Difference Between Nitrifying and Denitrifying Bacteria

Key Difference – Nitrifying vs Denitrifying Bacteria
 

Nitrogen is an essential nutrient for living organisms, and it is of great importance that the available nitrogen is well balanced and recycled in order to be used by living organisms. Nitrogen exists in its natural diatomic form (N₂), which cannot be absorbed by plants for their biological functions. The process of oxidizing fixed diatomic nitrogen into nitrates and nitrites is called nitrification; this is most often done by bacterial species which can utilize nitrogen in its fixed form. In order to maintain the nitrogen balance in the atmosphere, diatomic nitrogen should be produced through a recycling mechanism, where the nitrates and nitrites are reduced back to diatomic nitrogen by bacterial species. This process is termed as denitrification. Thus, bacteria involved in these two processes are characterized as nitrifying bacteria and denitrifying bacteria. The key difference between nitrifying and denitrifying bacteria is that nitrifying bacteria are capable of oxidizing available ammonia to nitrate and nitrite whereas denitrifying bacteria are capable of reducing nitrates and nitrites to its naturally occurring diatomic form nitrogen gas.

CONTENTS

1. Overview and Key Difference
2. What are Nitrifying Bacteria
3. What are Denitrifying Bacteria
4. Similarities Between Nitrifying and Denitrifying Bacteria
5. Side by Side Comparison – Nitrifying vs Denitrifying Bacteria in Tabular Form
6. Summary

What are Nitrifying Bacteria?

Nitrifying bacteria are chemolithotrophic aerobic bacteria that are capable of oxidizing NH₃ in the soil to nitrate or nitrite. NH₃ in soil exists in its ionic form of NH₄⁺. Complete nitrification takes place in two processes, where NH₃ is first oxidized to Nitrite (NO₂^–) followed by Nitrate (NO₃^–), which is utilized by plants.

1. NH₄⁺ + O₂ NO₂^– + H⁺ + H₂O
2. NO₂^–+ O₂ NO₃^–
   

   Figure 01: Nitrogen Cycle

Examples of Nitrifying bacteria which carry out the first reaction of nitrification include Nitrosomonas and Nitrospira which belong to the β subclass of Proteobacteria. Bacteria that are capable of carrying out the second reaction of the nitrification process and produce nitrate include Nitrobacter, which belong to α subclass of Proteobacteria.

What are Denitrifying Bacteria?

Denitrifying bacteria are a type of chemolithotrophic anaerobic or aerobic bacteria that are capable of reducing nitrates and nitrites to gaseous nitrogen forms. The two main forms are diatomic Nitrogen (N₂) and Nitrous oxide (N₂O). Through this process, atmospheric Nitrogen levels are regenerated to the normal concentration. The denitrification reaction is illustrated below.

NO₃^– → NO₂^– → NO + N₂O → N_{2 (g)}

Figure 02: Denitrification

Facultative anaerobes involved in denitrification are Thiobacillus denitrificans, and Micrococcus denitrificans. Pseudomonas denitificans is an aerobic denitrifying bacterium.

What are the Similarities Between Nitrifying and Denitrifying Bacteria?

• Nitrifying and denitrifying bacteria are chemolithoautotrophic.
• Most of them are soil borne bacteria.
• Both groups participate in maintaining the balance of nitrogen in the biosphere
• Both nitrifying and denitrifying bacteria contain enzymes which catalyze the reactions of nitrification and denitrification
• Both nitrifying and denitrifying bacteria are used industries.

What is the Difference Between Nitrifying and Denitrifying Bacteria?

Summary – Nitrifying vs Denitrifying Bacteria

The nitrogen cycle is one of the most important biogeochemical cycles in nature where atmospheric Nitrogen is converted to various chemical forms, making it available for living organisms to utilize. The process of nitrification is an oxidative process where nitrogen present as ammonium in soil is converted to nitrates and nitrites, increasing the bio-availability of nitrogen for organisms. During denitrification, nitrites and nitrates are reduced to gaseous forms (diatomic nitrogen and nitrous oxide). This is the difference between nitrifying and denitrifying bacteria. Both these processes are biologically made favorable by the involvement of microbes, especially chemolithotrophic bacteria. At present, these bacteria are considered as industrially important in the fields of agricultural and environmental biotechnology. Therefore, they have become a potential research topic in the field of Biotechnology.

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References:

1. Cébron, Aurélie, Thierry Berthe, and Josette Garnier. “Nitrification and Nitrifying Bacteria in the Lower Seine River and Estuary (France).” Applied and Environmental Microbiology. American Society for Microbiology, Dec. 2003. Web. Available here. 01 August 2017.
2. Takaya, Naoki, Maria Antonina B. Catalan-Sakairi, Yasushi Sakaguchi, Isao Kato, Zhemin Zhou, and Hirofumi Shoun. “Aerobic Denitrifying Bacteria That Produce Low Levels of Nitrous Oxide.” Applied and Environmental Microbiology. American Society for Microbiology, June 2003. Web. Available here. 01 August 2017.

Image Courtesy:

1. “nitrogen cycle” by KoiQuestion (CC BY-SA 2.0) via Flickr
2. “1.12 Buffers for nitrogen” by National Agroforestry Center (CC BY 2.0) via Flickr

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