Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nitrosomonas”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed2001

In situ analysis of Nitrosomonas spp. in wastewater treatment wetland biofilms.

The presence of the ammonia-oxidising group Nitrosomonas in developing biofilms from a subsurface flow dairy effluent treatment wetland was investigated using in situ hybridisation and a crude semi-quantitative PCR. Fluorescently labelled oligonucleotide probes, specific for the Nitrosomonas europaea and Nitrosomonas eutropha species, showed that nitrifying bacteria were present from the onset of biofilm development but that over a five month period the proportions remained low (averaging less than 1% of the total bacterial population). The greatest presence of these nitrifiers was found in the second trench of the subsurface flow wetland. Nitrosomonas were also found to be susceptible to environmental change; adverse environmental conditions, such as low temperatures, coincided with negligible Nitrosomonas presence throughout the wetland. However, during one period of elevated ammonium concentrations Nitrosomonas presence rapidly increased as high as 7% of the total bacterial population. Investigations of relative occurrence of effluent bacterial population of Nitrosomonas europaea and the biofilm populations showed that Nitrosomonas presence in the effluent coincided with significant presence in adjacent biofilms. This suggests seeding between both sessile and planktonic populations of this species. Nitrosomonas occurred as single cells in biofilms throughout the study and were never observed as dense clusters.

Aerobiosis↗
PubMed1983

Proton electrochemical gradients in washed cells of Nitrosomonas europaea and Nitrobacter agilis.

The components of the proton motive force (Deltap), namely, membrane potential (Deltapsi) and transmembrane pH gradient (DeltapH), were determined in the nitrifying bacteria Nitrosomonas europaea and Nitrobacter agilis. In these bacteria both Deltapsi and DeltapH were dependent on external pH. Thus at pH 8.0, Nitrosomonas europaea and Nitrobacter agilis had Deltapsi values of 173 mV and 125 mV (inside negative), respectively, as determined by the distribution of the lipophilic cation [(3)H]tetraphenyl phosphonium. Intracellular pH was determined by the distribution of two weak acids, (14)C-benzoic and (14)C-acetyl salicylic, and the weak base [(14)C]methylamine. Nitrosomonas europaea accumulated (14)C-benzoic acid and (14)C-acetyl salicylic acid when the external pH was below 7.0 and [(14)C]methylamine at alkaline pH. Similarly, Nitrobacter agilis accumulated the two weak acids below an external pH of about 7.5 and [(14)C]methylamine above this pH. As these bacteria grow best between pH 7.5 and 8.0, they do not appear to have a DeltapH (inside alkaline). Thus, above pH 7.0 for Nitrosomonas europaea and pH 7.5 for Nitrobacter agilis, Deltapsi only contributed to Deltap. In Nitrosomonas europaea the total Deltap remained almost constant (145 to 135 mV) when the external pH was varied from 6 to 8.5. In Nitrobacter agilis, Deltap decreased from 178 mV (inside negative) at pH 6.0 to 95 mV at pH 8.5. Intracellular pH in Nitrosomonas europaea varied from 6.3 at an external pH of 6.0 to 7.8 at external pH 8.5. In Nitrobacter agilis, however, intracellular pH was relatively constant (7.3 to 7.8) over an external pH range of 6 to 8.5. In Nitrosomonas europaea, Deltap and its components (Deltapsi and DeltapH) remained constant in cells at various stages of growth, so that the metabolic state of cells did not affect Deltap. Such an experiment was not possible with Nitrobacter agilis because of low cell yields. The effects of protonophores and ATPase inhibitors on DeltapH and Deltapsi in the two nitrifying bacteria are considered.

Hydrogen-Ion Concentration↗
PubMed2006

Stoichiometric and kinetic characterisation of Nitrosomonas sp. in mixed culture by decoupling the growth and energy generation processes.

A novel method that relies on the decoupling of the energy production and biosynthesis processes was used to characterise the maintenance, cell lysis and growth processes of Nitrosomonas sp. A Nitrosomonas culture was enriched in a sequencing batch reactor (SBR) with ammonium as the sole energy source. Fluorescent in situ hybridization (FISH) showed that Nitrosomonas bound to the NEU probe constituted 82% of the bacterial population, while no other known ammonium or nitrite oxidizing bacteria were detected. Batch tests were carried out under conditions that both ammonium and CO2 were in excess, and in the absence of one of these two substrates. The oxygen uptake rate and nitrite production rate were measured during these batch tests. The results obtained from these batch tests, along with the SBR performance data, allowed the determination of the maintenance coefficient and the in situ cell lysis rate, as well as the maximum specific growth rate of the Nitrosomonas culture. It is shown that, during normal growth, the Nitrosomonas culture spends approximately 65% of the energy generated for maintenance. The maintenance coefficient was determined to be 0.14-0.16 mgN mgCOD(biomass)(-1)h(-1), and was shown to be independent of the specific growth rate. The in situ lysis rate and the maximum specific growth rate of the Nitrosomonas culture were determined to be 0.26 and 1.0 day(-1) (0.043 h(-1)), respectively, under aerobic conditions at 30 degrees C and pH 7.

Bioreactors↗
PubMed2006

Effect of free ammonia and free nitrous acid concentration on the anabolic and catabolic processes of an enriched Nitrosomonas culture.

The effects of free ammonia (FA; NH(3)) and free nitrous acid (FNA; HNO(2)) concentrations on the metabolisms of an enriched ammonia oxidizing bacteria (AOB) culture were investigated using a method allowing the decoupling of growth and energy generation processes. A lab-scale sequencing batch reactor (SBR) was operated for the enrichment of an AOB culture. Fluorescent in-situ hybridization (FISH) analysis showed that 82% of the bacterial population in the SBR bound to the NEU probe specifically designed for Nitrosomonas europaea. Batch tests were carried out to measure the oxygen and ammonium consumption rates by the culture at various FA and FNA levels, in the presence or absence of inorganic carbon (CO(2), HCO(3) (-), and CO(3) (2-)). It was revealed that FA of up to 16.0 mgNH(3)-N . L(-1), which was the highest concentration used in this study, did not have any inhibitory effect on either the catabolic or anabolic processes of the Nitrosomonas culture. In contrast, FNA inhibited both the growth and energy production capabilities of the Nitrosomonas culture. The inhibition on growth initiated at approximately 0.10 mgHNO(2)-N . L(-1), and the data suggested that the biosynthesis was completely stopped at an FNA concentration of 0.40 mgHNO(2)-N . L(-1). The inhibition on energy generation initiated at a slightly lower level but the Nitrosomonas culture was still oxidizing ammonia at half of the maximum rate at an FNA concentration of 0.50-0.63 mgHNO(2)-N . L(-1). The affinity constant of the Nitrosomonas culture with respect to ammonia was determined to be 0.36 mgNH(3)-N . L(-1), independent of the presence or absence of inorganic carbon.

Ammonia↗
PubMed1963

Phosphorylation by extracts of Nitrosomonas europaea.

Burge, W. D. (University of California, Berkeley), E. Malavolta, and C. C. Delwiche. Phosphorylation by extracts of Nitrosomonas europaea. J. Bacteriol. 85:106-110. 1963.-Cellfree preparations of Nitrosomonas europaea are capable of oxidizing hydroxylamine, but not ammonium ion, to nitrite. The quantity of nitrite formed by our preparations was, at most, equivalent to only 70% of the hydroxylamine added. Although the preparations had a strong phosphatase activity, resulting in a net loss of organic phosphate during the experimental period, P(32)-labeled inorganic phosphate was found to be incorporated into the organic fraction, including adenosine triphosphate (ATP) and adenosine diphosphate (ADP). The provision of hydroxylamine as substrate resulted in the formation of nitrite and an increased incorporation of P(32) into the organic fraction. It is concluded that the chemosynthetic autotroph Nitrosomonas, in common with certain other autotrophic organisms and heterotrophs, is capable of converting energy released in the oxidation of its inorganic substrate into high-energy phosphate units (ATP and ADP) for the mediation of other energy-requiring reactions. The simultaneous formation of ATP and ADP is interpreted as evidence for an adenylate kinase activity. The preparations used exhibited a considerable endogenous incorporation of P(32) into organic phosphate in the absence of added hydroxylamine. Cyanide inhibited both phosphorylation and the oxidation of hydroxylamine. Both the supernatant and particulate fractions of a Nitrosomonas extract subjected to centrifugal fields of 100,000 x g were active in phosphorylation and nitrite formation, but these activities appeared to be uncoupled in the particulate fraction and only partially coupled in the supernatant solution. This most likely reflects a significant endogenous respiration, and not a real lack of coupling between the two reactions.

Cyanides↗
PubMed2001

Development of nitrification inhibition assays using pure cultures of Nitrosomonas and Nitrobacter.

Restricted requirements for nitrogen reduction at wastewater treatment plants have increased the need for assays determining the inhibition of nitrification. In this paper, two new assays studying ammonia oxidation and nitrite oxidation, respectively, are presented. As test organisms, pure cultures of Nitrosomonas and Nitrobacter isolated from activated sludge are used. The assays are performed in test tubes where the bacteria are incubated with the compound or wastewater to be tested. The nitrification rate is measured during 4 h and compared with reference samples. The test organisms were characterised with respect to temperature, pH and cell activity. Optimum temperature was 35 degrees C for Nitrosomonas and 38 degrees C for Nitrobacter; optimum pH was 8.1 for Nitrosomonas and 7.9 for Nitrobacter. There was a linear relationship between the nitrification rate and the cell concentration in the studied interval. The cell activity decreased slightly with storage time. A significant level of inhibition was calculated to 11% for the Nitrosomonas assay, and to 9% for the Nitrobacter assay. The assays are applicable to determination of nitrification inhibition in samples of industrial waste waters or influents of treatment plants, or chemical substances likely to be found in wastewater.

Ammonia↗
PubMed1998

Recovery of a Nitrosomonas-like 16S rDNA sequence group from freshwater habitats.

In order to study the diversity of ammonia-oxidising bacteria in freshwater habitats, including sediments, a molecular approach focused on the sequencing of 16S rDNA was adopted. 16S rDNA sequences showing affinity with the beta-subgroup of ammonia-oxidising bacteria were recovered by specific PCR of directly isolated DNA from freshwater samples, and samples from brackish water and Glyceria maxima rhizosphere were included in the analysis for comparison. The ammonia oxidiser-like sequences recovered from several locations, which exhibit differences in the composition of their total microbial communities as indicated by denaturing gradient gel electrophoresis, formed a strong monophyletic cluster including Nitrosomonas ureae. This is the first report presenting sequences from an apparently dominant group of Nitrosomonas-like organisms among the beta-subdivision of ammonia-oxidising bacteria in freshwater environments. This group of sequences extends the known diversity within the beta-subgroup of ammonia-oxidisers. The new sequences related to Nitrosomonas ureae do not match with some published primers and probes designed for the detection of Nitrosomonas species, which may explain why these sequences have not previously been detected in freshwater habitats. The sequence diversity detected within this group of sequences was minimal across the environments examined, and no patterns of distribution were indicated with respect to environmental factors such as sediment depth or location.

Base Sequence↗
PubMed1970

Polyphosphate and orthophosphate content of Nitrosomonas europaea as a function of growth.

After inoculation of a stationary-phase culture of Nitrosomonas europaea into fresh growth solution, the cell-associated orthophosphate increased rapidly to 800 mumoles/g (wet weight), whereas the acid-insoluble long-chain polyphosphate content decreased rapidly to 22 mumoles/g. As growth proceeded, the orthophosphate content decreased rapidly to a level of 15 mumoles/g and the long-chain polyphosphate content gradually increased to 60 to 90 mumoles/g. When the pH of a culture of Nitrosomonas decreased during growth below approximately 7.4, the rate of nitrite and polyphosphate synthesis increased and the ratio of change in protein to change in nitrite decreased. When the pH of the culture was maintained above 7.6 throughout growth, polyphosphate accumulation, an increased rate of nitrite and polyphosphate synthesis, and a decreased ratio of change in protein to change in nitrite were not observed. Cells of Nitrosomonas apparently accumulated polyphosphate when adenosine triphosphate generated during the oxidation of ammonia to nitrite was not efficiently used to promote an increase in cell mass. The rapid hydrolysis of polyphosphate after the transfer of stationary-phase cells into fresh growth solution was found to be triggered primarily by the higher pH of the fresh growth solution. The efflux of orthophosphate during culture growth was not associated with a decrease in the pH of the growth solution. Data on the chemical composition of Nitrosomonas are presented.

Adenosine Triphosphate↗
PubMed1982

Respiration-dependent proton translocation in Nitrosomonas europaea and its apparent absence in Nitrobacter agilis during inorganic oxidations.

Oxygen pulse experiments were carried out with the nitrifying bacteria Nitrosomonas europaea and Nitrobacter agilis and with spheroplasts and everted vesicles prepared from Nitrobacter agilis. In addition to thiocyanate, the salting-in anions perchlorate and trichloroacetate proved to be permeant and effective in allowing respiration-dependent proton translocation with Nitrosomonas europaea. Valinomycin-K+, however, was generally ineffective in this respect with Nitrosomonas europaea. The observed leads to H+/O ratio for ammonium ion oxidation by Nitrosomonas europaea was 3.4; that for hydroxylamine and hydrazine cation oxidation was 4.4. These values, when corrected for production of stoichiometric protons and for the fact that the first step in ammonium ion oxidation (hydroxylamine production) is mediated by a monooxygenase, give effective leads to H+/O ratios of about 4 for these three substrates. This value compares favorably with those obtained with other aerobes. No convincing evidence was obtained for operation of a respiratory proton pump in Nitrobacter agilis during nitrite oxidation. Implications of this unexpected result are discussed.

Ammonium Chloride↗
PubMed1983

Methane Oxidation by Nitrosococcus oceanus and Nitrosomonas europaea.

Chemolithotrophic ammonium-oxidizing and nitrite-oxidizing bacteria including Nitrosomonas europaea, Nitrosococcus oceanus, Nitrobacter sp., Nitiospina gracilis, and Nitrococcus mobilis were examined as to their ability to oxidize methane in the absence of ammonium or nitrite. All ammonium oxidizers tested had the ability to oxidize significant amounts of methane to CO(2) and incorporate various amounts into cellular components. None of the nitrite-oxidizing bacteria were capable of methane oxidation. The methane-oxidizing capabilities of Nitrosococcus oceanus and Nitrosomonas europaea were examined with respect to ammonium and methane concentrations, nitrogen source, and pH. The addition of ammonium stimulated both CO(2) production and cellular incorporation of methane-carbon by both organisms. Less than 0.1 mM CH(4) in solution inhibited the oxidation of ammonium by Nitrosococcus oceanus by 87%. Methane concentrations up to 1.0 mM had no inhibitory effects on ammonium oxidation by Nitrosomonas europaea. In the absence of NH(4)-N, Nitrosococcus oceanus achieved a maximum methane oxidation rate of 2.20 x 10 mumol of CH(4) h mg (dry weight) of cells, which remained constant as the methane concentration was increased. In the presence of NH(4)-N (10 ppm [10 mug/ml]), its maximum rate was 26.4 x 10 mumol of CH(4) h mg (dry weight) of cells at a methane concentration of 1.19 x 10 mM. Increasing the methane concentration above this level decreased CO(2) production, whereas cellular incorporation of methane-carbon continued to increase. Nitrosomonas europaea showed a linear response throughout the test range, with an activity of 196.0 x 10 mumol of CH(4) h mg (dry weight) of cells at a methane concentration of 1.38 x 10 mM. Both nitrite and nitrate stimulated the oxidation of methane. The pH range was similar to that for ammonium oxidation, but the points of maximum activity were at lower values for the oxidation of methane.

Journal Article↗
PubMed1999

Construction of a highly bioluminescent Nitrosomonas as a probe for nitrification conditions.

Cloned luciferase-encoding operons were transferred by conjugation to a natural isolate of the ammonia-oxidizing bacterial strain Nitrosomonas sp. RST41-3, thereby establishing conjugation as a tool for gene transfer into Nitrosomonas strains. Luminescence was dependent on the pH of the medium and the concentration of the substrate ammonium chloride. Moreover, the luminescence of the transconjugants was reduced immediately by micromolar concentrations of nitrapyrin and allylthiourea, which are specific inhibitors of nitrification. Our results indicate that luminescent Nitrosomonas strains may be useful as a probe to detect nitrification conditions in the natural environment as well as in sewage plants.

Ammonium Chloride↗
PubMed2001

Crystal structure of Nitrosomonas europaea cytochrome c peroxidase and the structural basis for ligand switching in bacterial di-heme peroxidases.

The crystal structure of the fully oxidized di-heme peroxidase from Nitrosomonas europaea has been solved to a resolution of 1.80 A and compared to the closely related enzyme from Pseudomonas aeruginosa. Both enzymes catalyze the peroxide-dependent oxidation of a protein electron donor such as cytochrome c. Electrons enter the enzyme through the high-potential heme followed by electron transfer to the low-potential heme, the site of peroxide activation. Both enzymes form homodimers, each of which folds into two distinct heme domains. Each heme is held in place by thioether bonds between the heme vinyl groups and Cys residues. The high-potential heme in both enzymes has Met and His as axial heme ligands. In the Pseudomonas enzyme, the low-potential heme has two His residues as axial heme ligands [Fulop et al. (1995) Structure 3, 1225-1233]. Since the site of reaction with peroxide is the low-potential heme, then one His ligand must first dissociate. In sharp contrast, the low-potential heme in the Nitrosomonas enzyme already is in the "activated" state with only one His ligand and an open distal axial ligation position available for reaction with peroxide. A comparison between the two enzymes illustrates the range of conformational changes required to activate the Pseudomonas enzyme. This change involves a large motion of a loop containing the dissociable His ligand from the heme pocket to the molecular surface where it forms part of the dimer interface. Since the Nitrosomonas enzyme is in the active state, the structure provides some insights on residues involved in peroxide activation. Most importantly, a Glu residue situated near the peroxide binding site could possibly serve as an acid-base catalytic group required for cleavage of the peroxide O--O bond.

Amino Acid Sequence↗
PubMed1994

Detection of Nitrosomonas spp. by polymerase chain reaction.

A unique genomic DNA fragment was isolated from Nitrosomonas europaea ATCC 19718. Based on the sequence of this fragment, oligonucleotide primers for polymerase chain reaction amplification were prepared which amplify sequences of 775 and 658 bp. The predicted DNA fragments were both amplified from the genome of N. europaea and a Nitrosomonas spp. isolated from a local oxidation pond. The primers failed to amplify DNA from the genomes of the ammonia oxidiser Nitrosolobous multiformis, the nitrite oxidiser Nitrococcus mobilis as well as from the genomes of other unrelated heterotrophic bacteria. These DNA sequences could be amplified from 0.01 ng of N. europaea genomic DNA or from 100 intact cells, and it was possible to detect Nitrosomonas DNA in a DNA mixture extracted from water samples drawn from a local oxidation pond.

Base Sequence↗
PubMed1999

Phylogenetic differentiation of two closely related Nitrosomonas spp. That inhabit different sediment environments in an oligotrophic freshwater lake.

The population of ammonia-oxidizing bacteria in a temperate oligotrophic freshwater lake was analyzed by recovering 16S ribosomal DNA (rDNA) from lakewater and sediment samples taken throughout a seasonal cycle. Nitrosospira and Nitrosomonas 16S rRNA genes were amplified in a nested PCR, and the identity of the products was confirmed by oligonucleotide hybridization. Nitrosospira DNA was readily identified in all samples, and nitrosomonad DNA of the Nitrosomonas europaea-Nitrosomonas eutropha lineage was also directly detected, but during the summer months only. Phylogenetic delineation with partial (345 bp) 16S rRNA gene sequences of clones obtained from sediments confirmed the fidelity of the amplified nitrosomonad DNA and identified two sequence clusters closely related to either N. europaea or N. eutropha that were equated with the littoral and profundal sediment sites, respectively. Determination of 701-bp sequences for 16S rDNA clones representing each cluster confirmed this delineation. A PCR-restriction fragment length polymorphism (RFLP) system was developed that enabled identification of clones containing N. europaea and N. eutropha 16S rDNA sequences, including subclasses therein. It proved possible to analyze 16S rDNA amplified directly from sediment samples to determine the relative abundance of each species compared with that of the other. N. europaea and N. eutropha are very closely related, and direct evidence for their presence in lake systems is limited. The correlation of each species with a distinct spatial location in sediment is an unusual example of niche adaptation by two genotypically similar bacteria. Their occurrence and relative distribution can now be routinely monitored in relation to environmental variation by the application of PCR-RFLP analysis.

Cloning, Molecular↗
PubMed1969

Biochemical basis of obligate autotrophy in Nitrosomonas europaea.

The specific activities of isocitric dehydrogenase, alpha-ketoglutaric dehydrogenase, succinic dehydrogenase, malic dehydrogenase, and reduced nicotinamide adenine dinucleotide (NADH) oxidase were determined in extracts of Nitrosomonas europaea and compared with the corresponding values for Anacystis nidulans and autotrophically grown Hydrogenomonas eutropha. In common with other obligate autotrophs and in contrast to facultative autotrophs, Nitrosomonas extracts lacked alpha-ketoglutaric dehydrogenase and KCN-sensitive NADH oxidase activity and had low succinic dehydrogenase activity. The Nitrosomonas NADH oxidase appeared to be of the peroxidase type.

Isocitrate Dehydrogenase↗
PubMed1982

O isotope shift in N NMR analysis of biological N-oxidations: H(2)O-NO(2) exchange in the ammonia-oxidizing bacterium Nitrosomonas.

The (18)O/(16)O shifts in (15)N NMR were determined for nitrite (0.13 ppm or 4.2 Hz at 7.05 T) and nitrate (0.056 ppm or 1.7 Hz at 7.05 T) at neutral pH. The technique, which allows clear differentiation between (16)O and (18)O derivatives of (15)N, was used to assess the source of oxygens in nitrite produced by oxidation of ammonia in Nitrosomonas. The two oxygens of nitrite produced by cell-catalyzed oxidation of ammonia or hydroxylamine had the (16)O/(18)O isotope composition of water. Nitrosomonas is shown to catalyze the rapid exchange of oxygen between nitrite and water. The exchange reaction required the concomitant oxidation of ammonia. The amount of nitrite exchanged could exceed the amount of ammonia oxidized by a factor of 3. This exchange explains previous difficulties in the determination of the source of nitrite oxygen in ammonia oxidation. When cells oxidized [(15)N]ammonia in the presence of a great excess of exogenous [(14)N]nitrite, 20% of one oxygen in the resulting [(15)N]nitrite was derived from dioxygen. Dioxygen is apparently the source of at least one oxygen in nitrite produced by Nitrosomonas.

Journal Article↗
PubMed1965

STRUCTURE OF NITROSOCYSTIS OCEANUS AND COMPARISON WITH NITROSOMONAS AND NITROBACTER.

Murray, R. G. E. (University of Western Ontario, London, Ont., Canada), and S. W. Watson. Structure of Nitrosocystis oceanus and comparison with Nitrosomonas and Nitrobacter. J. Bacteriol. 89:1594-1609. 1965.-Nitrosocystis oceanus has distinctive features: the cell wall (overall thickness, 250 A) has an inner triplet structure and a dense enveloping layer; between these lie the "cell-wall organelles" (two or more per cell; plaques about 0.5 mu in diameter and 0.1 mu thick) of unknown function and genesis. The plasma membrane (ca. 80 A) shows rare intrusions that form irregular peripheral vesicles, which appear to form the component lamellae of the "membranous organelle" and probably detach from the periphery. The membranous organelles consist of about 20 vesicles so flattened that the lumen is only 100 A thick. The outer surfaces are in contact and form a triplet structure with an accentuated center line; these lamellae almost traverse the cell, displace the cytoplasm and the nucleoplasms, and form the prominent, seemingly permanent, feature of the cell. Division is constrictive without trace of a septum, and the act of division divides the membranous organelle. No mesosomes appear to be formed. Nitrosomonas europaea shows no sign of a cell-wall organelle or of the outer enveloping layer of wall. The cytoplasm contains intrusive paired lamellae, which might or might not remain connected to the periphery, and they do not fuse or form regular associations. These are thought to be the equivalent of the vesicles in Nitrosocystis but remaining almost parallel and close to the plasma membrane. Nitrobacter agilis has a unique plasma membrane with a (50 A) dense layer applied to the inside of the usual unit membrane. All of the components are represented in the intrusions, which are arranged over and shape the poles of the cells, with close and regular spacing. Each nitrifier was distinctive; in common they have membrane systems which, it is considered, must relate to the specialized mechanisms for acquiring energy adopted by these organisms.

Bacteria↗
PubMed2002

The roles of the three gene copies encoding hydroxylamine oxidoreductase in Nitrosomonas europaea.

The nitrifying bacterium Nitrosomonas europaea contains three copies of the gene (hao) encoding hydroxylamine oxidoreductase (HAO), the second enzyme in the nitrification pathway which oxidizes NH(2)OH to NO(2)(-). The nucleotide sequences of the hao genes differ by only one nucleotide. Two of the three gene copies have identical promoter sequences, while the third promoter has a different nucleotide sequence. Mutant strains with two of the three copies of hao inactivated were created by insertional inactivation, using DNA cassettes containing kanamycin- and gentamycin-resistance genes. All three double-mutant combinations were obtained. These double mutants were phenotypically identical under the conditions tested. Two of these double mutants were similar to wild-type cells or cells having a single hao copy inactivated regarding growth rates or hydroxylamine-dependent O(2) uptake activity, but had only about 50% of the wild-type level of in vitro HAO activity and hao mRNA. The third hao double mutant had an unstable genotype, resulting in recombination of the gentamycin marker into another copy of hao. The N. europaea genomic sequence was recently completed, revealing the locations of the copies of hao and other nitrification genes. Comparison with the arrangement of hao genes in the closely related strain, Nitrosomonas sp. strain ENI-11, showed a similar organization.

Genes, Bacterial↗