N is the most abundant gas of the atmosphere. It is an important component of the amino acids & nucleic acids.

N is naturally converted to ammonia by lightning.

Chemoautotrophs: Bacteria that obtain their ATP energy by oxidizing inorganic molecules. (Examples: The bacteria that perform nitrogen fixation, nitrification & denitrification in the table below.

A. Nitrogen Fixation:

Conversion of atmospheric N2 into ammonia (NH3). Occurs by lightning, or bacteria in soil or roots of legumes.

B. Nitrification:

Conversion of ammonia by bacteria first to nitrite (NO2) , then into nitrate (NO3). Requires oxygen in soil.

C. Ammonification:

Saprotrophs convert the amino & nucleic acids of dead organisms back to ammonia.

D. Denitrification:

Conversion of nitrate in water-logged (oxygen poor) soil back to atmospheric N2.

An abundance of inorganic nitrogen (as ammonia, nitrite or nitrate) creates problems within the environment as pollutants. During hot summers, the oxygen content of water decreases. Nitrogen remains as ammonia, which is toxic to creatures. In addition, the pH of water increases (ammonia is a weak base).

During cooler weather, an over abundance of nitrates or nitrites creates problems. Plants will use these nutrients to grow and reproduce, often forming algal blooms. If the oxygen content of the water is low, the algae and aquatic plants die creating a stinky mess, and potentially killing fish and other animals. The aquatic food chain thus collapses dramatically! Such overabundance and thus rapid death of algae due to nutrient pollution is known as eutrophication.

Atmospheric Nitrogen: N2

Ammonia: NH3

Nitrite: NO2

Nitrate: NO3

Amino Acids: A.A.

Nucleic Acids: N.A.

[Specific Roles of Bacteria in the Nitrogen Cycle] ------------ [Chemoautotrophy]