Dissimilatory nitrate 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. 

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). 

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

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).

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. 

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... 

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. 

As noted in Section 62.1.9.6, reduction of nitrate may occur by assimilatory or dissimilatory pathways. In the former case, the nitrate produced is reduced further to ammonia, which is incorporated into the cell. In the latter case, nitrate is reduced anaerobically to nitrite, serving as an electron acceptor in the respiration of facultative or a few obligate anaerobic bacteria. The example of Escherichia coli has been considered in Section 62.1.13.4.3. This process is usually terminated at nitrite, which accumulates around the cells, but may proceed further1511 as nitrite-linked respiration in the process of denitrification. 

Cole, J. A., 1988, Assimilatory and dissimilatory reduction of nitrate to ammonia, Symp. Soc. Gen. Microbiol. 42 2819329. 

Nitrate reductases are found in a wide range of eukaryotes and prokaryotes and have a crucial role in nitrogen assimilation and dissimilation (see Chapter 8.14). These enzymes catalyze the reaction shown in Equation (5) for the assimilatory nitrate reductases, this is followed by the reduction of nitrite to ammonia. Dissimilatory nitrate reductases [142 147] catalyze the reduction of nitrate to nitrite for respiration, to generate a transmembrane potential gradient.The assimilatory nitrate reductases have a molybdenum center similar to that of sulfite oxidase (see... 

Dissimilatory reduction of nitrate to ammonia is performed by obligate and facultative anaerobes with fermentative metabolism, including Clostridium and Bacillus species (Tiedje, 1988). These organisms, in contrast to denitrifiers, usually do not rely on nitrate as electron acceptor. Therefore, DNRA involves 8e transfer as compared to 5e transfer for denitrification, suggesting that more organic substrate can be potentially degraded by DNRA. However, nitrate availability under DNRA conditions is usually very low because much of the nitrate formed during nitrification under aerobic conditions is rapidly consumed by denitrifiers in adjacent anaerobic environments. 

A number of different enzymes can carry out the reduction of nitrite to either ammonium or nitric oxide and/or nitrous oxide. The latter types are involved with the denitrification process (Payne, 1973) and will not be considered here. Among the enzymes that catalyze the six-electron reduction of nitrite to ammonia, several different types are recognized. These are (I) assimilatory NiRs that function in biosynthetic nitrate assimilation of higher plants, algae, and fungi, (2) ammonia-forming dissimilatory NiRs involved in anaerobic nitrate respiration of diverse bacteria, and (3) assimilatory and dissimilatory sulfite reductases... 

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