Nitrification microbiology: which bacterial genus listed below is known to oxidize ammonia (NH4+/NH3) to nitrite in the first step of nitrification?

Introduction / Context:
Nitrification proceeds in two steps: ammonia oxidation to nitrite, then nitrite oxidation to nitrate. Correctly identifying the taxa responsible for each step is essential in environmental engineering, wastewater treatment, and soil ecology.

Given Data / Assumptions:

• We focus on the ammonia-oxidizing step (AOB), not nitrite oxidizers (NOB).
• Classic AOB genera include Nitrosomonas, Nitrosococcus, and Nitrosospira.
• Classic NOB genera include Nitrobacter, Nitrospira, and Nitrospina.

Concept / Approach:
Ammonia-oxidizing bacteria convert NH3/NH4+ to NO2− via ammonia monooxygenase and hydroxylamine oxidoreductase. Among the options, only Nitrosococcus is a recognized ammonia oxidizer. The others listed primarily oxidize nitrite to nitrate (NOB) or are misapplied names.

Step-by-Step Solution:

Verification / Alternative check:
Microbial ecology literature consistently places Nitrosococcus among ammonia oxidizers, especially in marine systems.

Why Other Options Are Wrong:

• A/B/E: Nitrospina, Nitrobacter, and Nitrospira are nitrite oxidizers (second step).
• D: “Nitrosobacter” is not the standard recognized genus; likely a confusion with Nitrosomonas/Nitrosospira.

Common Pitfalls:
Confusing the two steps of nitrification or generalizing that all “Nitro-” genera do the same task; prefixes reflect different roles.

Final Answer:
Nitrosococcus