Nitrates, reduction to ammonia

Tiedje, ]. M. (1988). Ecology of denitrification and dissimilatory nitrate reduction to ammonia. In Biology of Anaerobic Microorganisms (A. J. B. Zehnder, ed.). pp. 179-244. Wiley, New York. 

Welsh, D. T., CastadeUi, G., Bartoli, M., Poli, D., Careri, M., de Wit, R., and Viaroh, P. (2001). Denitrification in an intertidal seagrass meadow, a comparison of N-isotope and acetylene-block techniques DissimUatory nitrate reduction to ammonia as a source of N2O Mar. Biol. 139, 1029-1036. 

Fazzolari E., Mariotti A., and Germon J. C. (1990) Nitrate reduction to ammonia a dissimilatory process in Enter-obacter amnigenus. Can. J. Microbiol. 36, 779-785. 

Nitrate and nitrite reductases Nitrate reduction to ammonia... 

Dissimilatory Reduction of Nitrate to Ammonium by Microbial Cultures. We studied nitrate reduction to ammonia by an obligate anaerobe, Clostridium, which cannot gain energy from this reduction by electron transport phosphorylation, and by a number of Enterobacteri-aceae (known to be nitrate respirers) that can gain energy via the nitrate to nitrite step. All these organisms converted NOg" to as the... 

N2O Production by Nondenitrifiers During the study of nitrate reduction to ammonia by nitrate-respiring organisms, we noted N2O but not N2 production by all of the cultures listed above except Clostridiurriy which produced no gas. We saw no evidence of further consumption of the N2O. Using as substrate, we evaluated the ratio of... 

FIGURE 8.5 Oxidation and reduction reactions of nitrogen in wetlands. Numbers 1-7 refer to pathways of nitrogen reactions. 1 = ammonification 2 = immobilization 3 = nitrification 4 = denitrification 5 = dissimilatory nitrate reduction to ammonia 6 = dinitrogen fixation and 7 = ammonia volatilization. 

FIGURE 8.48 Effect of sediment depth on partitioning of nitrate reductive processes of denitrification, dissimilatory nitrate reduction to ammonia (DNRA), and assimilatory nitrate reduction (ANR). Each value represents the mean of six relications (D Angelo and Reddy, 1993). 

The existence of reduced volatile phosphorus compounds in aquatic systems has been in question for several decades (Morton and Edwards, 2005). Similar to nitrate reduction to ammonia (dissimi-latory nitrate reduction, see Chapter 8) and sulfate reduction to sulfide, thermodynamic reduction of phosphate to phosphine is possible. Under highly anaerobic conditions, phosphate (oxidation number of +5) can be reduced by obligate anaerobes to phosphine (oxidation number of-3). 

Tiedje, J. M. 1988. Ecology of denitrification and dissimilatory nitrate reduction to ammonia. In A. J. B. 

Fluorides often present surface impurities as residuals from synthesis." Their identification can elucidate the reaction mechanisms in particular, it has been demonstrated by IR spectroscopy that aluminium hydroxy fluorides having the HTB structure contain coordinated or protonated ammonia." Curiously, their synthesis involves a nitrate A1(N03)3,9H20 precursor and ammonia is absent as a reagent. Therefore we have deduced that precursor decomposition implies nitrate reduction to ammonia by isopropanol during the reaction, thus explaining the presence of both ammonia inside the material and acetone... 

The Department of the Environment UK [155] has described a number of alternative methods for the determination of total oxidised nitrogen (nitrate and nitrite) in aqueous solution, while specific methods for nitrate and nitrite are also included. Among the methods for total oxidised nitrogen, one is based on the use of Devarda s alloy for reduction of nitrate to ammonia, and another uses copperised cadmium wire for reducing nitrate to nitrite, which is determined spectrophotometrically. Nitrate may also be determined spectrophotometrically after complex formation with sulfosalicylic acid or following reduction to ammonia, the ammonia is eliminated by distillation and determined titrimetrically. Other methods include direct nitrate determination by ultraviolet spectrophotometry, measurements being made at 210 nm, and the use of a nitrate-selective electrode. Details of the scope, limits of detection, and preferred applications of the methods are given in each case. 

Another approach to the organic nitrogen problem is to use persulfate wet oxidation to convert the nitrogen to nitrate or nitrite, in place of the reduction to ammonia [13,14,24,25]. Results are fully comparable with those from the micro Kjeldahl digestion but the technique is far simpler. The precision should also be higher, since the final step in the measurement, the colorimetric determination of nitrite, is much more precise than any of the ammonia methods. 

Figure 3. The general nitrogen model for illustrating the bio geochemical cycling in Forest ecosystems. Explanations for the fluxes 1, ammonia volatilization 2, forest fertilization 3, N2-fixation 4, denitrification 5, nitrate respiration 6, nitrification 7, immobilization 8, mineralization 9, assimilatory and dissimilatory nitrate reduction to ammonium 10, leaching 11, plant uptake 12, deposition N input 13, residue composition, exudation 14, soil erosion 15, ammonium fixation and release by clay minerals 16, biomass combustion 17, forest harvesting 18, litterfall (Bashkin, 2002).

On the basis of these data, the following mechanism for reduction by hydrogen can be suggested. H2, activated over the Pt sites according to the Pt-catalyzed pathway discussed previously, reduces the stored nitrates directly to ammonia or, more likely, induces the decomposition of nitrates to gaseous NO, which are then reduced by H2 to NH3 over the Pt sites [overall reaction (13.47)]. Once ammonia has been formed, it can react with adsorbed nitrates and this reaction is very selective towards nitrogen. It is worth noting that the reaction of ammonia with NOx obeys the stoichiometry of reaction (13.49), which is different from that of the well-known NH3-NO SCR reaction because it implies the participation of nitrates. 

Ammonia is oxidized in nature to nitrate via several intermediates in the process of nitrification. Nitrate may be reduced to nitrite by either a dissimilatory or an assimilatory process. Nitrite may be assimilated into the cell via reduction to ammonia, or it may be reduced by microorganisms to N20 and N2 in denitrification. A major part of the total nitrogen in this pathway is lost to the atmosphere. However, in turn, atmospheric dinitrogen is converted to ammonia by various bacteria in nitrogen fixation. 

Nitrates and nitrites in water are frequently estimated together, e.g. by reduction to ammonia,1 which can be determined m the manner described below alternative processes are based on the reduction of these salts to nitric oxide which may be measured volumetrically, and on reduction of the nitrate to nitrite when the total nitrite may be estimated eolonmetncaUy by the addition of sulphanihc acid and a-naphthylamine.3 For the estimation of nitrites and mtrates separately, organic colorimetric methods are usually applied.4... 

Cresser, M. S. (1977). Nitrate determination by reduction to ammonia and gas-phase ultraviolet adsorption spectrometry. Analyst 102, 99—103. 

Oxidation of ammonia to nitrite, N02, and nitrate, N03, is called nitrification the reverse reaction is ammonification. Reduction from nitrite to nitrogen is called denitrification. All these reactions, and more, occur in enzyme systems, many of which include transition metals. A molybdenum enzyme, nitrate reductase, reduces nitrate to nitrite. Further reduction to ammonia seems to proceed by 2-electron steps, through an uncertain intermediate with a -fl oxidation state (possibly hyponitrite, N202 ) and hydroxylamine ... 

Barium nitrate is used in certain explosives such as tonitc, and in firework mixtures. It is tested for moisture, insoluble matter, neutrality, chloride, chlorate, sodium, calcium, and lead. On addition of slight excess of sulphuric acid and filtering, the solution should give only traces of residue after evaporation and ignition. The total barium is estimated by the usual methods. The nitrate is best estimated by reduction to ammonia. Barium nitrate may be readily estimated in mixed explosives by extraction with water and precipitation with sulphuric acid. 

Nitrate can also be determined after reduction to ammonia [5]. 

Nitrite has been determined in soil extracts also after the reduction to ammonia [28]. The reactions of nitration have been applied in the determination of nitrate in waters, plants, vegetables, and soil extracts [89,91]. 

Many workers have reported low levels of oxidized nitrogen compounds (that is, nitrite and/or nitrate) along with low levels of ammonia in samples from photosynthesis experiments. As we pointed out in Section III.A, low levels of ammonia can commonly result from contamination, and the oxidized products can then be formed by photooxidation of adventitious ammonia. Alternatively, it is possible that nitrogen is directly photooxidized to nitrite ion (that is, without the prior formation of ammonia) since this reaction is not as thermodynamically daunting as the reduction to ammonia. For example, reaction 16 has AG°(298 K) = 7 kJ. 

The second category includes enzymes that typically catalyze proper oxygen atom transfer reactions to or from an available electron lone pair of a substrate, and can be further subdivided into two families. The first family includes sulfite oxidase and assimilatory nitrate reductase, the physiological functions of which are to reduce nitrate to nitrite in the first stage of its reduction to ammonia for use by the plant cell. The second family comprises bacterial enzymes such as dimethylsulfoxide... 

The nitrate reduction is an important process, since it facilitates the entrance of NO3 into the plant metabolism. The resorbed ammonia nitrogen, urea nitrogen and amino acids can be easily utilized by the plants. Nitrates accepted are used for the synthesis of nitrogen-containing organic substances only after their reduction to ammonia. This reduction is sensitive to the environmental conditions. In the case of a lack of saccharides as energy sources, or if the activity of the reductases is lessened, nitrate nitrogen can be accumulated in plant tissues. 

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