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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Batch experiments were made to better understand the mechanisms of N2O emissions from activated sludge in denitrifying conditions found in urban WWTPs, i.e. under anoxic and low oxygenation conditions. The results showed that in completely anoxic conditions, denitrification, related to a periplasmic nitrate reductase activity, is the major producer of N2O (100% of the N2O production), whereas the nitrate ammonifying activity is not significant. In a gradient of low oxygenation, the highest N2O emissions (49.7+/-3.8 microg N2O-N/g SS/h on average) occurred at a dissolved-oxygen concentration of around 0.3mg O2/L. Below 0.3mg O2/L, heterotrophic denitrification appeared to be the major process responsible for the N2O emission (100% at zero oxygenation). From 0.4 to 1.1mg O2/L, N2O emissions were due to two processes: (i) heterotrophic denitrification that represented about 40% of the N2O production, and (ii) autotrophic nitrifier denitrification that accounted for about 60%. The N2O emissions from activated sludge represented on average 0.4% of reduced NO3(-) in anoxic conditions. The N2O emissions associated with denitrification of entire nitrogen load would amount to 155 T N2O-N/year, if all the Paris wastewater was treated by a process using activated sludge.
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PMID:Nitrous oxide emissions from denitrifying activated sludge of urban wastewater treatment plants, under anoxia and low oxygenation. 1760 59

This paper reviewed the varieties and characteristics of aerobic denitrifiers, their action mechanisms, and the factors affecting aerobic denitrification. Aerobic denitrifiers mainly include Pseudomonas, Alcaligenes, Paracoccus and Bacillus, which are either aerobic or facultative aerobic, and heterotrophic. They can denitrify under aerobic conditions, with the main product being N2O. They can also convert NH4+ -N to gas product. The nitrate reductase which catalyzes the denitrification is periplasmic nitrate reductase rather than membrane-bound nitrate reductase. Dissolved oxygen concentration and C/N ratio are the main factors affecting aerobic denitrification. The main methods for screening aerobic denitrifiers, such as intermittent aeration and selected culture, were also introduced. The research advances in the application of aerobic denitrifiers in aquaculture, waste water processing, and bio-degradation of organic pollutants, as well as the contributions of aerobic denitrifiers to soil nitrogen emission were summarized.
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PMID:[Research advances in aerobic denitrifiers]. 1826 Apr 73

Nitrate respiration catalysed by the epsilon-proteobacterium Wolinella succinogenes relies on the NapAGHBFLD system that comprises periplasmic nitrate reductase (NapA) and various other Nap proteins required for electron transport from menaquinol to NapA or maturation of Nap components. The W. succinogenes Nap system is unusual as electron transfer to NapA was shown previously to depend on both subunits of the predicted menaquinol dehydrogenase complex NapGH but did not require a cytochrome c of the NapC/NrfH family. Nonetheless, minor residual growth by nitrate respiration was observed in napG and napH gene inactivation mutants. Here, the question is addressed whether alternative membrane-bound menaquinol dehydrogenases, like NrfH and NosGH, involved in nitrite or N2O reduction systems, are able to functionally replace NapGH. The phenotypes of various gene deletion mutants as well as strains expressing chimeric nap/nos operons demonstrate that NosH is able to donate electrons to the respiratory chain of nitrate respiration at a physiologically relevant rate, whereas NrfH and NosG are not. The iron-sulphur protein NapG was shown to form a complex with NapH in the membrane but was detected in the periplasmic cell fraction in the absence of NapH. Likewise, NosH is able to bind NapG. Each of the eight poly-cysteine motifs present in either NapG or NapH was shown to be essential for nitrate respiration. The NapG homologue NosG could not substitute for NapG, even after adjusting the cysteine spacing to that of NapG, implying that NapG and NosG are specific adapter proteins that channel electrons into either the Nap or Nos system. The current model on the structure and function of the NapGH menaquinol dehydrogenase complex is presented and the composition of the electron transport chains that deliver electrons to periplasmic reductases for either nitrate, nitrite or N2O is discussed.
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PMID:Characterization of the NapGH quinol dehydrogenase complex involved in Wolinella succinogenes nitrate respiration. 1863 Dec 38

The bc(1) respiratory complex III constitutes a key energy-conserving respiratory electron transporter between complex I (type I NADH dehydrogenase) and II (succinate dehydrogenase) and the final nitrogen oxide reductases (Nir, Nor and Nos) in most denitrifying bacteria. However, we show that the expression of complex III from Thermus thermophilus is repressed under denitrification, and that its role as electron transporter is replaced by an unusual nitrate reductase (Nar) that contains a periplasmic cytochrome c (NarC). Several lines of evidence support this conclusion: (i) nitrite and NO are as effective signals as nitrate for the induction of Nar; (ii) narC mutants are defective in anaerobic growth with nitrite, NO and N2O; (iii) such mutants present decreased NADH oxidation coupled to these electron acceptors; and (iv) complementation assays of the mutants reveal that the membrane-distal heme c of NarC was necessary for anaerobic growth with nitrite, whereas the membrane-proximal heme c was not. Finally, we show evidence to support that Nrc, the main NADH oxidative activity in denitrification, interacts with Nar through their respective membrane subunits. Thus, we propose the existence of a Nrc-Nar respiratory super-complex that is required for the development of the whole denitrification pathway in T. thermophilus.
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PMID:A cytochrome c containing nitrate reductase plays a role in electron transport for denitrification in Thermus thermophilus without involvement of the bc respiratory complex. 1876 83

Wetlands are sources of denitrification-derived nitrous oxide (N2O). Thus, the denitrifier community of an N2O-emitting fen (pH 4.7 to 5.2) was investigated. N2O was produced and consumed to subatmospheric concentrations in unsupplemented anoxic soil microcosms. Total cell counts and most probable numbers of denitrifiers approximated 10(11) cells x g(DW)(-1) (where DW is dry weight) and 10(8) cells x g(DW)(-1), respectively, in both 0- to 10-cm and 30- to 40-cm depths. Despite this uniformity, depth-related maximum reaction rate (v(max)) values for denitrification in anoxic microcosms ranged from 1 to 24 and -19 to -105 nmol N2O h(-1) x g(DW)(-1), with maximal values occurring in the upper soil layers. Denitrification was enhanced by substrates that might be formed via fermentation in anoxic microzones of soil. N2O approximated 40% of total nitrogenous gases produced at in situ pH, which was likewise the optimal pH for denitrification. Gene libraries of narG and nosZ (encoding nitrate reductase and nitrous oxide reductase, respectively) from fen soil DNA yielded 15 and 18 species-level operational taxonomic units, respectively, many of which displayed phylogenetic novelty and were not closely related to cultured organisms. Although statistical analyses of narG and nosZ sequences indicated that the upper 20 cm of soil contained the highest denitrifier diversity and species richness, terminal restriction fragment length polymorphism analyses of narG and nosZ revealed only minor differences in denitrifier community composition from a soil depth of 0 to 40 cm. The collective data indicate that the regional fen harbors novel, highly diverse, acid-tolerant denitrifier communities capable of complete denitrification and consumption of atmospheric N2O at in situ pH.
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PMID:Association of novel and highly diverse acid-tolerant denitrifiers with N2O fluxes of an acidic fen. 2002 77

Nitrification inhibitors exert inhibition function in soil nitrification process (NH4(+)-N to NO3(-)-N) and are widely applied in order to improve N fertilizer use efficiency. Before the new nitrification inhibitor is used, its effects on denitrification process must be investigated and denitrifying enzyme activity (DEA) is an effective indicator to show this process. In the present paper, a mass spectrometery (MS) method was taken to measure the denitrifying enzyme activity in the new nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) incubation system. The results showed that the method measured the concentration of N2O in the incubation system accurately and the concentration measured by MS had marked correlation with that measured by gas chromatogram (GC) (MS(N2O) = -0.45 + 1.03GC(N2O, R2 = 0.995). At the same time, enrichment of 15 N2O and 15 N2 was measured to discriminate the nitrate reductase and N2O reductase. Differed with traditional method, the enzymatic inhibitor-acetylene was not appended. The results showed that DMPP had no influence on the denitrifying enzyme activity and indicated that the denitrification process was not influenced by DMPP.
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PMID:[Mass spectrometry assay for denitrifying enzyme activity measurement]. 2082 21

To understand the mechanisms underlying the increased N2O reductase activity in the Bradyrhizobium japonicum 5M09 mutant from enrichment culture under N2O respiration, we analyzed the expression of genes encoding denitrification reductases and regulators. Our results suggest a common regulation of nap (encoding periplasmic nitrate reductase) and nos (encoding N2O reductase).
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PMID:Linked expressions of nap and nos genes in a Bradyrhizobium japonicum mutant with increased N(2)O reductase activity. 2362 75

Denitrifiers differ in how they handle the transition from oxic to anoxic respiration, with consequences for NO and N2O emissions. To enable stringent comparisons we defined parameters to describe denitrification regulatory phenotype (DRP) based on accumulation of NO2(-) , NO and N2O, oxic/anoxic growth and transcription of functional genes. Eight Thauera strains were divided into two distinct DRP types. Four strains were characterized by a rapid, complete onset (RCO) of all denitrification genes and no detectable nitrite accumulation. The others showed progressive onset (PO) of the different denitrification genes. The PO group accumulated nitrite, and no transcription of nirS (encoding nitrite reductase) was detected until all available nitrate (2 mM) was consumed. Addition of a new portion of nitrate to an actively denitrifying culture of a PO strain (T. terpenica) resulted in a transient halt in nitrite reduction, indicating that the electron flow was redirected to nitrate reductase. All eight strains controlled NO at nano-molar concentrations, possibly reflecting the importance of strict control for survival. Transient N2O accumulation differed by two orders of magnitude between strains, indicating that control of N2O is less essential. No correlation was seen between phylogeny (based on 16S rRNA and functional genes) and DRP.
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PMID:Strains in the genus Thauera exhibit remarkably different denitrification regulatory phenotypes. 2366 91

Benthic invertebrates affect microbial processes and communities in freshwater sediment by enhancing sediment-water solute fluxes and by grazing on bacteria. Using microcosms, the effects of larvae of the widespread midge Chironomus plumosus on the efflux of denitrification products (N2O and N2+N2O) and the diversity and abundance of nitrate- and nitrous-oxide-reducing bacteria were investigated. Additionally, the diversity of actively nitrate- and nitrous-oxide-reducing bacteria was analyzed in the larval gut. The presence of larvae increased the total effluxes of N2O and N2+N2O up to 8.6- and 4.2-fold, respectively, which was mostly due to stimulation of sedimentary denitrification; incomplete denitrification in the guts accounted for up to 20% of the N2O efflux. Phylotype richness of the nitrate reductase gene narG was significantly higher in sediment with than without larvae. In the gut, 47 narG phylotypes were found expressed, which may contribute to higher phylotype richness in colonized sediment. In contrast, phylotype richness of the nitrous oxide reductase gene nosZ was unaffected by the presence of larvae and very few nosZ phylotypes were expressed in the gut. Gene abundance of neither narG, nor nosZ was different in sediments with and without larvae. Hence, C. plumosus increases activity and diversity, but not overall abundance of nitrate-reducing bacteria, probably by providing additional ecological niches in its burrow and gut.
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PMID:Chironomus plumosus larvae increase fluxes of denitrification products and diversity of nitrate-reducing bacteria in freshwater sediment. 2405 96

To investigate the impact of experimental warming on N2O emission from soil of soybean field, outdoor experiments with simulating diurnal warming were conducted, and static dark chamber-gas chromatograph method was used to measure N2O emission fluxes. Results indicated that: the diurnal warming did not change the seasonal pattern of N2O emissions from soil. In the whole growing season, comparing to the control treatment (CK), the warming treatment (T) significantly enhanced the N2O flux and the cumulative amount of N2O by 17.31% (P = 0.019), and 20.27% (P = 0.005), respectively. The significant correlations were found between soil N2O emission and soil temperature, moisture. The temperature sensitivity values of soil N2O emission under CK and T treatments were 3.75 and 4.10, respectively. In whole growing stage, T treatment significantly increased the crop aboveground and total biomass, the nitrate reductase activity, and total nitrogen in leaves, while significantly decreased NO3(-) -N content in leaves. T treatment significantly increased soil NO3(-) -N content, but had no significant effect on soil organic carbon and total nitrogen contents. The results of this study suggested that diurnal warming enhanced N2O emission from soil in soybean field.
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PMID:[Effects of diurnal warming on soil N2O emission in soybean field]. 2419 36


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