Showing papers on "Nitrite published in 1998"

Photochemical Formation of Hydroxyl Radical by Constituents of Natural Waters

Abstract: A new method is employed to determine the rates of photochemical hydroxyl radical (OH) formation in aqueous solutions and in natural waters under both aerobic and anaerobic conditions. Quantum yields for OH formation from the photolysis of nitrate and nitrite obtained by this method are in good agreement with previous measurements. Photolysis of Suwannee River fulvic acid (SRFA) solutions produced the hydroxyl radical under anaerobic conditions in proportion to the SRFA concentration. Under aerobic conditions, the quantum yields for OH formation were slightly higher and exhibited a different wavelength dependence than those obtained under anaerobic conditions. Experiments employing catalase indicate that Fenton chemistry can account for at most 50% of the total signal under aerobic conditions for SRFA irradiated at 310 and 320 nm. These results indicate the presence of a dioxygen-independent pathway of hydroxyl radical production that cannot be assigned to nitrate/nitrite photolysis or to Fenton chemistry...

Semiautomated Measurement of Nitrate in Biological Fluids

Abstract: The nitric oxide radical (NO·) plays an important role as a physiological messenger (1). NO is formed from l-arginine (2) by NO synthase (NOS; EC 1.14.13.39), which exists in several isoforms (3). Constitutive calcium-dependent isoforms (cNOS) modulate the control of vascular tone in endothelial cells or the neurotransmission in neurons, whereas inducible calcium-independent isoforms (iNOS) are located in macrophages, chondrocytes, and hepatocytes and are induced by cytokines and endotoxin (4)(5). Pathological conditions associated with increased release of cytokines and endotoxin, e.g., inflammation or sepsis (6), can therefore increase NO production. NO is a very unstable, short half-life gas that breaks down rapidly into the stable products nitrate and nitrite (7). Upon coming into the bloodstream, nitrite reacts immediately with oxyhemoglobin to form methemoglobin. Consequently, most NO produced is detected in serum as the remaining product, nitrate (8). Recently, several reports focused on methods to measure nitrate concentrations in biological fluids (9)(10)(11). One of the most commonly used methods is based on the reduction of nitrate to nitrite by cadmium or nitrate reductase, the nitrite produced being determined by Griess reaction (9)(12)(13). Other methods for monitoring NO production are based on chemiluminescence (11)(14), enzymatic assay with an internal standard (10), or chromatographic procedures (8) for nitrate (15)—all of which are time-consuming for routine application in clinical chemistry laboratories. We describe a rapid semiautomated method based on the Griess reaction, involving a shortened incubation period of nitrate with cadmium. The method is applicable to several types of biological fluids. Serum or plasma samples from healthy individuals after a 12-h fast were obtained in accordance with the Medical Ethical Committee of our hospital. Samples were stored at −20 °C and were stable for at least 6 months. The method was …

Effects of pH and Oxygen and Ammonium Concentrations on the Community Structure of Nitrifying Bacteria from Wastewater

Abstract: Autotrophic nitrifying bacteria that oxidize ammonium to nitrite and nitrate are found in soils, sediments, wastewaters, freshwater, and marine water and on building facades. They are essential components of the nitrogen (N) cycle, linking the most reduced and most oxidized forms of inorganic N. Nitrification occurs as a two-step process carried out by two distinct groups of bacteria; ammonia-oxidizing bacteria convert ammonia to nitrite, and then nitrite oxidizers convert nitrite to nitrate (22, 30). Environmental factors control the rate of nitrification. The most significant environmental factors are substrate concentration, pH, temperature, and oxygen availability (12, 23). Nitrifying bacteria exhibit different substrate concentration sensitivities (26). Media containing low substrate concentrations (10 mg of NH4+ liter−1) can give larger most-probable-number counts of ammonia oxidizers than media containing higher NH4+ concentrations (6, 26). Also, ammonia oxidation is inhibited at high substrate concentrations. The growth rates of Nitrosomonas spp. cultures were reduced in the presence of 1,050 to 2,800 mg of NH4+-N liter−1 (16). Substrate inhibition of ammonia oxidation has also been observed in studies of wastewater systems (23). Natural environments, such as soil and water, usually contain 1 to 10 mg of NH4+-N liter−1 (22), yet liquid wastes from animal farms give rise to concentrations up to 1,600 or 5,600 mg of NH4+-N liter−1 (5, 17). Free ammonia (NH3) rather than the total ammonium concentration inhibits ammonia oxidizers (1). As the ratio between the ionized form and the nonionized form depends on pH, the toxicity of ammonium also depends on the environmental pH. The pH range for growth of pure cultures of ammonia oxidizers is 5.8 to 8.5, and the pH range for growth of nitrite oxidizers is 6.5 to 8.5 (30). Nitrification was inhibited at pH values below 5.8 in our preliminary experiments performed with an enriched culture of nitrifiers obtained from wastewater. Yet in natural environments, such as soil, nitrification has been reported to occur at pH values below 4.0 (7, 29). Limiting amounts of dissolved oxygen (concentrations below 2 mg liter−1) inhibit nitrification and cause nitrite accumulation or nitrous and nitric oxide production (9, 21). Ammonia-oxidizing bacteria are the key functional group in removing ammonium from wastewaters. Knowledge of the effect of oxygen on nitrification and nitrifying populations has economic importance since aeration of activated sludge is one of the most costly items in the operation of a wastewater treatment plant (21). In environments with high inputs of ammonium, such as wastewaters, biooxidation of this substrate increases the oxygen uptake and lowers the pH. Such modifications of the environment not only affect the production of nitrite and nitrate but can also select a different nitrifying community that is perhaps specialized for these new conditions. Nitrification does occur in extreme environments that pure cultures of nitrifiers cannot tolerate (4). In this study we examined extreme environments in which nitrifying bacteria may be viable but have not been cultured thus far. Because of the difficulty of obtaining nitrifier isolates, nucleic acid-based methods have greatly aided studies of the diversity of nitrifiers (11, 20, 27, 28). Recent molecular investigations have provided valuable information concerning the diversity of ammonia oxidizers in natural environments (5, 15, 20, 25). However, no previous study has focused on the structural or compositional responses of nitrifying communities to perturbations in the environment. In the present laboratory study we examined the effects of high ammonium concentrations, different pH values, and different oxygen concentrations on nitrification and on the community structure of nitrifying bacteria from wastewater. To test the abilities of the communities to regain their original structures, growth of nitrifying communities under the new conditions was followed by incubation under the original conditions.

Nitrotyrosine-protein adducts in hepatic centrilobular areas following toxic doses of acetaminophen in mice.

Abstract: Treatment of mice with a toxic dose of acetaminophen (300 mg/kg, ip) significantly increased hepatotoxicity at 4 h, as evidenced by histological necrosis in the centrilobular areas of the liver, and increased serum levels of alanine aminotransferase (ALT) (from 8 ± 1 IU/L in saline-treated mice to 3226 ± 892 IU/L in the acetaminophen-treated mice). Serum levels of nitrate plus nitrite (a marker of nitric oxide synthesis) were also increased from 62 ± 8 μM in saline-treated mice to 110 ± 14 μM in acetaminophen-treated mice (P < 0.05). Regression analysis of serum ALT levels to serum nitrate plus nitrite levels in individual mice revealed a positive, linear relationship between serum ALT levels and serum nitrate plus nitrite levels with a correlation coefficient of 0.9 (P < 0.05). The y intercept value (nitrate plus nitrite level) was 63 ± 15 μM. Immunohistochemical analysis of liver sections from acetaminophen-intoxicated mice using an anti-3-nitrotyrosine antibody indicated tyrosine nitration in the prote...

Loss of Ammonia Monooxygenase Activity in Nitrosomonas europaea upon Exposure to Nitrite

Abstract: Nitrosomonas europaea, an obligate ammonia-oxidizing bacterium, lost an increasing amount of ammonia oxidation activity upon exposure to increasing concentrations of nitrite, the primary product of ammonia-oxidizing metabolism. The loss of activity was specific to the ammonia monooxygenase (AMO) enzyme, as confirmed by a decreased rate of NH4+-dependent O2 consumption, some loss of active AMO molecules observed by polypeptide labeling with 14C2H2, the protection of activity by substrates of AMO, and the requirement for copper. The loss of AMO activity via nitrite occurred under both aerobic and anaerobic conditions, and more activity was lost under alkaline than under acidic conditions except in the presence of large concentrations (20 mM) of nitrite. These results indicate that nitrite toxicity in N. europaea is mediated by a unique mechanism that is specific for AMO.

A two-component monooxygenase catalyzes both the hydroxylation of p-nitrophenol and the oxidative release of nitrite from 4-nitrocatechol in Bacillus sphaericus JS905

Abstract: Bacteria that metabolize p-nitrophenol (PNP) oxidize the substrate to 3-ketoadipic acid via either hydroquinone or 1,2,4-trihydroxybenzene (THB); however, initial steps in the pathway for PNP biodegradation via THB are unclear The product of initial hydroxylation of PNP could be either 4-nitrocatechol or 4-nitroresorcinol Here we describe the complete pathway for aerobic PNP degradation by Bacillus sphaericus JS905 that was isolated by selective enrichment from an agricultural soil in India Washed cells of PNP-grown JS905 released nitrite in stoichiometric amounts from PNP and 4-nitrocatechol Experiments with extracts obtained from PNP-grown cells revealed that the initial reaction is a hydroxylation of PNP to yield 4-nitrocatechol 4-Nitrocatechol is subsequently oxidized to THB with the concomitant removal of the nitro group as nitrite The enzyme that catalyzed the two sequential monooxygenations of PNP was partially purified and separated into two components by anion-exchange chromatography and size exclusion chromatography Both components were required for NADH-dependent oxidative release of nitrite from PNP or 4-nitrocatechol One of the components was identified as a reductase based on its ability to catalyze the NAD(P)H-dependent reduction of 2,6-dichlorophenolindophenol and nitroblue tetrazolium Nitrite release from either PNP or 4-nitrocatechol was inhibited by the flavoprotein inhibitor methimazole Our results indicate that the two monooxygenations of PNP to THB are catalyzed by a single two-component enzyme system comprising a flavoprotein reductase and an oxygenase

Nitrite levels in breath condensate of patients with cystic fibrosis is elevated in contrast to exhaled nitric oxide

Abstract: BACKGROUND: Nitric oxide (NO) is released by activated macrophages, neutrophils, and stimulated bronchial epithelial cells. Exhaled NO has been shown to be increased in patients with asthma and has been put forward as a marker of airways inflammation. However, we have found that exhaled NO is not raised in patients with cystic fibrosis, even during infective pulmonary exacerbation. One reason for this may be that excess airway secretions may prevent diffusion of gaseous NO into the airway lumen. We hypothesised that exhaled NO may not reflect total NO production in chronically suppurative airways and investigated nitrite as another marker of NO production. METHODS: Breath condensate nitrite concentration and exhaled NO levels were measured in 21 clinically stable patients with cystic fibrosis of mean age 26 years and mean FEV1 57% and 12 healthy normal volunteers of mean age 31 years. Breath condensate was collected with a validated method which excluded saliva and nasal air contamination and nitrite levels were measured using the Griess reaction. Exhaled NO was measured using a sensitive chemiluminescence analyser (LR2000) at an exhalation rate of 250 ml/s. Fourteen patients with cystic fibrosis had circulating plasma leucocyte levels and differential analysis performed on the day of breath collection. RESULTS: Nitrite levels were significantly higher in patients with cystic fibrosis than in normal subjects (median 1.93 microM compared with 0.33 microM). This correlated positively with circulating plasma leucocytes and neutrophils (r = 0.6). In contrast, exhaled NO values were not significantly different from the normal range (median 3.8 ppb vs 4.4 ppb). There was no correlation between breath condensate nitrite and lung function and between breath condensate nitrite and exhaled NO. CONCLUSIONS: Nitrite levels in breath condensate were raised in stable patients with cystic fibrosis in contrast to exhaled NO. This suggests that nitrite levels may be a more useful measure of NO production and possibly airways inflammation in suppurative airways and that exhaled NO may not reflect total NO production.

Nitrogen and Oxygen Regulation of Bacillus subtilis nasDEF Encoding NADH-Dependent Nitrite Reductase by TnrA and ResDE

Abstract: The nitrate and nitrite reductases of Bacillus subtilis have two different physiological functions. Under conditions of nitrogen limitation, these enzymes catalyze the reduction of nitrate via nitrite to ammonia for the anabolic incorporation of nitrogen into biomolecules. They also function catabolically in anaerobic respiration, which involves the use of nitrate and nitrite as terminal electron acceptors. Two distinct nitrate reductases, encoded by narGHI and nasBC, function in anabolic and catabolic nitrogen metabolism, respectively. However, as reported herein, a single NADH-dependent, soluble nitrite reductase encoded by the nasDE genes is required for both catabolic and anabolic processes. The nasDE genes, together with nasBC (encoding assimilatory nitrate reductase) and nasF (required for nitrite reductase siroheme cofactor formation), constitute the nas operon. Data presented show that transcription of nasDEF is driven not only by the previously characterized nas operon promoter but also from an internal promoter residing between the nasC and nasD genes. Transcription from both promoters is activated by nitrogen limitation during aerobic growth by the nitrogen regulator, TnrA. However, under conditions of oxygen limitation, nasDEF expression and nitrite reductase activity were significantly induced. Anaerobic induction of nasDEF required the ResDE two-component regulatory system and the presence of nitrite, indicating partial coregulation of NasDEF with the respiratory nitrate reductase NarGHI during nitrate respiration.

Helicobacter pylori is killed by nitrite under acidic conditions

Abstract: Background—Due to the expression of urease, Helicobacter pylori is able to establish itself in the human stomach under acidic conditions. A novel host defence mechanism was recently proposed, suggesting that the formation of salivary nitrite in symbiosis with facultative anaerobic bacteria in the oropharynx, is aimed at enhancing the antimicrobial activity of gastric juice. Aims—To investigate whether the addition of nitrite in physiological concentrations influences the resistance of H pylori to acid. Methods—H pylori cultured from fresh gastric biopsy specimens was exposed for 30 minutes to normal saline and to HCl/KCl buVer (0.2M) at pH 2 with urea (5 mM) added. The influence of potassium nitrite (50‐1000 µmol/l) on bacterial survival was determined. Results—Addition of nitrite (1 mM) to acidic solutions (pH 2) resulted in complete kill of H pylori within 30 minutes exposure time whereas acid alone allowed the organism to survive (p 500 µmol/l. Conclusion—Acidified nitrite has antibacterial activity against H pylori. This should prompt further research into the eVect of salivary nitrite on the survival of H pylori in the human stomach. (Gut 1998;42:334‐337)

Physiological and molecular biological characterization of ammonia oxidation of the heterotrophic nitrifier Pseudomonas putida.

Abstract: The heterotrophic nitrifier Pseudomonas putida aerobically oxidized ammonia to hydroxylamine, nitrite, and nitrate. Product formation was accompanied by a small but significant release of NO, whereas N2O evolution could not be detected under the assay conditions employed. The isolate reduced nitrate to nitrite and partially further to NO under anaerobic conditions. Aerobically grown cells utilized γ-aminobutyrate as a carbon source and as a N-source by ammonification. The physiological experiments, in particular the inhibition pattern by C2H2, indicated that P. putida expressed an ammonia monooxigenase. DNA-hybridization with an amoA gene probe coding for the smaller subunit of the ammonia monooxigenase of Nitrosomonas europaea allowed us to identify, to clone, and to sequence a region with an open reading frame showing distinct sequence similarities to the amoA gene of autotrophic ammonia oxidizers.

Microbial Nitrate-Dependent Oxidation of Ferrous Iron in Activated Sludge

Abstract: A biological reduction of nitrate and nitrite was found to take place in activated sludge concomitantly with the oxidation of ferrous iron to ferric iron. This process was shown to be predominantly biological and present in different types of activated sludge treatment plants with variable rates. The highest activity was found in plants with biological nitrogen and phosphorus removal. The highest Fe(II)-dependent nitrate removal rate was found to be 0.31 mmol NO3- (g VSS)-1 h-1, which corresponded to 68% of the maximum dissimilatory nitrate reduction rate in the presence of lactate. The Fe(II)-dependent nitrate removal rate was strongly pH-dependent with a maximal rate at pH 8 of almost four times the rate at pH 6. The main product of Fe(II)-dependent nitrate removal was most probably dinitrogen, as no accumulation of ammonia, nitrous oxide, or nitrite could be observed. The process may be of significance in the activated sludge treatment plant with regard to nitrate removal and with regard to the reoxida...

Ferrate(VI) oxidation of aqueous cyanide

Abstract: The rates of oxidation of cyanide with Fe(VI) were measured as a function of pH and temperature. The reaction was found to be first order for each reactant. The rates decrease with increasing pH. The energy of activation was found to be 38.9 {+-} 1.0 kJ mol{sup {minus}1} at pH 9.0. The removal of cyanide by oxidation with Fe(VI) was studied at pH 7.5, 9.0, and 12.0. Fe(VI) removal efficiency was greater at pH 9.0 than at pH 7.5 and 12.0. At pH 9.0, Fe(VI) molar consumption was nearly equal to that of oxidized cyanide. Cyanate and nitrite ions were identified as the products of the reaction at pH 7.5. The experiments indicated 1:1 stoichiometric conversion of cyanide to nitrite ion at pH 9.0 and 12.0. Experiments were conducted to test the Fe(VI) removal efficiency of cyanide in electroplating rinsewater. The results indicate that Fe(VI) has the potential to serve as a reliable and safe oxidative treatment for removing cyanide in wastewater effluent.

Catalytic liquid‐phase nitrite reduction: Kinetics and catalyst deactivation

Abstract: Liquid-phase reduction using a solid catalyst provides a potential technique for the removal of nitrites from waters. Activity and selectivity measurements were performed for a wide range of reactant concentrations and reaction conditions in an isothermal semi-batch slurry reactor, which was operated at temperatures below 298 K and atmospheric pressure. The effects of catalyst loading and initial nitrite concentration on the reaction rate were also investigated. The Pd monometallic catalysts were found to be advantageous over the Pd-Cu bimetallic catalyst with respect to either reaction activity or selectivity. Among the catalysts tested, minimum ammonia formation was observed for the Pd(1 wt.%)/{gamma}-Al{sub 2}O{sub 3} catalyst. The proposed intrinsic rate expression for nitrite disappearance over the most selective catalyst is based on the steady-state adsorption model of Hinshelwood, which accounts for a dissociative hydrogen adsorption step on the catalyst surface and an irreversible surface reaction step between adsorbed hydrogen species and nitrite ions in the Helmholtz layer. Both processes occur at comparable rates. An exponential decay in the activity of Pd(1 wt. %)/{gamma}-Al{sub 2}O{sub 3} catalyst has been observed during the liquid-phase nitrite reduction. This is attributed to the catalyst surface deprotonation, which occurs due to the partial neutralization of stoichiometrically produced more » hydroxide ions with carbon dioxide. « less