Denitrification facultative

Denitrification is a process in which facultative organisms will reduce nitrate to nitrogen gas in the absence of molecular oxygen. This consequendy results in the removal of BOD. The denitrification process also generates one hydroxyl ion so that alkalinity requirements are reduced to half when both nitrification and denitrification are practiced. 

The best example for facultative anaerobic autotrophic respiration is represented by Thiobacillus denitrificans, as shown in the denitrification reaction g ... 

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. 

Denitrification The reduction of nitrates to nitrites and finally to nitrous oxide or even to molecular nitrogen catalyzed by facultative aerobic soil bacteria working under anaerobic conditions. 

Seventeen genera of facultative anaerobic bacteria (e.g., Pseudomonas and Bacillus) can perform denitrification under anaerobic or low-oxygen conditions, where they use NO3- as an electron acceptor during anaerobic respiration (Jaffe, 2000). In fact, in many estuaries, denitrification is limited by the availability of NC>3 (Koike and Sprensen, 1988 Cornwell et al., 1999). Sources of NC>3 and NC>2 for denitrification are from diffusive inputs from the overlying water column and nitrification in the sediments (Jenkins and Kemp, 1984). The activity of other bacterial processes under anoxic conditions has been shown to affect the activity of denitrifying bacteria. For example, SO42- reduction occurs in anoxic sediments whereby SC>42 is reduced to sulfide (Morse et al., 1992)—more... 

Nearly all heterotrophic denitrifiers are facultative anaerobes (Tiedje, 1988). Although various workers defined suboxia differently, the upper limit of oxygen concentration for the occurrence of denitrification is probably 5 pM, with quantitatively most denitrification in the marine environment taking place below about 2 pM (Cline and Richards, 1972 Codispoti et al., 2005 Devol, 1978 Murray et al., 1995). The ability to denitrify is not limited to the bacteria, archea and even some fungi are capable of denitrification (Knowles, 1996 Zumft and Korner, 1997). 

Canonical denitrifiers are mainly facultative anaerobes that can modify their electron transport system to accommodate N-oxides as the terminal electron acceptor for organic carbon oxidation. However, commitment with the oxidation of proteins to CO2 and H2O is the liberation of the amino group as NH " ". Thus, canonical denitrification should be accompanied by the build up of NH " " concentrations, but... 

There are two pathways of dissimilatory nitrate reduction, generally thought to be mediated by anaerobic, or facultatively anaerobic bacteria, using NOs" as a terminal electron acceptor in respiration (Fig. 21.ID and F) (see Chapter 6, Devol, this volume). One pathway leads to production of ammonium, and may act as an internal cychng loop within the system (D Elia and Wiebe, 1990). The other pathway, denitrification, ends in production of N2O and/or N2 gas, which can then be lost from the system to the atmosphere. 

Denitrification starts when oxygen is almost depleted (below the oxygen penetration depth) by inducing an enzymatic system of nitrate reductase and nitrite reductase by facultative aerobic bacteria, which can only use nitrogenous oxides if oxygen is - nearly - absent. Measurements carried... 

The ability to carry out denitrification is known among.a broad range of facultative anaerobic and anaerobic bacteria such as Pseudomonas. Denitrification requires a source of carbon, and methanol is often used for this... 

Many facultative heterotrophic bacteria (e.g.. Pseudomonas, Micrococcus, Denitrobacillus, Spirillium, Achromo-bacter, etc.) are capable of denitrification. Denitrification takes place under anaerobic conditions, a precondition for the formation of a nitrate-reducing enzyme system. 

Many different groups of bacteria, including Bacillus, Pseudomonas, and Thiobacillus, are capable of denitrification. The primary biochemical pathways for organic substrate oxidation by denitri-fiers are similar to that described for aerobic catabolism. Because most of the denitrifiers are facultative anaerobes, they possess a functional TCA cycle that allows them to metabolize substrates completely to carbon dioxide and water. Many denitrifiers do not produce extracellular enzymes required for hydrolysis of polymers thus, they generally rely on hydrolytic enzymes and fermenters to provide readily available substrates (Ljundahl and Erickson, 1985). 

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. 

Denitrification (mediated by aerobic bacteria capable of anaerobic growth with oxidized nitrogenous compounds, also known as facultative bacteria)... 

Each step of the denitrification pathway is catalyzed by a distinct enzyme, nitrogen oxide reductase (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase), that transfers electrons from the chain to the particular intermediate. Thermodynamically, in the absence of oxygen, nitrogen oxides are the most preferred electron acceptors by facultative bacterial groups. The role of nitrogen oxides in regulating organic matter decomposition has been discussed in earlier chapters (see Chapter 5). 

As the content of fixed nitrogen in ground water is small and at denitrification it is expended much sooner than O, Eh value rapidly declines with the beginning of this process (Figure 2.78). Finally, with sufficient amount of organic matter completely disappears, and Eh value drops below 0.1 V (pe 1.7). This transition uses facultative anaerobics and microaerophiles, which convert available oxidized forms of nitrogen, iron and manganese (NOj , Fe, Mn +) into reduced ones (NH, NH +,N2, Fe +, Mn ). 

Different taxonomic groups are involved in denitrification including Gram negative and positive bacteria. Their remarkable characteristic is their facultative respiration. Some of... 

Denitrification occurs due to the action of facultative anaerobic heterocrophic microorganisms that get their nourishment from an organic substrate and use the oxygen from nitrates. 

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