Anammox reactions

An important development is the appreciation of the role of anammox bacteria. These carry out the anaerobic reaction between NH4 and NO2 in which nitrite is the electron donor with the production of N2 (Schmid et al. 2005). Several groups of bacteria have been implicated, and all of them belong to the phylum Planctomyces, although quite distinct organisms may be involved. They... 

As we mentioned in Chapter 1, we are unsure of the time of the origin of NO in the atmosphere and hence of the beginnings of oxidative processes in membranes associated with nitrogen oxides. One example is provided by Planctomycetes, the anammox bacteria, which carries out the reaction... 

Recent research suggests that denitrification may involve the reduction of nitrate to nitrite followed by the reaction of nitrite with ammonium in which the nitrogen in nitrite oxidizes the nitrogen in ammonium thereby generating a molecule of NjCg). This is termed the anammox reaction. 

Some of the missing nitrogen is also likely due to the anammox reaction, in which ammonia is oxidized to N2 by anaerobic microbes. 

Recent research has identified some other microbial routes for denitrification that are not heterotrophic. One, called the anammox reaction, involves the oxidation of ammonium to N2 using either nitrite or nitrate as the electron donor. The second has bacteria using Mn " to reduce nitrate to N2. As noted earlier, N2 is generated by the oxidation of ammonium using Mn02 as the electron acceptor. [Denitrification may also be supported by Fe " (aq) oxidation.] These reactions are summarized in Table 12.2. The overall consequence of these reactions is that ammonium does not accumulate in the pore waters where Mn respiration and denitrification are occurring. 

The biogeochemical cycling of nitrogen is very much controlled by redox reactions. This perspective is presented in Figure 24.3 for the redox reactions that take place in the water column and sediments. The major pathways of reduction are nitrogen fixation, assimilatory nitrogen reduction, and denitrification. The major oxidation processes are nitrification and anaerobic ammonium oxidation (anammox). Each of these is described next in further detail. 

The decrease in the sum of nitrate, nitrite, and ammonium that is observed in the 0 = 15.90-16.00kgm-3 density layer is usually explained by denitrification [26,46], consumption by chemosynthesis [23], or/and anammox, the reaction between nitrite and ammonia [47,48]. From the comparison of the vertical gradients (Fig. 3) the role of nitrate becomes comparable with that of oxygen only in the lower part of the redox layer. Nitrate can be consumed for denitrification and reduction by thiosulfate, elemental sulfur, and sulfide [49,50]. The role of nitrate as a potential oxidizer of reduced manganese and iron is actively being discussed now [51], but the presence of these reactions has not been proved or widely accepted. If they exist, these reactions... 

Biomolecules containing [3]- and [5]-ladderanes have been discovered within intracellular hpid membranes of anammox bacteria" that recycle atmospheric nitrogen. The ladderane lipids are found in the membrane surrounding a unique cytoplasmic organelle, the anammoxosome, within which the anaerobic oxidation of ammonia into molecular nitrogen occurs. The oxidation, known as the anammox process, follows the reaction (equation 24) ... 

Dalsgaard, T., Canfield, D. E., Petersen, J., Thamdrup, B., and na Gonzalez, J. A. (2003). N2 production by the anammox reaction in the anoxic water column of Golfo Duke, Costa Rica. 

Additionally, the anammox reaction mentioned earlier results in the reduction of N02 with the production of N2 gas. Recent direct tracer evidence from both marine sediments (Thamdrup and Dalsgaard, 2002) (see Chapter 6, Devol, this volume) and several anoxic water column systems (Hamersley et al., 2007 Kuypers et al., 2005) has shown that the anammox pathway, rather than conventional denitrification, can be a significant and, at times, predominant source of N2 production. Future studies of combined N loss from reefal environments should also consider this pathway. 

Anammox (i.e., anaerobic ammonium oxidation) is a recently discovered process that also results in N2 gas production and so is another form of denitrification (see Chapter 6 by Devol, this volume). The overall anammox reaction is NH4++N02 —> N2+2H2O. To date anammox rates have been quantified using parallel incubations with either N-labeled NH4+ or N-labeled and then analyzing the... 

Ammonium oxidation linked to NO2 (nitrite) reduction was first recognized in a wastewater treatment system and patented under the process name anammox for auaerobic ammonium oxidation (Mulder et al., 1995). The discovery was motivated by observations of simultaneous NH and NO losses balanced by N2 production under anaerobic conditions. The existence of a missing chemolithotrophic organism capable of coupling NH oxidation to either NO or NO2 reduction had been predicted nearly two decades earlier based on thermodynamic considerations (Broda, 1977). The anammox reaction was initially proposed to involve NO (Mulder et al., 1995) ... 

Reactions (16) and (17) were distinguished using an N isotope pairmg technique in which the NFL pool was enriched with while the NOs and NO2 pools remained dominated by " N. With the NFtJ pool dominated by N, reaction (16) yields 75% N2 (i.e., N- N) and 25% whereas reaction (17) yields 100% N2 (van de Graaf et al., 1995, 1997). The anammox process also produces small amounts of NOJ that are thought to provide reducing equivalents for CO2 assimilation (Jetten et al., 1999). 

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