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PubMed2001

Single stage biological nitrogen removal by nitritation and anaerobic ammonium oxidation in biofilm systems.

In full scale wastewater treatment plants with at times considerable deficits in the nitrogen balances, it could hitherto not be sufficiently explained which reactions are the cause of the nitrogen losses and which micro-organisms participate in the process. The single stage conversion of ammonium into gaseous end-products--which is henceforth referred to as deammonification--occurs particularly frequently in biofilm systems. In the meantime, one has succeeded to establish the deammonification processes in a continuous flow moving-bed pilot plant. In batch tests with the biofilm covered carriers, it was possible for the first time to examine the nitrogen conversion at the intact biofilm. Depending on the dissolved oxygen (DO) concentration, two autotrophic nitrogen converting reactions in the biofilm could be proven: one nitritation process under aerobic conditions and one anaerobic ammonium oxidation. With the anaerobic ammonium oxidation, ammonium as electron donor was converted with nitrite as electron acceptor. The end-product of this reaction was N2. Ammonium and nitrite did react in a stoichiometrical ratio of 1:1.37, a ratio which has in the very same dimension been described for the ANAMMOX-process (1:1.31 +/- 0.06). Via the oxygen concentration in the surrounding medium, it was possible to control the ratio of nitritation and anaerobic ammonium oxidation in the nitrogen conversion of the biofilm. Both processes were evenly balanced at a DO concentration of 0.7 mg/l, so that it was possible to achieve a direct, almost complete elimination of ammonium without addition of nitrite. One part of the provided ammonium did participate in the nitritation, the other in the anaerobic ammonium oxidation. Through the aerobic ammonium oxidation into nitrite within the outer oxygen supplied layers of the biofilm, the reaction partner was produced for the anaerobic ammonium oxidation within the inner layers of the biofilm.

Bacteria, Anaerobic↗

PubMed2004

Community analysis of ammonia oxidizer in the oxygen-limited nitritation stage of OLAND system by DGGE of PCR amplified 16S rDNA fragments and FISH.

OLAND (oxygen limited autotrophic nitrification and denitrification) nitrogen removal system was constructed by coupling with oxygen limited nitritation stage and anaerobic ammonium oxidation stage. Ammonia oxidizer, as a kind of key bacteria in N cycle, plays an important role at the oxygen limited nitritation stage of OLAND nitrogen removal system. In this study, specific amplification of 16S rDNA fragment of ammonia oxidizer by nested PCR, separation of mixed PCR samples by denaturing gradient gel electrophoresis (DGGE), and the quantification of ammonia oxidizer by fluorescence in situ hybridization (FISH) were combined to investigate the shifts of community composition and quantity of ammonia oxidizer of the oxygen limited nitritation stage in OLAND system. It showed that the community composition of ammonia oxidizer changed drastically when dissolved oxygen was decreased gradually, and the dominant ammonia oxidizer of the steady nitrite accumulation stage were completely different from that of the early stage of oxygen limited nitritation identified by DGGE. It was concluded that the Nitrosomonas may be the dominant genus of ammonia oxidizer at the oxygen limited nitritation stage of OLAND system characterized by nested PCR-DGGE and FISH, and the percentage of Nitrosomonas was 72.5% +/- 0.8% of ammonia oxidizer at the steady nitrite accumulation stage detected by FISH.

Ammonia↗

PubMed1982

Nitrite-induced volatile fecal mutagens: some preliminary studies.

Further studies are reported on the formation of volatile mutagens from normal human feces incubated with sodium nitrite at 37 degrees C. Volatile mutagens were detected using Ames' Salmonella typhimurium tester strain TA1535 on petrie plates inverted over samples in sealed containers. An optimal exposure period was shown to be approximately 24 hours. When plates inverted over samples were replaced periodically, mutagenicity during serial 24 hour or 48 hour periods could be measured. Mutagenicity was optimal during the second 24 hour period and the first 48 hour period with 0.6 M sodium nitrite, and in the first 24- and 48-hour period with 0.2 M sodium nitrite. Subsequent exposure periods showed decreasing mutagenicity with time. Because of the great differences in reactivity with nitrite in stools of healthy volunteers, the effect of mixing "high reacting" samples with "low reacting" samples were investigated. When "low reacting" samples were mixed with "high reacting" samples, a lower mutagenicity of the mixture was observed compared to a predicted "average" value. Autoclaving stool samples made very little difference in nitrite-induced mutagenicity and behavior in mixing experiments. Thus, fecal mutagens arise as a spontaneous chemical process involving nitrite ions and both dietary and flora factors may be important in their production or absence.

Adult↗

PubMed1989

Mutagenicity of some alkyl nitrites used as recreational drugs.

When the AIDS epidemic was in its earliest stages, and prior to identification of HIV as the etiological factor, the use of volatile nitrites by the male homosexual community to enhance sexual activities appeared to have a significant role in this disease. Preliminary observations indicated that the portion of the male homosexual community which developed Kaposi's sarcoma were also heavy nitrite users. These nitrites had been demonstrated to be mutagenic in bacteria and thus it was postulated that they could be responsible for the appearance of the sarcoma. To evaluate further the genotoxic activity of these chemicals, six nitrites, including those most commonly used by homosexuals for sexual gratification, were selected for testing in the mouse lymphoma TK+/- and Salmonella typhimurium mutagenicity assays. One chemical, n-amyl nitrite, was negative in the mouse lymphoma assay, while the other five chemicals, n-butyl, isobutyl, iso-amyl, sec-butyl, and n-propyl nitrite, were positive. All six compounds were positive in the Salmonella assay. The mutagenic and known toxic effects of these chemicals remain a concern because a large population of teenagers and young adults continue to abuse these substances.

Amyl Nitrite↗

PubMed1990

Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria.

Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate- and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5'-TACCAT-3' and 5'-CTCCTT-3', were found in the promoters of operons known to be activated or repressed by the NarL protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗

PubMed1989

Oxidation of cardiac myoglobin in vivo by sodium nitrite or hydroxylamine.

A non-vascularized fish heart model was used to assess the oxidation of cardiac myoglobin in vivo by compounds known to cause methemoglobinemia. Buffalo sculpin (Enophrys bison) were cannulated from the afferent branchial artery to permit repeated blood sampling and injected intraperitoneally with sodium nitrite, hydroxylamine or aniline. Methemoglobin was formed by sublethal levels of sodium nitrite or hydroxylamine. For hydroxylamine, the time to peak effect was less than 1 h. For sodium nitrite, the onset was less rapid and the effect more prolonged. Aniline had no effect on hemoglobin at any concentration tested. Cardiac myoglobin, assayed at the time of peak effect on hemoglobin, was oxidized in a dose-dependent manner by sodium nitrite or hydroxylamine. At high doses of sodium nitrite (50 and 100 mg/kg), the oxidation of myoglobin exceeded that of hemoglobin. The reverse was true of hydroxylamine at all concentrations tested. This study suggests that possibility that cardiac myoglobin is oxidized in occupational or other exposures to sodium nitrite, hydroxylamine and related compounds.

Animals↗

PubMed1994

Regulation of nitrate and nitrite reductase synthesis in enterobacteria.

Enterobacteria use nitrate and nitrite both as electron acceptors and as sources of nitrogen for biosynthesis. Nitrate is reduced through nitrite to ammonium in both cases. The enzymes and structural genes for nitrate/nitrite respiration and assimilation are distinct, and are subject to different patterns of regulation. Respiratory enzyme synthesis is indifferent to the availability of ammonium, and is induced by anaerobiosis via the FNR protein. Respiratory enzyme synthesis is further induced by nitrate or nitrite via the NARL and NARP proteins, which are response regulators of two-component regulatory systems. The cognate sensor proteins NARX and NARQ monitor the availability of nitrate and nitrite, and control the activity of the NARL and NARP DNA-binding proteins accordingly. Additionally, nitrate represses the synthesis of respiratory nitrite reductase, and this control is mediated by the NARL protein. Assimilatory enzyme synthesis is indifferent to the availability of oxygen, and is induced by ammonium limitation via the NTRC protein. Assimilatory enzyme synthesis is further induced by nitrate or nitrite via the NASR protein, which may act as a transcription antiterminator. Even though the respiratory and assimilatory enzyme systems are genetically distinct and subject to different forms of regulation, the structural and regulatory genes are closely linked on the Klebsiella pneumoniae chromosome.

Anaerobiosis↗

PubMed1982

Combined treatment of preimplantation mouse embryos in vitro with sodium nitrite and x-rays.

Man takes up nitrite in a considerable amount. Effects of nitrite on DNA have been reported; therefore, interaction between nitrite and radiation might be possible. Preimplantation mouse embryos in vitro were treated with a combination of sodium nitrite (1 mM or 2.5 mM) and X-rays (0.94 Gy) in order to obtain some information whether radiation risk is influenced by the presence of nitrite. The microscopic visible development up to 144 h post conceptionem (h p.c.), the number of cell nuclei, and the number of micronuclei were determined. None of the experimental results gives any indication that radiation risk is influenced by nitrite. All effects after combined treatment correspond to the sum of the single effects.

Animals↗

PubMed1985

Volatile nitrites. Use and adverse effects related to the current epidemic of the acquired immune deficiency syndrome.

Early reports of the acquired immune deficiency syndrome (AIDS) in homosexual men suggested that the cause might be related to homosexual life-style practices, including use of recreational drugs. Inhalation of volatile nitrites is a possible contributing factor in AIDS because their pharmacologic properties lead to toxicity. Metabolism of N-nitroso compounds produces mutagens, teratogens, and potent carcinogens in 39 different animal species, and volatile nitrites have deleterious effects on human lymphocytes in vitro and in vivo. In relation to the current AIDS epidemic, the timing of production and sales of volatile nitrites for recreational use is the only new life-style factor that might answer the question "why AIDS now?" Prevalence of nitrite use among male homosexuals is very high, and almost every reported case of Kaposi's sarcoma during the past three years includes a history of prior nitrite use. The age of the group of patients in whom Kaposi's sarcoma and AIDS are developing is consistent with a cohort initially exposed seven to 10 years ago. Cessation of nitrite use could reduce the epidemic.

Acquired Immunodeficiency Syndrome↗

PubMed1988

Antigenic similarities between ferredoxin-dependent nitrite reductase and glutamate synthase from Chlamydomonas reinhardtii.

Polyclonal antisera were prepared against ferredoxin-nitrite reductase (EC 1.7.7.1) and ferredoxin-glutamate synthase (glutamate synthase (ferredoxin); EC 1.4.7.1) from the green alga Chlamydomonas reinhardtii. The anti-glutamate synthase antibodies recognized both glutamate synthase and nitrite reductase, but inhibited only the ferredoxin-linked activity of the latter enzyme and not the activity dependent on methyl viologen. Analogously, the anti-nitrite reductase antibodies recognized glutamate synthase and nitrite reductase but the first enzyme was only poorly inhibited. Free ferredoxin protected the nitrite reductase against its inactivation by anti-glutamate synthase antibodies. These results indicate that the ferredoxin-dependent glutamate synthase and nitrite reductase from this alga share common antigenic determinants, and that these are located at the ferredoxin-binding domains.

Chlamydomonas↗

PubMed1988

Sister chromatid exchanges and micronuclei formations induced by sorbic acid and sorbic acid-nitrite in vivo in mice.

The in vivo induction of sister chromatid exchanges and micronuclei formations by acute treatment with different concentrations of sorbic acid and by nitrite, individually and in combination, was studied in bone marrow cells of mice. A significant increase in the frequency of sister chromatid exchanges was only observed with the three higher concentrations of sorbic acid when compared to a distilled water control. Sodium nitrite produced a significant increase at all doses tested. A combination of half the concentration of sorbic acid and of sodium nitrite gave an additive effect over that of sorbic acid or sodium nitrite alone. In the micronucleus assay, the highest dose of sorbic acid (150 mg/kg body weight) produced a significant increase in micronuclei formations compared to the distilled water control. Sodium nitrite alone induced significant numbers of micronuclei at all concentrations tested when compared to the negative control. However, a combination of half the concentration of sorbic acid and of sodium nitrite gave synergistic effects which could possibly be ascribed to the formation of certain genotoxic compounds in vivo.

Animals↗

PubMed1985

Autocatalytic oxidation of hemoglobin induced by nitrite: activation and chemical inhibition.

The nitrite ion is a direct causative agent for methemoglobinemia. Oxidation of hemoglobin to methemoglobin under aerobic conditions is induced by nitrite, catalyzed by methemoglobin in the presence of hydrogen peroxide, and inhibited by chemical reagents ranging from cysteine and ascorbic acid to sulfite. The stoichiometry of nitrate production is dependent on the initial [NO2-]/[HbO2] ratio, but reaches a limiting value of 1:1 [NO3-]: [Hb+] when [NO2-]/[HbO2] greater than 8. Ascorbic acid is an exceptionally effective inhibitor for the autocatalytic oxidation, but its use does not affect the stoichiometry of nitrate formation. Sulfite reduces nitrate production to a level that is half that observed in its absence. These chemical inhibitors act upon the rapid autocatalytic stage for hemoglobin oxidation, but they do not influence the slow direct oxidation of hemoglobin by nitrite. The autocatalytic stage for hemoglobin oxidation results from nitrogen dioxide formed from nitrite through the peroxidase activity of methemoglobin. Peroxide and methemoglobin are formed during the initiation stage by electron transfer from nitrite that is kinetically first order in oxyhemoglobin and in nitrite.

Ascorbic Acid↗

PubMed2006

Evidence for nitrite reductase activity in intact mouse Leydig tumor cells.

Nitric oxide (NO) supposedly derived via L-arginine-NO synthase (NOS) pathway has been implicated in inhibiting steroidogenesis by binding the heme moiety of steroidogenic enzymes. Previously, nitrite, and to a lesser extent nitrate ions inhibited steroidogenesis via NO by hitherto unknown reduction mechanism. Recently, a putative mammalian nitrite reductase activity ascribed to complex III of mitochondrial respiratory chain complexes (MRCC) has been reported, where MRCC inhibitors reduced NO production from nitrite variably. We thus studied the effects of MRCC inhibitors on testosterone production in mouse Leydig tumor cells (MLTC-1) without (basal) or with human chorionic gonadotropin (hCG) stimulation. In stimulated MLTC-1, MRCC inhibitors decreased testosterone production, order being: complex III (antimycin A and myxothiazol) > complex I (rotenone) > complex II (thenoyltrifluoroacetone), while cAMP production increased inversely. In unstimulated MLTC-1, MRCC inhibitors in same order, increased basal testosterone production, which correlated inversely with the percentage inhibition of NO production, with one exception; while antimycin A did not inhibit NO production in the nitrite reductase study mentioned above, it increased basal testosterone production in the present study. While MLTC-1 expressed mRNA for endothelial and neuronal, but not inducible NOS, various stimulators and inhibitors of L-arginine-NOS pathway had no effect on basal testosterone production in MLTC-1 or fresh Balb/c Leydig cells. Moreover, hCG increased nitrate uptake into MLTC-1, which suggests the gonadotropin aids nitrite and nitrate ions in their steroidogenesis inhibitory activity. In conclusion, this study supports the existence of a surrogate mammalian nitrite reductase and the dormancy of L-arginine-NOS pathway in MLTC-1.

Animals↗

PubMed1987

Nonautocatalytic methemoglobin formation by sodium nitrite under aerobic and anaerobic conditions.

Aerobic exposure of human hemoglobin in 1:1 molar ratio to sodium nitrite induced an immediate and progressive formation of methemoglobin. Neither lag nor autocatalytic phases were observed, contrary to what was seen when diluted hemoglobin in buffered solutions was used. Hemolyzed whole blood, washed red cells with their plasma replaced by saline, and whole blood were exposed to identical sodium nitrite concentrations. In the presence of oxygen, the speed of methemoglobin formation was three to four times faster in the hemolyzed and plasma-free samples than in whole blood. The maximum rate was reached within the first minute of the reaction. Restoring plasma to washed red cells reduced the rate to that of whole blood; restoring plasma to hemolyzed red cells had no effect on rate. We advance the hypothesis that sodium nitrite or its derivatives form a complex with some element of the blood plasma which slows the passage of nitrite through the red cell membrane without hindering the oxidative capacity of the nitrite. With no free oxygen present, whole blood, washed red cells in saline, and hemolyzed blood all showed a similar rate of methemoglobin formation when exposed to a 1:1 molar ratio of sodium nitrite. The presence of nitrosylhemoglobin formed in the anaerobic reaction seems to be a for the lack of changes seen in the reaction.

Carbon Dioxide↗

PubMed2002

Optical biosensor based on nitrite reductase immobilised in controlled pore glass.

The increasing concentration of nitrite in groundwater, rivers and lakes brings serious risks to the public health and to the environment. The aim of this work was the development of an optical biosensor for quantifying nitrite based on the activity of cytochrome cd(1) nitrite reductase immobilised in controlled pore glass (CPG) beads. The developed biosensor operates by measuring the optical reflectance of nitrite reductase, which shows spectroscopic changes when nitrite reversibly binds to the reduced form and oxidizes the enzyme. The optimisation of the immobilisation procedure showed that the immobilisation efficiency is highly dependent on the pH, being very low at basic pH, and that the maximum capacity of the CPG for the immobilisation of cd(1) was estimated in 57+/-10 mg cd(1)/g CPG. The CPG/cd(1) specific activity remained stable at 4 degrees C, decreasing only 10% in 15 days. No observed effects of the immobilisation on the enzyme characteristics were detected, regarding both the red/ox absorbance spectra and the enzyme specific activity, since the red/ox spectra are in good agreement with similar ones obtained for cd(1) in solution, and the specific activity at time zero (0.6 micromoles of NO(2)(-) reduced min(-1) mg of protein(-1)) is similar to that found for the soluble enzyme. The biosensor shows a sensitive response to increasing concentrations of nitrite in solution, especially at 460 nm, at which it showed higher sensitivity. The corresponding detection limit of 0.93 microM is well below the maximum admissible concentration imposed by European Community norms, of 2.2 microM.

Biosensing Techniques↗

PubMed1996

The genes YNI1 and YNR1, encoding nitrite reductase and nitrate reductase respectively in the yeast Hansenula polymorpha, are clustered and co-ordinately regulated.

The nitrite reductase-encoding gene (YNI1) from the yeast Hansenula polymorpha was isolated from a lambda EMBL3 H. polymorpha genomic DNA library, using as a probe a 481 bp DNA fragment from the gene of Aspergillus nidulans encoding nitrite reductase (niiA). An open reading frame of 3132 bp, encoding a putative protein of 1044 amino acids with high similarity with nitrite reductases from fungi, was located by DNA sequencing in the phages lambdaNB5 and lambdaJA13. Genes YNI1 and YNR1 (encoding nitrate reductase) are clustered, separated by 1700 bp. Northern blot analysis showed that expression of YNI1 and YNR1 is co-ordinately regulated; induced by nitrate and nitrite and repressed by sources of reduced nitrogen, even in the presence of nitrate. A mutant lacking nitrite reductase activity was obtained by deletion of the chromosomal copy of YNI1. The mutant does not grow in nitrate or in nitrite; it exhibits a similar level of transcription of YNR1 to the wild type, but the nitrate reductase enzymic activity is only about 50% of the wild type. In the presence of nitrate the delta ynil::URA3 mutant extrudes approx. 24 nmol of nitrite/h per mg of yeast (wet weight), about five times more than the wild type.

Amino Acid Sequence↗

PubMed2003

Nitrite reductase activity of sulphate-reducing bacteria prevents their inhibition by nitrate-reducing, sulphide-oxidizing bacteria.

Sulphate-reducing bacteria (SRB) can be inhibited by nitrate-reducing, sulphide-oxidizing bacteria (NR-SOB), despite the fact that these two groups are interdependent in many anaerobic environments. Practical applications of this inhibition include the reduction of sulphide concentrations in oil fields by nitrate injection. The NR-SOB Thiomicrospira sp. strain CVO was found to oxidize up to 15 mM sulphide, considerably more than three other NR-SOB strains that were tested. Sulphide oxidation increased the environmental redox potential (Eh) from -400 to +100 mV and gave 0.6 nitrite per nitrate reduced. Within the genus Desulfovibrio, strains Lac3 and Lac6 were inhibited by strain CVO and nitrate for the duration of the experiment, whereas inhibition of strains Lac15 and D. vulgaris Hildenborough was transient. The latter had very high nitrite reductase (Nrf) activity. Southern blotting with D. vulgaris nrf genes as a probe indicated the absence of homologous nrf genes from strains Lac3 and Lac6 and their presence in strain Lac15. With respect to SRB from other genera, inhibition of the known nitrite reducer Desulfobulbus propionicus by strain CVO and nitrate was transient, whereas inhibition of Desulfobacterium autotrophicum and Desulfobacter postgatei was long-lasting. The results indicate that inhibition of SRB by NR-SOB is caused by nitrite production. Nrf-containing SRB can overcome this inhibition by further reducing nitrite to ammonia, preventing a stalling of the favourable metabolic interactions between these two bacterial groups. Nrf, which is widely distributed in SRB, can thus be regarded as a resistance factor that prevents the inhibition of dissimilatory sulphate reduction by nitrite.

Antibiosis↗

PubMedDate not supplied

Butyl nitrite transformation in vitro, chemical nitrosation reactions, and mutagenesis.

The transformation of n-butyl nitrite added to whole blood, plasma, and water was studied using anion exchange high pressure liquid chromatography, spectrometry, and gas chromatography. Butyl nitrite is predominantly converted to butanol, nitrite, and nitrate in acidic water and to butanol, nitrate, and methemoglobin in whole blood; however, butyl nitrite shows little initial conversion to those products in plasma. Thiol nitrosation of plasma proteins was indirectly demonstrated. Chemical nitrosation of cysteine was deduced spectrophotometrically by the interactions of butyl nitrite with cysteine and 5,5'-dithio(bis)2-nitrobenzoic acid (DTNB). Ames test mutagenicity of n-butyl nitrite was confirmed.

Biotransformation↗