Experiment 11: Nitrification by Soil Microorganisms

What is nitrification?

Conversion of ammonia to nitrate.

• oxidation rxn

How is conversion of ammonia to nitrate carried out?

• occurs in 2 steps.

• Carried out by 2 genera of bacteria

  • Nitrosomonas

  • Nitrobacter

Reaction Mechanism

NH4+ —> NO2- —> NO3-

Ammonium ion Nitrosomonas. Nitrite ion. Nitrobacter Nitrate ion

Characteristics of Nitrosomonas and Nitrobacter

• Autotrophic

• Appear to be principal organism in soil that can perform nitrification rxns

• Small

• Gram negative

• rods

• Grow best in completely inorganic medium using CO2 as carbon source

What is the nitrate formed as a result of nitrification used for?

Usable form of nitrogen from which plants make proteins.

What would a negative result for both nitrite and ammonia tests suggest about the nitrification activity in the soil sample?

Ammonia-oxidizing bacteria fail to convert ammonia to nitrite, it suggests a lack of active nitrifiers, toxic soil conditions, or environmental limitations

What is the relationship between nitrification and other soil processes like oxidation?

Nitrification is a two-step microbial oxidation process that requires plenty of oxygen