文献
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