What is the Difference Between Nitrosomonas and Nitrobacter

The main difference between Nitrosomonas and Nitrobacter is that Nitrosomonas is responsible for the oxidation of ammonium to nitrite, whereas Nitrobacter converts nitrite to nitrate. 

Nitrosomonas and Nitrobacter are two nitrifying bacteria that are in the nitrogen cycle. They play an essential role in converting nitrogen compounds. 

Key Areas Covered

1. What is Nitrosomonas
– Definition, Facts, Importance
2. What is Nitrobacter
– Definition, Facts, Importance
3. Similarities Between Nitrosomonas and Nitrobacter
– Outline of Common Features
4. Difference Between Nitrosomonas and Nitrobacter
– Comparison of Key Differences

Key Terms 

Nitrobacter, Nitrosomonas 

What is Nitrosomonas

Nitrosomonas is a Gram-negative bacterium that belongs to the family Nitrosomonadaceae. Morphology-wise, it is a genus that contains rod-shaped or ellipsoidal-shaped cells. In addition, the bacterial cells of Nitrosomonas have extensive intracytoplasmic membranes seen as flattened vesicles. Most species include flagellum in the polar region; therefore, Nitrosomonas is motile. Some Nitrosomonas are short rods, rods or contain pointed ends.

Figure 1: Nitrosomonas

Also, Nitrosomonas is an obligate chemolithoautotroph using ammonia as an energy source. It is vital as an ammonia-oxidizing bacteria in the nitrogen cycle. Therefore, it increases the bioavailability of nitrogen in plants. Nitrosomonas is a photophobic bacterium that forms clumps with other microbes or secretes biofilm matrix to avoid light. 

Furthermore, there are two genes involved in nitrification in Nitrosomonas. They are ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO). Two operons encode the genes responsible for the above two enzymes: the amoCAB operon and the hao operon. Further, the first enzyme catalyzes the reaction of converting ammonia into hydroxylamine, and the second enzyme catalyzes the reaction of converting hydroxylamine into nitrite. 

What is Nitrobacter

Nitrobacter is another nitrifying bacterium that belongs to the family Nitrobacteraceae. It is a Gram-negative bacterium that is rod-shaped, pear-shaped, or pleomorphic. The length of the bacterium is 1.0–2.0 μm, and the width is 0.5–0.9 μm. Also, it contains an intra-cytomembrane polar cap. Significantly, Nitrobacter contains cytochromes c. Therefore, it is yellow in suspensions. Importantly, Nitrobacter does not possess flagella, and consequently, it is non-motile. Nitrobacter occurs in soil and marine systems.

Figure 2: Nitrification in Aquatic Environment

Moreover, Nitrobacter undergoes oxidation of nitrite to nitrate. Therefore, nitrite is the energy source of Nitrobacter. It is an essential bacterium in the nitrogen cycle to oxidize nitrites into nitrates. In ocean systems, the production of inorganic nitrogen from the oxidation of nitrite to nitrate is vital to the photosynthetic organism such as phytoplankton. 

Similarities Between Nitrosomonas and Nitrobacter

• Nitrosomonas and Nitrobacter are two nitrifying bacteria in the nitrogen cycle.
• They are essential for the nitrification of ammonia.
• They are chemoautotrophs.
• They occur in the soil and water.
• They are gram-negative rod-shaped bacteria. 

Difference Between Nitrosomonas and Nitrobacter

Definition

Nitrosomonas refers to a genus of spherical to rod-shaped, chemoautotrophic bacteria found in soil and water and obtains energy for growth by oxidizing ammonia to nitrites. In contrast, Nitrobacter, a genus of rod- or pear-shaped nitrifying bacteria occurring in soil, secures energy for growth by oxidizing nitrites to nitrates and growing poorly on organic media.

Family

Nitrosomonas belongs to the family Nitrosomonadaceae, while Nitrobacter belongs to the family Nitrobacteraceae.

Motility

Nitrosomonas is motile while Nitrobacter is non motile.

Function

Nitrosomonas converts ammonia into nitrite, while Nitrobacter converts nitrite into nitrates.     

Examples

N. europea, N. eutropha, N. halophila, and N. mobilis are examples of Nitrosomonas, while N. alkalicus, N. hamburgensis, N. vulgaris, and N. winogradskyi are examples of Nitrobacter. 

Conclusion

In brief, Nitrosomonas and Nitrobacter are two types of nitrifying bacteria in the nitrogen cycle. They are Gram-negative and chemoautotrophs. Nitrosomonas belongs to the family Nitrosomonadaceae. It converts ammonia into nitrite. Examples of Nitrosomonas include N. europea, N. eutropha, N. halophila, and N. mobilis. In comparison, Nitrobacter is another nitrifying bacterium that belongs to the family Nitrobacteraceae. It converted nitrite into nitrates. Examples of Nitrobacter include N. alkalicus, N. hamburgensis, N. vulgaris, and N. winogradskyi. Therefore, the main difference between Nitrosomonas and Nitrobacter is their function. 

References:

1. Nitrosomonas. Nitrosomonas – an overview | ScienceDirect Topics. (n.d.). 
2. Nitrobacter. Nitrobacter – an overview | ScienceDirect Topics. (n.d.). 

Image Courtesy:

1. “Nm-eutropha” By Asw-hamburg – Own work (CC-BY 3.0) via Commons Wikimedia
2. “Aquaponics Nitrogen Cycle” By Friendlyaquaponics – Own Work (CC-BY SA 3.0) via Commons Wikimedia