Question

In the process of Nitrification, ammonia is first oxidized to nitrite by:
A) Nitrosomonas and Nitrosococcus
B) Nitrosomonas and Nitrobacter
C) Pseudomonas and Nitrosococcus
D) Pseudomonas and thiobacillus

Answer 1

Hint: Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate. The change of ammonia to nitrite is generally the rate limiting step of nitrification. Nitrification is a significant step in the nitrogen cycle in soil.

Complete answer:
Nitrification is an aerobic process performed by little groups of autotrophic microorganisms and archaea. This process was found by the Russian microbiologist Sergei Winogradsky.

The oxidation of ammonia into nitrite is performed by two groups of life forms, ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). AOB can be found among the β-proteobacteria and gamma proteobacteria. In soils the most studied AOB have a place with the genera Nitrosomonas and Nitrosococcus. In spite of the fact that in soils alkali oxidation happens by both AOB and AOA, AOA dominates in both soils and marine conditions.

The second step (oxidation of nitrite into nitrate) is done mainly by microbes such as Nitrobacter and Nitrospira. The two stages are producing energy to be coupled to ATP combination. Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for development. Some AOB have the protein, urease, which catalyzes the change of the urea atom to two ammonia molecules and one carbon dioxide molecule.

Thus, the correct answer is option A, i.e. "Nitrosomonas and Nitrosococcus".

Note:Nitrosomonas europaea, just as populations of soil-abiding AOB, have been appeared to absorb the carbon dioxide delivered by the reaction to make biomass through the Calvin Cycle, and gather energy by oxidizing ammonia (the other products of urease) to nitrite. This feature may clarify enhanced growth of AOB within the presence of urea in acidic conditions.