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PubMed1978

Effects of low concentrations of bisulfite-sulfite and nitrite on microorganisms.

A wide range of microorganisms was tested to determine their sensitivity to low concentrations of bisulfite-sulfite and nitrite, solubility products of SO2 and NO2, respectively. Photosynthesis by blue-green algae (cyanobacteria) was more strongly inhibited by 0.1 mM bisulfite-sulfite and 1 mM nitrite at pH 6.0 than photosynthesis by eucaryotic algae and respiration of bacteria, fungi, and protozoa. At pH 7.7, blue-green algae were still more sensitive to bisulfite-sulfite and nitrite than eucaryotic algae, but the toxicity of bisulfite-sulfite and nitrite decreased as the pH increased. Photosynthesis by Anabaena flos-aquae at pH 6.0 was inhibited 25% by a bisulfite-sulfite concentration of 10 micrometer and 15% by a nitrite concentration of 50 micrometer. Photosynthesis by the blue-green alga, Lyngbya sp., was not exceptionally sensitive to chlorate and thiosulfate. Acetylene-reducing activity of Beijerinckia indica was completely inhibited by 0.1 mM bisulfite-sulfite at pH 4.0, the suppression being decreased with increasing pH.

Animals↗

PubMed1980

Bacterial inhibitory effects of nitrite: inhibition of active transport, but not of group translocation, and of intracellular enzymes.

Nitrite inhibited active transport of proline in Escherichia coli but not group translocation of sugar via the phosphoenolpyruvate:phosphotransferase system. These results were consistent with previous results that nitrite inhibits active transport, oxygen uptake, and oxidative phosphorylation in aerobic bacteria. Nitrite also inhibited aldolase (EC 4.1.2.13) from E. coli, Pseudomonas aeruginosa, Streptococcus faecalis, and rabbit muscle. Thus, these various data showed that nitrite has more than one site of attack in the bacterial cell. These data also indicated that nitrite is inhibitory to a wide range of physiological types of bacteria.

Biological Transport, Active↗

PubMed2001

Dissimilatory nitrite reductase genes from autotrophic ammonia-oxidizing bacteria.

The presence of a copper-containing dissimilatory nitrite reductase gene (nirK) was discovered in several isolates of beta-subdivision ammonia-oxidizing bacteria using PCR and DNA sequencing. PCR primers Cunir3 and Cunir4 were designed based on published nirK sequences from denitrifying bacteria and used to amplify a 540-bp fragment of the nirK gene from Nitrosomonas marina and five additional isolates of ammonia-oxidizing bacteria. Amplification products of the expected size were cloned and sequenced. Alignment of the nucleic acid and deduced amino acid (AA) sequences shows significant similarity (62 to 75% DNA, 58 to 76% AA) between nitrite reductases present in these nitrifiers and the copper-containing nitrite reductase found in classic heterotrophic denitrifiers. While the presence of a nitrite reductase in Nitrosomonas europaea is known from early biochemical work, preliminary sequence data from its genome indicate a rather low similarity to the denitrifier nirKs. Phylogenetic analysis of the partial nitrifier nirK sequences indicates that the topology of the nirK tree corresponds to the 16S rRNA and amoA trees. While the role of nitrite reduction in the metabolism of nitrifying bacteria is still uncertain, these data show that the nirK gene is present in closely related nitrifying isolates from many oceanographic regions and suggest that nirK sequences retrieved from the environment may include sequences from ammonia-oxidizing bacteria.

Amino Acid Sequence↗

PubMed2002

Nitrite as a stimulus for ammonia-starved Nitrosomonas europaea.

Ammonia-starved cells of Nitrosomonas europaea are able to preserve a high level of ammonia-oxidizing activity in the absence of ammonium. However, when the nitrite-oxidizing cells that form part of the natural nitrifying community do not keep pace with the ammonia-oxidizing cells, nitrite accumulates and may subsequently inhibit ammonia oxidation. The maintenance of a high ammonia-oxidizing capacity during starvation is then nullified. In this study we demonstrated that cells of N. europaea starved for ammonia were not sensitive to nitrite, either when they were starved in the presence of nitrite or when nitrite was supplied simultaneously with fresh ammonium. In the latter case, the initial ammonia-oxidizing activity of starved cells was stimulated at least fivefold.

Ammonia↗

PubMed2006

Genome sequence of the chemolithoautotrophic nitrite-oxidizing bacterium Nitrobacter winogradskyi Nb-255.

The alphaproteobacterium Nitrobacter winogradskyi (ATCC 25391) is a gram-negative facultative chemolithoautotroph capable of extracting energy from the oxidation of nitrite to nitrate. Sequencing and analysis of its genome revealed a single circular chromosome of 3,402,093 bp encoding 3,143 predicted proteins. There were extensive similarities to genes in two alphaproteobacteria, Bradyrhizobium japonicum USDA110 (1,300 genes) and Rhodopseudomonas palustris CGA009 CG (815 genes). Genes encoding pathways for known modes of chemolithotrophic and chemoorganotrophic growth were identified. Genes encoding multiple enzymes involved in anapleurotic reactions centered on C2 to C4 metabolism, including a glyoxylate bypass, were annotated. The inability of N. winogradskyi to grow on C6 molecules is consistent with the genome sequence, which lacks genes for complete Embden-Meyerhof and Entner-Doudoroff pathways, and active uptake of sugars. Two gene copies of the nitrite oxidoreductase, type I ribulose-1,5-bisphosphate carboxylase/oxygenase, cytochrome c oxidase, and gene homologs encoding an aerobic-type carbon monoxide dehydrogenase were present. Similarity of nitrite oxidoreductases to respiratory nitrate reductases was confirmed. Approximately 10% of the N. winogradskyi genome codes for genes involved in transport and secretion, including the presence of transporters for various organic-nitrogen molecules. The N. winogradskyi genome provides new insight into the phylogenetic identity and physiological capabilities of nitrite-oxidizing bacteria. The genome will serve as a model to study the cellular and molecular processes that control nitrite oxidation and its interaction with other nitrogen-cycling processes.

Bacterial Proteins↗

PubMed1975

Growth of Staphylococcus and Salmonella on frankfurters with and without sodium nitrite.

Conventional and nitrite-free frankfurters in loosely wrapped packages were compared as to their ability to support growth of Salmonella, Staphylococcus, and their naturally occurring spoilage flora at 7 C (simulating refrigerated storage) and 20 C (simulating possible temperature abuse). At 7 C Salmonella did not grow in either type of frankfurter; Staphylococcus and the natural spoilage flora sometimes grew more rapidly in the absence of nitrite, but the difference was not significant. At 20 C growth of Salmonella, Staphylococcus, and of the spoilage flora was, at most, only slightly faster on nitrite-free frankfurters. Salmonella was not suppressed in broth culture experiments the pH and nitrite content found in frankfurters. Although either type of frankfurter can become hazardous due to growth of Salmonella or Staphylococcus, no unusual or additional hazard resulted from the omission of nitrite from frankfurters.

Cell Count↗

PubMed1980

Inhibition, but not uncoupling, of respiratory energy coupling of three bacterial species by nitrite.

The effect of nitrite on respiratory energy coupling of three bacteria was studied in light of a recent report that nitrite acted as an uncoupling agent with Paracoccus denitrificans grown under denitrifying conditions. Our determinations of proton translocation stoichiometry of Pseudomonas putida (aerobically grown), Pseudomonas aeruginosa, and P. denitrificans (grown both aerobically and under denitrifying conditions) showed nitrite inhibition of proton-to-oxidant stoichiometry, but not uncoupling. Nitrite both reduced the H+/O ratio and decreased the rate of proton resorption. Increased proton resorption rates, characteristic of authentic uncoupling agents, were not observed. The lack of enhanced proton permeability due to nitrite was verified via passive proton permeability assays. The H+/O ratio of P. aeruginosa increased when growth conditions were changed from aerobic to denitrifying. This suggested the induction of an additional coupling site in the electron transport chain of denitrifying P. aeruginosa.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗

PubMed1986

Short-term nitrate (nitrite) inhibition of nitrogen fixation in Azotobacter chroococcum.

Nitrate-grown Azotobacter chroococcum ATCC 4412 cells lack the ability to fix N2. Nitrogenase activity developed after the cells were suspended in a combined nitrogen-free medium and was paralleled by a concomitant decrease in nitrate assimilation capacity. In such treated cells exhibiting transitory nitrate assimilation and N2-fixation capacity, nitrate or nitrite caused a short-term inhibitory effect on nitrogenase activity which ceased once the anion was exhausted from the medium. The analog L-methionine-DL-sulfoximine, an inhibitor of glutamine synthetase, prevented inhibition of nitrogenase activity by nitrate or nitrite without affecting the uptake of these antions, which were reduced and stoichiometrically released into the external medium as ammonium. Inhibition of nitrogenase by nitrate (nitrite) did not take place in A. chroococcum MCD1, which is unable to assimilate either. We conclude that the short-term inhibitory effect of nitrate (nitrite) on nitrogenase activity is due to some organic product(s) formed during the assimilation of the ammonium resulting from nitrate (nitrite) reduction.

Azotobacter↗

PubMed1990

Localization of the cytochrome cd1 and copper nitrite reductases in denitrifying bacteria.

The locations of cytochrome cd1 nitrite reductases in Pseudomonas aeruginosa and Pseudomonas fluorescens and copper nitrite reductases in Achromobacter cycloclastes and Achromobacter xylosoxidans were identified. Immunogold labeling with colloidal-gold probes showed that the nitrite reductases were synthesized exclusively in anaerobically grown (denitrifying) cells. Little immunogold label occurred in the cytoplasm of these four strains; most was found in the periplasmic space or was associated with cell membranes. Immunogold labeling of thin sections was superior to fractionation by osmotic shock for locating nitrite reductases. The results support models of dentrification energetics that require a periplasmic, not a cytoplasmic, location for nitrite reductases.

Alcaligenes↗

PubMed1993

Structures of genes nasA and nasB, encoding assimilatory nitrate and nitrite reductases in Klebsiella pneumoniae M5al.

Klebsiella pneumoniae can use nitrate and nitrite as sole nitrogen sources during aerobic growth. Assimilatory nitrate and nitrite reductases convert nitrate through nitrite to ammonium. We report here the molecular cloning of the nasA and nasB genes, which encode assimilatory nitrate and nitrite reductase, respectively. These genes are tightly linked and probably form a nasBA operon. In vivo protein expression and DNA sequence analysis revealed that the nasA and nasB genes encode 92- and 104-kDa proteins, respectively. The NASA polypeptide is homologous to other prokaryotic molybdoenzymes, and the NASB polypeptide is homologous to eukaryotic and prokaryotic NADH-nitrite reductases. The narL gene product positively regulates expression of the structural genes for respiratory nitrate reductase, narGHJI. Surprisingly, we found that the nasBA operon is tightly linked to the narL-narGHJI region in K. pneumoniae, even though the nitrate assimilatory and respiratory enzymes serve different physiological functions.

Amino Acid Sequence↗

PubMed1998

Nitrite-specific active transport system of the cyanobacterium Synechococcus sp. strain PCC 7942.

Studies on the nitrite uptake capability of a mutant of Synechococcus sp. strain PCC 7942 lacking the ATP-binding cassette-type nitrate-nitrite-bispecific transporter revealed the occurrence of a nitrite-specific active transport system with an apparent Km (NO2-) of about 20 microM. Similar to the nitrate-nitrite-bispecific transporter, the nitrite-specific transporter was reversibly inhibited by ammonium in the medium.

Biological Transport, Active↗

PubMed1998

NasFED proteins mediate assimilatory nitrate and nitrite transport in Klebsiella oxytoca (pneumoniae) M5al.

Klebsiella oxytoca can use nitrate and nitrite as sole nitrogen sources. The enzymes required for nitrate and nitrite assimilation are encoded by the nasFEDCBA operon. We report here the complete nasFED sequence. Sequence comparisons indicate that the nasFED genes encode components of a conventional periplasmic binding protein-dependent transport system consisting of a periplasmic binding protein (NasF), a homodimeric intrinsic membrane protein (NasE), and a homodimeric ATP-binding cassette (ABC) protein (NasD). The NasF protein and the related NrtA and CmpA proteins of cyanobacteria contain leader (signal) sequences with the double-arginine motif that is hypothesized to direct prefolded proteins to an alternate protein export pathway. The NasE protein and the related NrtB and CmpB proteins of cyanobacteria contain unusual variants of the EAA loop sequence that defines membrane-intrinsic proteins of ABC transporters. To characterize nitrate and nitrite transport, we constructed in-frame nonpolar deletions of the chromosomal nasFED genes. Growth tests coupled with nitrate and nitrite uptake assays revealed that the nasFED genes are essential for nitrate transport and participate in nitrite transport as well. Interestingly, the delta nasF strain exhibited leaky phenotypes, particularly at elevated nitrate concentrations, suggesting that the NasED proteins are not fully dependent on the NasF protein.

ATP-Binding Cassette Transporters↗

PubMed1999

The napF and narG nitrate reductase operons in Escherichia coli are differentially expressed in response to submicromolar concentrations of nitrate but not nitrite.

Escherichia coli synthesizes two biochemically distinct nitrate reductase enzymes, a membrane-bound enzyme encoded by the narGHJI operon and a periplasmic cytochrome c-linked nitrate reductase encoded by the napFDAGHBC operon. To address why the cell makes these two enzymes, continuous cell culture techniques were used to examine napF and narG gene expression in response to different concentrations of nitrate and/or nitrite. Expression of the napF-lacZ and narG-lacZ reporter fusions in strains grown at different steady-state levels of nitrate revealed that the two nitrate reductase operons are differentially expressed in a complementary pattern. The napF operon apparently encodes a "low-substrate-induced" reductase that is maximally expressed only at low levels of nitrate. Expression is suppressed under high-nitrate conditions. In contrast, the narGHJI operon is only weakly expressed at low nitrate levels but is maximally expressed when nitrate is elevated. The narGHJI operon is therefore a "high-substrate-induced" operon that somehow provides a second and distinct role in nitrate metabolism by the cell. Interestingly, nitrite, the end product of each enzyme, had only a minor effect on the expression of either operon. Finally, nitrate, but not nitrite, was essential for repression of napF gene expression. These studies reveal that nitrate rather than nitrite is the primary signal that controls the expression of these two nitrate reductase operons in a differential and complementary fashion. In light of these findings, prior models for the roles of nitrate and nitrite in control of narG and napF expression must be reconsidered.

Culture Media↗

PubMed1999

Signal-dependent phosphorylation of the membrane-bound NarX two-component sensor-transmitter protein of Escherichia coli: nitrate elicits a superior anion ligand response compared to nitrite.

The Nar two-component regulatory system, consisting of the dual sensor-transmitters NarX and NarQ and the dual response regulators NarL and NarP, controls the expression of various anaerobic respiratory pathway genes and fermentation pathway genes. Although both NarX and NarQ are known to detect the two environmental signals nitrate and nitrite, little is known regarding the sensitivity and selectivity of ligand for detection or activation of the sensor-transmitters. In this study, we have developed a sensitive anion-specific in vitro assay for NarX autophosphorylation by using Escherichia coli membranes highly enriched in the full-length NarX protein. In this ATP- and magnesium-dependent reaction, nitrate elicited a greater signal output (i.e., NarX autophosphorylation) than did nitrite. Nitrate stimulation occurred at concentrations as low as 5 microM, and the half-maximal level of NarX autophosphorylation occurred at approximately 35 microM nitrate. In contrast, nitrite-dependent stimulation was detected only at 500 microM, while 3.5 mM nitrite was needed to achieve half-maximal NarX autophosphorylation. Maximal nitrate- and nitrite-stimulated levels of NarX phosphorylation were five and two times, respectively, over the basal level of NarX autophosphorylation. The presence of Triton X-100 eliminated the nitrate-stimulated kinase activity and lowered the basal level of activity, suggesting that the membrane environment plays a crucial role in nitrate detection and/or regulation of kinase activity. These results provide in vitro evidence for the differential detection of dual signaling ligands by the NarX sensor-transmitter protein, which modulates the cytoplasmic NarX autokinase activity and phosphotransfer to NarL, the cognate response regulator.

2,4-Dinitrophenol↗

PubMed1999

The blue copper-containing nitrite reductase from Alcaligenes xylosoxidans: cloning of the nirA gene and characterization of the recombinant enzyme.

The nirA gene encoding the blue dissimilatory nitrite reductase from Alcaligenes xylosoxidans has been cloned and sequenced. To our knowledge, this is the first report of the characterization of a gene encoding a blue copper-containing nitrite reductase. The deduced amino acid sequence exhibits a high degree of similarity to other copper-containing nitrite reductases from various bacterial sources. The full-length protein included a 24-amino-acid leader peptide. The nirA gene was overexpressed in Escherichia coli and was shown to be exported to the periplasm. Purification was achieved in a single step, and analysis of the recombinant Nir enzyme revealed that cleavage of the signal peptide occurred at a position identical to that for the native enzyme isolated from A. xylosoxidans. The recombinant Nir isolated directly was blue and trimeric and, on the basis of electron paramagnetic resonance spectroscopy and metal analysis, possessed only type 1 copper centers. This type 2-depleted enzyme preparation also had a low nitrite reductase enzyme activity. Incubation of the periplasmic fraction with copper sulfate prior to purification resulted in the isolation of an enzyme with a full complement of type 1 and type 2 copper centers and a high specific activity. The kinetic properties of the recombinant enzyme were indistinguishable from those of the native nitrite reductase isolated from A. xylosoxidans. This rapid isolation procedure will greatly facilitate genetic and biochemical characterization of both wild-type and mutant derivatives of this protein.

Alcaligenes↗

PubMed2003

A mutant of Paracoccus denitrificans with disrupted genes coding for cytochrome c550 and pseudoazurin establishes these two proteins as the in vivo electron donors to cytochrome cd1 nitrite reductase.

In Paracoccus denitrificans, electrons pass from the membrane-bound cytochrome bc(1) complex to the periplasmic nitrite reductase, cytochrome cd(1). The periplasmic protein cytochrome c(550) has often been implicated in this electron transfer, but its absence, as a consequence of mutation, has previously been shown to result in almost no attenuation in the ability of the nitrite reductase to function in intact cells. Here, the hypothesis that cytochrome c(550) and pseudoazurin are alternative electron carriers from the cytochrome bc(1) complex to the nitrite reductase was tested by construction of mutants of P. denitrificans that are deficient in either pseudoazurin or both pseudoazurin and cytochrome c(550). The latter organism, but not the former (which is almost indistinguishable in this respect from the wild type), grows poorly under anaerobic conditions with nitrate as an added electron acceptor and accumulates nitrite in the medium. Growth under aerobic conditions with either succinate or methanol as the carbon source is not significantly affected in mutants lacking either pseudoazurin or cytochrome c(550) or both these proteins. We concluded that pseudoazurin and cytochrome c(550) are the alternative electron mediator proteins between the cytochrome bc(1) complex and the cytochrome cd(1)-type nitrite reductase. We also concluded that expression of pseudoazurin is mainly controlled by the transcriptional activator FnrP.

Anaerobiosis↗

PubMed1961

Formation of nitrite and nitrate by actinomycetes and fungi.

Hirsch, P. (Cornell University, Ithaca, New York), L. Overrein, and M. Alexander. Formation of nitrite and nitrate by actinomycetes and fungi. J. Bacteriol. 82:442-448. 1961.-Nitrite was produced by strains of Mycobacterium, Nocardia, Streptomyces, Micromonospora, and Streptosporangium in media containing ammonium phosphate as the sole nitrogen source. The quantity of nitrite formed was small, and the concentration was affected by pH and by the relative levels of carbon and nitrogen. Aspergillus flavus produced little nitrite from ammonium but formed in excess of 100 parts per million of nitrate-nitrogen. Peroxidase activity and heterotrophic nitrification were reduced in acid conditions, but mycelial development of the fungus was not markedly affected. The inability of A. flavus to form nitrate and nitrite at low pH appears to result from a selective effect of pH upon nitrification rather than being a consequence of the decomposition of nitrogenous intermediates.

Actinobacteria↗

PubMed1967

Spectrophotometric and kinetic study of nitrite and formate oxidation in Nitrobacter winogradskyi.

The reduction levels of cytochrome c and a(1) in intact Nitrobacter cells and cell-free extracts, during and after nitrite or formate oxidation, were examined in combination with the amperometric measurement of oxygen uptake. Quite different reduction patterns were observed when comparing nitrite oxidation by intact cells and cell-free extracts. An inverse relationship was observed between the rate of electron flow and the steady-state reduction level of cytochrome a(1). Parallel observations on nitrite oxidation, by use of formate and reduced nicotinamide adenine dinucleotide as electron donors, showed the influence of the high oxidation-reduction potential of the nitrite-nitrate system on cytochrome reduction. A value for the apparent activation energy of the overall nitrite oxidation process, amounting to 15 kcal, was found in a study of the temperature dependence of cytochrome reduction.

Cytochromes↗