Which two bacteria are involved in the two-step nitrification process in aquatic systems?

Which two bacteria are involved in the two-step nitrification process in aquatic systems?

• A. Nitrosomonas and Nitrobacter
• B. Nitrosomonas and Thiobacillus
• C. Nitrobacter and Thiobacillus
• D. Chlorobium and Nitrosomonas

Answer: (A)

Nitrification in aquatic systems is driven by two distinct groups of chemoautotrophic bacteria working in sequence. Ammonia-oxidizing bacteria, such as Nitrosomonas, convert ammonia (NH3/NH4+) into nitrite (NO2−). Then nitrite-oxidizing bacteria, such as Nitrobacter, take that nitrite and oxidize it to nitrate (NO3−). This two-step chain is essential for nitrogen cycling and helps prevent buildup of toxic ammonia or nitrite. The other organisms listed do not participate in this canonical two-step nitrification: thiobacilli are primarily sulfur-oxidizers, chlorobium is a photosynthetic bacterium, and neither forms the complementary pair needed to convert ammonia to nitrate.

Nitrification in aquatic systems is driven by two distinct groups of chemoautotrophic bacteria working in sequence. Ammonia-oxidizing bacteria, such as Nitrosomonas, convert ammonia (NH3/NH4+) into nitrite (NO2−). Then nitrite-oxidizing bacteria, such as Nitrobacter, take that nitrite and oxidize it to nitrate (NO3−). This two-step chain is essential for nitrogen cycling and helps prevent buildup of toxic ammonia or nitrite.

The other organisms listed do not participate in this canonical two-step nitrification: thiobacilli are primarily sulfur-oxidizers, chlorobium is a photosynthetic bacterium, and neither forms the complementary pair needed to convert ammonia to nitrate.