Understanding Bacteria That Oxidize Ammonia into Nitrite

The process of converting ammonia ($\text{NH}_3$) or ammonium ions ($\text{NH}_4^+$) into nitrite ($\text{NO}_2^-$) is the first step in nitrification. This process is primarily carried out by a specific group of bacteria known as ammonia-oxidizing bacteria (AOB). These bacteria are crucial players in the nitrogen cycle, transforming nitrogen from one form to another in soil and aquatic environments.

The Process of Ammonia Oxidation

Oxidation of ammonia involves the following chemical reaction, mediated by enzymes within these bacteria:

$\text{NH}_3 \rightarrow \text{NH}_2\text{OH} \rightarrow \text{NO}_2^-$

This transformation is performed by bacteria that gain energy from this oxidation process. They are typically chemoautotrophs, meaning they use inorganic compounds for energy and carbon dioxide as their carbon source.

Key Bacteria Involved in Ammonia Oxidation

Several genera of bacteria are known to oxidize ammonia into nitrite. Some of the prominent ones include:

• Nitrosomonas
• Nitrosococcus
• Nitrosospira
• Nitrosolobus
• Nitrosovibrio

These are the bacteria that oxidize ammonia into nitrite, performing the critical initial step of nitrification.

Distinguishing Ammonia Oxidizers from Nitrite Oxidizers

It's important to differentiate between bacteria that oxidize ammonia into nitrite and those that oxidize nitrite into nitrate. The second step of nitrification, converting nitrite ($\text{NO}_2^-$) to nitrate ($\text{NO}_3^-$), is carried out by a different group of bacteria, known as nitrite-oxidizing bacteria (NOB).

Common examples of nitrite-oxidizing bacteria include:

• Nitrobacter
• Nitrococcus (note: there are different species, some classified as AOB like Nitrosococcus, others as NOB. The context of the question points to Nitrococcus in the AOB group).
• Nitrospira

Nitrobacter is a well-known example of a bacterium that oxidizes nitrite to nitrate, completing the nitrification process.

Looking at the options provided, we are asked to identify which bacteria oxidizes ammonia into nitrite. The options are Nitrococcus, Nitrobacter, or both. As discussed, Nitrobacter primarily oxidizes nitrite to nitrate. Nitrococcus, particularly some species, is a bacterium that oxidizes ammonia into nitrite.

Therefore, the bacterium that oxidizes ammonia into nitrite among the given choices is Nitrococcus.