The key difference between anammox and denitrification is that anammox refers to anaerobic ammonium oxidation, which converts ammonium and nitrites into nitrogen gas under anoxic conditions. Meanwhile,while denitrification is the biological transformation of nitrate into N2 by denitrifying bacteria.
The nitrogen cycle is an important biogeochemical cycle in which nitrogen is converted into different chemical forms such as NH3, NH4+, NO2–, NO3– etc. There are four major processes seen in the nitrogen cycle. They are fixation, ammonification, nitrification, and denitrification. Many of these processes are carried out by microorganisms, especially bacteria present in the soil. Anammox is one of the latest additions to the nitrogen cycle. It is the process of anaerobic ammonium oxidation. A specific group of bacteria known as planctomycetes carry out this process. They possess a special organelle called anammoxosomes, which provide the site for anammox reaction. However, in the end, both denitrification and anammox produce nitrogen gas.
CONTENTS
1. Overview and Key Difference
2. What is Anammox
3. What is Denitrification
4. Similarities Between Anammox and Denitrification
5. Side by Side Comparison – Anammox vs Denitrification in Tabular Form
6. Summary
What is Anammox?
Anammox is a process called anaerobic ammonium oxidation. It is a reaction which uses ammonium and nitrite as the electron acceptors and produces nitrogen gas under anoxic conditions. Anammox reaction is one of the latest additions to the biochemical nitrogen cycle. A specialized group of planctomycete-like bacteria mainly drives it. These bacteria derive their energy for growth from the conversion of ammonium and nitrite into dinitrogen gas in the complete absence of oxygen. They possess one anammoxosome: a membrane-bound compartment inside the cytoplasm that provides the machinery for the anammox process. Moreover, these bacteria are packed with cytochrome c type proteins, including the enzymes that perform the key catabolic reactions of the anammox process, making the cells remarkably red. Anammox bacteria show an extremely slow growth rate.
Figure 01: Anammox
In the marine environment, over 50% of the N2 gas released may be produced by anammox bacteria. Furthermore, the anammox process offers an attractive alternative to current wastewater treatment systems for the removal of ammonia-nitrogen (NH4-N). It also saves ~75% nitrification and 100% denitrification of the nitrogen cycle.
What is Denitrification?
Denitrification is the process of reducing nitrates in the soil into atmospheric nitrogen gas by denitrifying bacteria. It is the opposite of nitrification. Denitrification is an essential step in the nitrogen cycle, which releases fixed nitrogen gas back into the atmosphere and completes the nitrogen cycle.
Figure 02: Denitrification
Denitrification is facilitated by denitrifying bacteria such as Pseudomonas, Clostridium, Thiobacillus denitrificans, Micrococcus denitrificans, etc. These bacteria are facultative anaerobic and heterotrophic bacteria. They work under anaerobic or anoxic conditions like waterlogged soils. They use nitrate as their respiratory substrate, and as a result of it, nitrate is released as gaseous nitrogen to the atmosphere. Likewise, denitrifying bacteria are capable of reducing nitrates and nitrites to its naturally occurring diatomic form nitrogen gas. Through this process, atmospheric Nitrogen levels are regenerated to the normal concentration.
The denitrification reaction is illustrated below.
NO3– → NO2– → NO + N2O → N2 (g)
What are the Similarities Between Anammox and Denitrification?
- Anammox and denitrification are two important parts of the nitrogen cycle.
- These processes produce nitrogen gas.
- Bacteria are the main microorganisms that carry out both processes.
What is the Difference Between Anammox and Denitrification?
Anammox is the anaerobic ammonium oxidation, which is the reaction that converts ammonium and nitrites into nitrogen gas under anoxic conditions. In contrast, denitrification is the reduction of nitrate into gaseous nitrogen by denitrifying bacteria. So, this is the key difference between anammox and denitrification. Besides, anammox process is the reaction of NH4+ + NO2− → N2 + 2H2O, while denitrification is the reaction of NO3– → NO2– → NO + N2O → N2 (g). Therefore, this is another difference between anammox and denitrification.
Moreover, anammox reaction is done by bacteria belonging to planctomycetes (Brocadia, Kuenenia, Anammoxoglobus, Jettenia and Scalindua species). In contrast, denitrification is done by bacteria such as Pseudomonas, Clostridium, Thiobacillus denitrificans, Micrococcus denitrificans, etc. Thus, this is also an important difference between anammox and denitrification.
Summary – Anammox vs Denitrification
Anammox is the reaction which converts ammonium and nitrites into nitrogen gas under anoxic conditions by anammox bacteria, while denitrification is the process of reducing nitrate and nitrite to nitrogen gas by denitrifying bacteria. Both anammox and denitrification are important processes in the biochemical nitrogen cycle. So, this is the summary of the difference between anammox and denitrification.
Reference:
1. Hu, Bao-lan, et al. “Anaerobic Ammonium Oxidation (Anammox) in Different Natural Ecosystems.”Biochemical Society Transactions, U.S. National Library of Medicine, Dec. 2011, Available here.
2. “Denitrification.” Wikipedia, Wikimedia Foundation, 11 Dec. 2019, Available here.
Image Courtesy:
1. “The nitrogen cycle Arrigo” By Shou-Qing Ni and Jian Zhang – Anaerobic Ammonium Oxidation: From Laboratory to Full-Scale Application. BioMed Research International, vol. 2013, pp. 1-10, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Nitrogen Cycle” By Cicle_del_nitrogen_de.svg: *Cicle_del_nitrogen_ca.svg: Johann Dréo (User:Nojhan), traduction de Joanjoc d’après Image:Cycle azote fr.svg.derivative work: Burkhard (talk)Nitrogen_Cycle.jpg: Environmental Protection Agencyderivative work: Raeky (talk) – Cicle_del_nitrogen_de.svgNitrogen_Cycle.jpg (CC BY-SA 3.0) via Commons Wikimedia