Nitrogen cycle ammonification

The involvement of HA during bacterial conversion of nitrate to NH3 (known also as the nitrate ammonification phase of the nitrogen cycle) has been studied at the molecular level as part of an effort to delineate the mechanism of conversion of nitrite to NH3 by a group of multiheme cytochromes of bacterial origin. The overall reduction reaction is depicted in equation 3 for cytochrome c-nitrite reductase " ... 

Figure 21.1 Microbial nitrogen cycling processes in sedimentary environments on a coral reef (A) nitrogen fixation (B) ammonification (C) nitrification (D) dissimilatory nitrate reduction and denitrification (E) assimilatory nitrite/nitrate reduction (F) ammonium immobilization and assimilation. Adapted from D Elia and Wiebe (1990). Anammox (the anaerobic oxidation of NH4" with NO2 yielding N2 ) is not represented, as it has not yet been shown to occur on coral reefs, but may be found to be important in reef sediments.

For the most part, nitrogen cycles within the ocean have the same microbial processes as in the soil (Figure 1). BNF is the dominant source of new nitrogen to the ocean, with other smaller contributions coming from atmospheric deposition and riverine runoff. Ammonification, nitrification, uptake, and decomposition are all critical components. There are two primary removal mechanisms—denitrification and burial in marine... 

Fig. 3.17 Summary of the nitrogen cycle (oxidation states of nitrogen shown in parentheses). Ammonium assimilation and ammonification can occur in oxic and anoxic environments, as can nitrogen fixation (although the most prolific bacteria are aerobes).

Figure 2 Stepwise decomposition of particulate organic nitrogen (PON) in arbitrary units versus time during a dark incubation. Nitrogen is transformed, first to NH4+ by bacterial ammonification and finally to NOa and NOs by the two-step process of bacterial nitrification. These same processes are responsible for the global ocean formation of NOs in the deep sea. These data are the idealized results of pioneering nitrogen cycle investigators, T. von Brand and N. Rakestraw, who unraveled these processes more than 50 years ago.

Figure 10.5 Major processes involved in the biogeochemical cycling of N in estuaries and the coastal ocean (1) biological N2 fixation (2) ammonia assimilation (3) nitrification (4) assimilatory NC>3 reduction (5) ammonification or N remineralization (6) ammonium oxidation (speculative at this time) (7) denitrification and dissimilatory NO3 reduction to NH4+ and (8) assimilation of dissolved organic nitrogen (DON). (Modified from Libes, 1992.)...

Such biochemical process of removing nitrogen from the bio-geo-chemical cycle is called ammonification. In the presence of ammonium is repidly oxidized with the participation of microorganisms to nitrate NO. This biochemical process of oxidizing ammonia is called nitrification. Autotrophic nitrification has 2 stages. First, bacteria of genera Nitrosomonas, Nitrosospira, Nitrosococcus, Nitrosolobus form nitrite ... 

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