Nitrifying bacteria are widespread in soil and water, and are found in highest numbers where considerable amounts of ammonia are present (areas with extensive protein decomposition, and sewage treatment plants).
Nitrifying bacteria thrive in lakes and streams with high inputs of sewage and wastewater because of the high ammonia content.
Cyanobacteria (red algae) inhabit nearly all illuminated environments on Earth and play key roles in the carbon and nitrogen cycle of the biosphere. Generally, cyanobacteria are able to utilize a variety of inorganic and organic sources of combined nitrogen, like nitrate, nitrite, ammonium, urea or some amino acids.
Several cyanobacterial strains are also capable of diazotrophic growth.
Genome sequencing has provided a large amount of information on the genetic basis of nitrogen metabolism and its control in different cyanobacteria. Comparative genomics, together with functional studies, has led to a significant advance in this field over the past years. 2-oxoglutarate has turned out to be the central signaling molecule reflecting the carbon/nitrogen balance of cyanobacteria.
Central players of nitrogen control are the global transcriptional factor NtcA, which controls the expression of many genes involved in nitrogen metabolism, as well as the PII signaling protein, which fine-tunes cellular activities in response to changing C/N conditions.
These two proteins are sensors of the cellular 2-oxoglutarate level and have been conserved in all cyanobacteria.
In contrast, the adaptation to nitrogen starvation involves heterogeneous responses in different strains.
Nitrogen fixation by cyanobacteria in coral reefs can fix twice the amount of nitrogen than on land – around 1.8kg of nitrogen is fixed
Examples of major changes include a disease treatment with antibiotics or chemicals that are harmful to the nitrifying bacteria.