Which microorganisms are primarily responsible for oxidizing ammonium to nitrite and nitrite to nitrate in the nitrogen cycle?

Which microorganisms are primarily responsible for oxidizing ammonium to nitrite and nitrite to nitrate in the nitrogen cycle?

• A. Denitrifying Bacteria
• B. Nitrogen-Fixing Bacteria
• C. Nitrifying Bacteria
• D. Photosynthetic Bacteria

Answer: (C)

Nitrification is the process where certain bacteria gain energy by oxidizing inorganic nitrogen compounds. In the first step, ammonia-oxidizing bacteria convert ammonium (NH4+) to nitrite (NO2−); in the second step, nitrite-oxidizing bacteria convert nitrite to nitrate (NO3−). These two groups together are responsible for turning reduced forms of nitrogen into nitrate that plants can use. They are chemoautotrophs, meaning they obtain energy from chemical reactions (the oxidation of NH3/NH4+ and NO2−) and use CO2 as a carbon source; they require oxygen for the oxidation reactions. This differs from denitrifying bacteria, which reduce nitrate to nitrogen gas under low oxygen conditions; nitrogen-fixing bacteria, which convert N2 into NH3; and photosynthetic bacteria, which rely on light to drive energy for carbon fixation.

Nitrification is the process where certain bacteria gain energy by oxidizing inorganic nitrogen compounds. In the first step, ammonia-oxidizing bacteria convert ammonium (NH4+) to nitrite (NO2−); in the second step, nitrite-oxidizing bacteria convert nitrite to nitrate (NO3−). These two groups together are responsible for turning reduced forms of nitrogen into nitrate that plants can use. They are chemoautotrophs, meaning they obtain energy from chemical reactions (the oxidation of NH3/NH4+ and NO2−) and use CO2 as a carbon source; they require oxygen for the oxidation reactions. This differs from denitrifying bacteria, which reduce nitrate to nitrogen gas under low oxygen conditions; nitrogen-fixing bacteria, which convert N2 into NH3; and photosynthetic bacteria, which rely on light to drive energy for carbon fixation.