Nitrosomonas bacteria break down ____________ into _____________ in an aquarium or aquaponics system

• A. ammonia (NH3); Nitrites (NO2)
• B. ammonia (NH3); nitrates (NO3)
• C. nitrites (NO2); nitrates (NO3)
• D. carbon dioxide (CO2); nitrates (NO3)

Answer: (A)

Nitrosomonas bacteria perform the first step of nitrification by oxidizing ammonia into nitrite. In an aquarium or aquaponics system, fish waste and decomposing matter produce ammonia (NH3, which can exist in equilibrium with NH4+). Nitrosomonas use oxygen to convert that ammonia into nitrite (NO2−), which is still toxic at high levels and must be processed further. The next bacteria, such as Nitrobacter, then convert nitrite into nitrate (NO3−), which is less toxic and can be used by plants or removed by water changes. The other options don’t fit this organism’s role: turning nitrite into nitrate is done by a different group of bacteria; producing nitrate directly from ammonia isn’t how this first step works; and carbon dioxide is not part of this nitrification process.