What is the Difference Between Nitrifying and Denitrifying Bacteria

The main difference between nitrifying and denitrifying bacteria is that nitrifying bacteria oxidize ammonia to nitrite and then it is further oxidized to nitrate, whereas denitrifying bacteria reduce nitrate back to nitrogen.

Nitrifying and denitrifying bacteria are two types of bacteria that undergo two processes of the nitrogen cycle: nitrification and denitrification. The nitrogen cycle is important in bringing the inert nitrogen from the air into the biochemical process in plants and then to animals.

Key Areas Covered

1. What are Nitrifying Bacteria
   • Definition, Characteristics, Importance
2. What are Denitrifying Bacteria
   • Definition, Characteristics, Importance
3. Similarities Between Nitrifying and Denitrifying Bacteria
   • Outline of Common Features
4. Difference Between Nitrifying and Denitrifying Bacteria
   • Comparison of Key Differences

Key Terms

Denitrifying Bacteria, Nitrifying Bacteria

What are Nitrifying Bacteria  

Nitrifying bacteria are the microorganisms in the nitrogen cycle, converting the most reduced form of soil nitrogen, ammonia, into its most oxidized form, nitrate. They are also chemolithotrophic organisms that generate energy from the oxidation of inorganic nitrogen compounds. For instance, Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira, and Nitrococcus are nitrifying bacteria. Moreover, there are two types of nitrifying bacteria: they are ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). Moreover, one of the characteristic features of nitrifying bacteria is that they contain a complex internal membrane system required for the enzymatic reactions of nitrification.

Figure 1: Ammonia Oxidation

Furthermore, the common nitrifying pathway is the oxidizing of the ammonia to hydroxylamine by the enzyme, ammonia monooxygenase; oxidization of hydroxylamine into nitric acid by the enzyme, hydroxylamine oxidoreductase; further oxidization of nitrite into nitrate by the enzyme nitrite oxidoreductase.

What are Denitrifying Bacteria

Denitrifying bacteria are the bacteria in the denitrification part of the nitrogen cycle. The main function of denitrifying bacteria is to reduce nitrates back to nitrogen. Moreover, denitrifying bacteria widely occurs in soils and sediments, using oxidized nitrogen compounds as their terminal electron acceptor in the energy production in the absence of oxygen. However, nitrogen oxides are converted into nitrogen gas and nitrous oxide gas by using various enzymes.

Figure 2: Pseudomonas stutzeri

Moreover, around 250 species of denitrifying bacteria occur in over 50 genera and these denitrifying bacteria represent 10-15% of the bacteria population in water, soil, and sediment. Pseudomonas, Alcaligenes, and Bacillus are some examples of denitrifying bacteria.  

Similarities Between Nitrifying and Denitrifying Bacteria

• Nitrifying and denitrifying bacteria are two types of bacteria involved in the oxidation and reduction of nitrogen, respectively.
• They occur in the nitrogen cycle.
• Moreover, they mainly occur in the soil.
• Both nitrification and denitrification are enzymatic reactions.

Difference Between Nitrifying and Denitrifying Bacteria

Definition

Nitrifying bacteria refers to any of various soil bacteria that change ammonia or ammonium into nitrite or change nitrite into nitrate as part of the nitrogen cycle, while denitrifying bacteria refers to microorganisms whose action results in the conversion of nitrates in the soil to free atmospheric nitrogen, thus depleting soil fertility.

Significance

Usually, nitrifying bacteria oxidize ammonium ions into nitrites and nitrates while denitrifying bacteria reduce nitrogen oxides into nitrogen gas and nitrous oxide.

Examples

Some examples of nitrifying bacteria include Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira, and Nitrococcus while some examples of denitrifying bacteria include Pseudomonas, Alcaligenes, and Bacillus.

Soil Fertility

Nitrifying bacteria increase soil fertility while denitrifying bacteria decrease soil fertility.

Conclusion

In brief, nitrifying bacteria are microorganisms that oxidize ammonium into nitrites and nitrates. Therefore, nitrifying bacteria are of two types: AOB and NOB. Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira, and Nitrococcus are nitrifying bacteria. Denitrifying bacteria, on the other hand, are microorganisms that reduce nitrogen oxides into nitrogen gas and nitrous oxide. Pseudomonas, Alcaligenes, and Bacillus are denitrifying bacteria. In conclusion, the main difference between nitrifying and denitrifying bacteria is their type of chemical reactions.

References:

1. Wikimedia Foundation. (2022, June 18). Nitrifying bacteria. Wikipedia. Retrieved September 7, 2022.
2. Wikimedia Foundation. (2022, July 31). Denitrifying bacteria. Wikipedia. Retrieved September 7, 2022.

Image Courtesy:

1. “Ammonia oxidation” By Uswbios – Own Work (CC BY-SA 3.0) via Commons Wikimedia
2. “Pseudomonas stutzeri” By שועל- Own Work (CC BY-SA 3.0) via Commons Wikimedia