Showing papers on "Nitrite published in 2006"

Biological nitrogen removal with nitrification and denitrification via nitrite pathway

Abstract: Presently, the wastewater treatment practices can be significantly improved through the introduction of new microbial treatment technologies. To meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of ammonium from wastewater have to be implemented. Partial nitrification to nitrite was reported to be technically feasible and economically favorable, especially when wastewater with high ammonium concentrations or low C/N ratios is treated. For successful implementation of the technology, the critical point is how to maintain partial nitrification of ammonium to nitrite. Partial nitrification can be obtained by selectively inhibiting nitrite oxidizing bacteria through appropriate regulation of the system's DO concentration, microbial SRT, pH, temperature, substrate concentration and load, operational and aeration pattern, and inhibitor. The review addressed the microbiology, its consequences for their application, the current status regarding application, and the future developments.

Ceruloplasmin is a NO oxidase and nitrite synthase that determines endocrine NO homeostasis

Abstract: Nitrite represents a bioactive reservoir of nitric oxide (NO) that may modulate vasodilation, respiration and cytoprotection after ischemia-reperfusion injury. Although nitrite formation is thought to occur via reaction of NO with oxygen, this third-order reaction cannot compete kinetically with the reaction of NO with hemoglobin to form nitrate. Indeed, the formation of nitrite from NO in the blood is limited when plasma is substituted with physiological buffers, which suggests that plasma contains metal-based enzymatic pathways for nitrite synthesis. We therefore hypothesized that the multicopper oxidase, ceruloplasmin, could oxidize NO to NO+, with subsequent hydration to nitrite. Accordingly, plasma NO oxidase activity was decreased after ceruloplasmin immunodepletion, in ceruloplasmin knockout mice and in people with congenital aceruloplasminemia. Compared to controls, plasma nitrite concentrations were substantially reduced in ceruloplasmin knockout mice, which were more susceptible to liver infarction after ischemia and reperfusion. The extent of hepatocellular infarction normalized after nitrite repletion. These data suggest new functions for the multicopper oxidases in endocrine NO homeostasis and nitrite synthesis, and they support the hypothesis that physiological concentrations of nitrite contribute to hypoxic signaling and cytoprotection.

Nitrite as a vascular endocrine nitric oxide reservoir that contributes to hypoxic signaling, cytoprotection, and vasodilation

Abstract: Accumulating evidence suggests that the simple and ubiquitous anion salt, nitrite (NO(2)(-)), is a physiological signaling molecule with potential roles in intravascular endocrine nitric oxide (NO) transport, hypoxic vasodilation, signaling, and cytoprotection after ischemia-reperfusion. Human and animal studies of nitrite treatment and NO gas inhalation provide evidence that nitrite mediates many of the systemic therapeutic effects of NO gas inhalation, including peripheral vasodilation and prevention of ischemia-reperfusion-mediated tissue infarction. With regard to nitrite-dependent hypoxic signaling, biochemical and physiological studies suggest that hemoglobin possesses an allosterically regulated nitrite reductase activity that reduces nitrite to NO along the physiological oxygen gradient, potentially contributing to hypoxic vasodilation. An expanded consideration of nitrite as a hypoxia-dependent intrinsic signaling molecule has opened up a new field of research and therapeutic opportunities for diseases associated with regional hypoxia and vasoconstriction.

Anaerobic ammonium oxidation in the oxygen-deficient waters off northern Chile

Abstract: We investigated the pathways of N2 production in the oxygen-deficient water column of the eastern tropical South Pacific off Iquique, Chile, at 20uS, through short anoxic incubations with 15N-labelled nitrogen compounds. The location was characterized by steep chemical gradients, with oxygen decreasing to below detection at ,50-m depth, while nitrite reached 6 mmol L21 and ammonium was less than 50 nmol L21. Ammonium was oxidized to N2 with no lag phase during the incubations, and when only NH þ was 15N-labeled, 15N appeared in the form of 14N15N, whereas 15N15N was not detected. Likewise, nitrite was reduced to N2 at rates similar to the rates of ammonium oxidation, and when only NO 2 was 15N-labeled, 15N appeared mainly as 14 N 15 N, whereas 15 N 15 N appeared in only one incubation. These observations indicate that ammonium was oxidized and nitrite was reduced through the anammox reaction, whereas denitrification was generally not detected and, therefore, was a minor sink for nitrite. Anammox rates were highest, up to 0.7 nmol N2 L 21 h 21 , just below the oxycline, whereas rates were undetectable, ,0.2 nmol N2 L21 h21, deeper in the oxygen-deficient zone. Instead of complete denitrification to N2, oxidation of organic matter during the incubations may have been coupled to reduction of nitrate to nitrite. This process was evident from strong increases in nitrite concentrations toward the end of the incubations. The results point to anammox as an active process in the major open-ocean oxygen-deficient zones, which are generally recognized as important sites of denitrification. Still, denitrification remains the simplest explanation for most of the nitrogen deficiency in these zones.

Unraveling the Reactions of Nitric Oxide, Nitrite, and Hemoglobin in Physiology and Therapeutics

Abstract: The ability of oxyhemoglobin to inhibit nitric oxide (NO)-dependent activation of soluble guanylate cyclase and vasodilation provided some of the earliest experimental evidence that NO was the endothelium-derived relaxing factor (EDRF). The chemical behavior of this dioxygenation reaction, producing nearly diffusion limited and irreversible NO scavenging, presents a major paradox in vascular biology: The proximity of large amounts of oxyhemoglobin (10 mmol/L) to the endothelium should severely limit paracrine NO diffusion from endothelium to smooth muscle. However, several physical factors are now known to mitigate NO scavenging by red blood cell encapsulated hemoglobin. These include diffusional boundaries around the erythrocyte and a red blood cell free zone along the endothelium in laminar flowing blood, which reduce reaction rates between NO and red cell hemoglobin by 100- to 600-fold. Beyond these mechanisms that reduce NO scavenging by hemoglobin within the red cell, 2 additional mechanisms have been proposed suggesting that NO can be stored in the red blood cell either as nitrite or as an S-nitrosothiol (S-nitroso-hemoglobin). The latter controversial hypothesis contends that NO is stabilized, transported, and delivered by intra-molecular NO group transfers between the heme iron and beta-93 cysteine to form S-nitroso-hemoglobin (SNO-Hb), followed by hypoxia-dependent delivery of the S-nitrosothiol in a process that links regional oxygen deficits with S-nitrosothiol-mediated vasodilation. Although this model has generated a field of research examining the potential endocrine properties of intravascular NO molecules, including S-nitrosothiols, nitrite, and nitrated lipids, a number of mechanistic elements of the theory have been challenged. Recent data from several groups suggest that the nitrite anion (NO2-) may represent the major intravascular NO storage molecule whose transduction to NO is made possible through an allosterically controlled nitrite reductase reaction with the heme moiety of hemoglobin. As subsequently understood, the hypoxic generation of NO from nitrite is likely to prove important in many aspects of physiology, pathophysiology, and therapeutics.

Carcinogenicity of nitrate, nitrite, and cyanobacterial peptide toxins

Abstract: In June, 2006, 19 scientists from eight countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to assess the carcinogenicity of ingested nitrate and nitrite, and the cyanobacterial peptide toxins microcystin-LR and nodularins. These agents are linked environmentally through the runoff of agricultural fertilisers that increase nitrogen concentrations in surface water and groundwater, and that could contribute to cyanobacterial growth in surface water. The assessments will be published as volume 94 of the IARC Monographs. Nitrate and nitrite are naturallyoccurring ions. In the past century, the global nitrogen cycle has been increasingly aff ected by nitrogen fi xation for agricultural activities, which now exceeds the amount that occurs naturally. Both groundwater and surface water can be contaminated by excess nitrate as a result of agricultural activities. Human exposure to nitrate and nitrite is mainly from the ingestion of food. Important sources include vegetables, cereal products, and cured meat. Drinking-water is generally not the main source of nitrate, unless concentrations exceed the WHO guideline of 50 mg/L, which is especially found in contaminated groundwater. Ingested nitrate (NO3) is excreted in the saliva and reduced to nitrite (NO 2) mainly by oral bacteria. Under acidic conditions in the stomach, nitrite then reacts readily with nitrosatable compounds, especially sec ondary amines and alkyl amides, to generate N-nitroso compounds. Several N-nitroso compounds are potential human carcinogens. The nitrosation reactions can be inhibited by the presence of vitamin C or other antioxidants. Some epidemiological studies assessed the risk of cancer in people who had high intake of nitrite or nitrate and low intake of vitamin C, a dietary pattern that could result in increased endogenous formation of N-nitroso compounds. The Working Group weighted these studies more heavily than studies without this information. From the epidemiological studies of nitrate in food, no increased risk of cancer was seen. For nitrate in drinkingwater, epidemiological studies were few, exposure levels were low, and endogenous nitrosation was not often considered. For ingested nitrite, the risk for stomach cancer was investigated in seven well-designed case-control studies. Six of these showed consistent, positive associations, four of which were signifi cant. Two studies looked at eff ect modifi cation, and the risk was most pronounced in people who had high nitrite and low vitamin C intake. Neither of the two cohort studies reported a clear positive association. No study accounted for potential confounding or eff ect modifi cation by Helicobacter pylori, an important risk factor for stomach cancer. For oesophageal cancer, two well-designed case-control studies investigated an association with nitrite intake. Both reported a positive association for nitrite intake overall; for people with high nitrite and low vitamin C intake, these associations were signifi cant. For brain tumours, two of fi ve casecontrol studies in children showed positive associations with nitrite intake. In one study, children born to mothers with the highest intake of nitrite from cured meat during pregnancy had a three-fold increased risk for brain tumours. The other study reported an increased risk for astroglial brain tumours in the children of mothers whose drinking-water had high nitrite concentrations. For adult brain cancer, no clear pattern emerged from seven case-control studies. The Working Group concluded that there is “limited evidence of carcinogenicity” for nitrite in food based on the association with stomach cancer. For nitrate in food and nitrate or nitrite in drinking-water, the studies provide “inadequate evidence of carcinogenicity”. No increased incidence of tumours was recorded in mice and rats if nitrate alone was added to the drinking-water or to the diet, providing inadequate evidence of carcinogenicity. Mice given nitrite in drinking-water showed a signifi cant trend in the incidence of forestomach papillomas and carcinomas combined. Rats exposed to nitrite in utero and throughout life had an increased incidence of lymphoreticular tumours, and mice with similar exposure had raised incidences of lymphoma and lung tumours. These results provide limited evidence of carcinogenicity for nitrite alone. Many studies of mice and rats tested nitrite in combination with specifi c secondary or tertiary amines or amides, added to the diet or drinkingwater, or by gastric intubation. Most combinations resulted in increased incidences of benign and malignant tumours at many organ sites. The Working Group concluded that these results provided “suffi cient evidence of carcinogenicity” for nitrite in combination with amines or amides. The combination of positive and negative results from epidemiological Upcoming meetings

Early Intravenous Infusion of Sodium Nitrite Protects Brain Against In Vivo Ischemia-Reperfusion Injury

Abstract: Background and Purpose— The rate of nitric oxide (NO) generation from nitrite is linearly dependent on reductions in oxygen and pH levels. Recently, nitrite-derived NO has been reported to exert a profound protection against liver and heart ischemia-reperfusion injury. In this study, we hypothesized that nitrite would be reduced to NO in the ischemic brain and exert NO-dependent neuroprotective effects. Methods— Cerebral ischemia-reperfusion injury was induced by intraluminal thread occlusion of middle cerebral artery in the adult male rats. Solutions of sodium nitrite were infused intravenously at the time of reperfusion. Sodium nitrate and carboxy-PTIO (30 minutes before ischemic surgery), a direct NO scavenger, were infused for comparisons. Results— Nitrite reduced infarction volume and enhanced local cerebral blood flow and functional recovery. The effects were observed at concentrations of 48 nmol and 480 nmol, but not at 4800 nmol nitrite and 480 nmol nitrate. The neuroprotective effects of nitrite ...

Formation and possible roles of nitric oxide in plant roots

Abstract: Nitric oxide has been reported to act as a signalling molecule in different plant tissues and to participate in a variety of physiological processes. It is produced by different enzymes and sources. The root-specific plasma membrane-bound enzymes forming NO from the substrates nitrate and nitrite are of particular interest because roots serve as interfaces between plants and the soil. The co-ordinated activity of the root-specific plasma membrane-bound nitrate reductase (PM-NR) and nitrite:NO reductase (NI-NOR) suggests that NO might also be involved in root signalling and development. The rate of enzymatic production of this NO depends largely on the environmental conditions, mainly the availability of nitrate and oxygen and it is proposed that this NO plays a role during anoxia as an indicator of the external nitrate availability and in regulating symbiotic interactions at the root surface.

An S-nitrosothiol (SNO) synthase function of hemoglobin that utilizes nitrite as a substrate.

Abstract: Red blood cells (RBCs) act as O2-responsive transducers of vasodilator and vasoconstrictor activity in lungs and tissues by regulating the availability of nitric oxide (NO). Vasodilation by RBCs is impaired in diseases characterized by hypoxemia. We have proposed that the extent to which RBCs constrict vs. dilate vessels is, at least partly, controlled by a partitioning between NO bound to heme iron and to Cysβ93 thiol of hemoglobin (Hb). Hemes sequester NO, whereas thiols deploy NO bioactivity. In recent work, we have suggested that specific micropopulations of NO-liganded Hb could support the chemistry of S-nitrosohemoglobin (SNO-Hb) formation. Here, by using nitrite as the source of NO, we demonstrate that a (T state) micropopulation of a heme-NO species, with spectral and chemical properties of Fe(III)NO, acts as a precursor to SNO-Hb formation, accompanying the allosteric transition of Hb to the R state. We also show that at physiological concentrations of nitrite and deoxyHb, a S-nitrosothiol precursor is formed within seconds and produces SNO-Hb in high yield upon its prompt exposure to O2 or CO. Deoxygenation/reoxygenation cycling of oxyHb in the presence of physiological amounts of nitrite also efficiently produces SNO-Hb. In contrast, high amounts of nitrite or delays in reoxygenation inhibit the production of SNO-Hb. Collectively, our data provide evidence for a physiological S-nitrosothiol synthase activity of tetrameric Hb that depends on NO-Hb micropopulations and suggest that dysfunction of this activity may contribute to the pathophysiology of cardiopulmonary and blood disorders.

Nitrite concentration influences the population structure of Nitrospira‐like bacteria

Abstract: Summary Chemolithoautotrophic nitrite oxidizers of the genus Nitrospira are a monophyletic but diverse group of organisms, are widely distributed in many natural habitats, and play a key role in nitrogen elimination during biological wastewater treatment. Phylogenetic analyses of cloned 16S rRNA genes and fluorescence in situ hybridization with newly developed rRNA-tar- geted oligonucleotide probes revealed coexistence of uncultured members of sublineages I and II of the genus Nitrospira in biofilm and activated sludge samples taken from nitrifying wastewater treatment plants. Quantitative microscopic analyses of their spatial arrangement relative to ammonia oxidizers in the biofilm and activated sludge flocs showed that members of the Nitrospira sublineage I occurred sig- nificantly more often in immediate vicinity to ammo- nia oxidizers than would be expected from random community assembly while such a relationship was not observed for Nitrospira sublineage II. This spatial distribution suggested a niche differentiation of these coexisting Nitrospira populations with respect to their preferred concentrations of nitrite. This hypothesis was tested by mathematical modelling of nitrite con- sumption and resulting nitrite gradients in nitrifying biofilms and by quantifying the abundance of sublin- eage I and II Nitrospira in activated sludge during incubations with nitrite in different concentrations. Consistent with the observed localization patterns, a higher nitrite concentration selected for sublineage I but suppressed sublineage II Nitrospira .

Sodium nitroprusside, cyanide, nitrite, and nitrate break Arabidopsis seed dormancy in a nitric oxide-dependent manner.

Abstract: The seeds of many plant species are dormant at maturity and dormancy loss is a prerequisite for germination. Numerous environmental and chemical treatments are known to lessen or remove seed dormancy, but the biochemical changes that occur during this change of state are poorly understood. Several lines of research have implicated nitric oxide (NO) as a participant in this process. Here, we show that dormant seeds of Arabidopsis thaliana (L.) Heynh. will germinate following treatment with the NO donor sodium nitroprusside (SNP), cyanide (CN), nitrite or nitrate. In all cases, the NO scavenger c-PTIO effectively promotes the maintenance of seed dormancy. c-PTIO does not, however, inhibit germination of fully after-ripened seeds, and c-PTIO does not interact directly with nitrite, nitrate or CN. We also show that volatile CN effectively breaks dormancy of Arabidopsis seeds, and that CN is the volatile compound in SNP that promotes dormancy loss. Our data support the hypothesis that NO is a signaling molecule that plays an important role in the loss of seed dormancy.

The inhibitory effects of free nitrous acid on the energy generation and growth processes of an enriched nitrobacter culture.

Abstract: The inhibitory effects of nitrite (NO2-)/free nitrous acid (HNO2−FNA) on the metabolism of Nitrobacter were investigated using a method allowing the decoupling of the growth and energy generation processes. A lab-scale sequencing batch reactor was operated for the enrichment of a Nitrobacter culture. Fluorescent in situ hybridization (FISH) analysis showed that 73% of the bacterial population was Nitrobacter. Batch tests were carried out to assess the oxygen and nitrite consumption rates of the enriched culture at low and high nitrite levels, in the presence or absence of inorganic carbon. It was observed that in the absence of CO2, the Nitrobacter culture was able to oxidize nitrite at a rate that is 76% of that in the presence of CO2, with an oxygen consumption rate that is 85% of that measured in the presence of CO2. This enabled the impacts of nitrite/FNA on the catabolic and anabolic processes of Nitrobacter to be assessed separately. FNA rather than nitrite was likely the actual inhibitor to the Nit...

Competition between nitrospira spp. and nitrobacter spp. in nitrite-oxidizing bioreactors

Abstract: In this work the question was addressed if in nitrite-oxidizing activated sludge systems the environmental competition between Nitrobacter spp. and Nitrospira spp., which only recently has been discovered to play a role in these systems, is affected by the nitrite concentrations. Two parallel chemostats were inoculated with nitrifying-activated sludge containing Nitrospira and operated under identical conditions. After addition of Nitrobacter to both chemostats, the nitrite concentration in the influent of one of the chemostats was increased such that nitrite peaks in the bulk liquid of this reactor were detected. The other chemostat served as control reactor, which always had a constant nitrite influent concentration. The relative cellular area (RCA) of Nitrospira and Nitrobacter was determined by quantitative fluorescence in situ hybridization (FISH). The nitrite perturbation stimulated the growth of Nitrobacter while in the undisturbed control chemostat Nitrospira dominated. Overall, the results of this experimental study support the hypothesis that Nitrobacter is a superior competitor when resources are abundant, while Nitrospira thrive under conditions of resource scarcity. Interestingly, the dominance of Nitrobacter over Nitrospira, caused by the elevated nitrite concentrations, could not be reverted by lowering the available nitrite concentration to the original level. One possible explanation for this result is that when Nitrobacter is present at a certain cell density it is able to inhibit the growth of Nitrospira. An alternative explanation would be that the length of the experimental period was not long enough to observe an increase of the Nitrospira population.

Energetic Consequences of Nitrite Stress in Desulfovibrio vulgaris Hildenborough, Inferred from Global Transcriptional Analysis

Abstract: Many of the proteins that are candidates for bioenergetic pathways involved with sulfate respiration in Desulfovibrio spp. have been studied, but complete pathways and overall cell physiology remain to be resolved for many environmentally relevant conditions. In order to understand the metabolism of these microorganisms under adverse environmental conditions for improved bioremediation efforts, Desulfovibrio vulgaris Hildenborough was used as a model organism to study stress response to nitrite, an important intermediate in the nitrogen cycle. Previous physiological studies demonstrated that growth was inhibited by nitrite and that nitrite reduction was observed to be the primary mechanism of detoxification. Global transcriptional profiling with whole-genome microarrays revealed coordinated cascades of responses to nitrite in pathways of energy metabolism, nitrogen metabolism, oxidative stress response, and iron homeostasis. In agreement with previous observations, nitrite-stressed cells showed a decrease in the expression of genes encoding sulfate reduction functions in addition to respiratory oxidative phosphorylation and ATP synthase activity. Consequently, the stressed cells had decreased expression of the genes encoding ATP-dependent amino acid transporters and proteins involved in translation. Other genes up-regulated in response to nitrite include the genes in the Fur regulon, which is suggested to be involved in iron homeostasis, and genes in the Per regulon, which is predicted to be responsible for oxidative stress response.