Nitrifying bacteria

Nitrifying bacteria are chemoautotrophic or chemolithotrophs depending on the genera (Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrococcus) bacteria that grow by consuming inorganic nitrogen compounds. Many species of nitrifying bacteria have complex internal membrane systems that are the location for key enzymes in nitrification: ammonia monooxygenase which oxidizes ammonia to hydroxylamine, and nitrite oxidoreductase, which oxidizes nitrite to nitrate.

Ecology

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.

Oxidation of ammonia to nitrate

Nitrification in nature is the result of actions of two groups of organisms, the nitrosifyers (ammonia-oxidizing bacteria) and nitrifying bacteria (nitrite-oxidizing, nitrate producing bacteria)

Nitrosifying bacteria

NH₃ + O₂ + 2H⁺ + 2e⁻ → NH₂OH +  H₂O (1.1)

NH₂OH +  H₂O → NO−
2 + 5H⁺ + 4e⁻ (1.2) +

---

NH₃ + O₂ → NO−
2 + 3H⁺ + 2e⁻ (1)

Nitrifying bacteria

NO−
2 +  H₂O → NO−
3 + 2H⁺ + 2e⁻ (2)

Nitrifying bacteria that oxidize ammonia (nitrosifyers) Characteristics Genus Phylogenetic group DNA (mol% GC) Habitats Gram-negative short to long rods, motile (polar flagella)or nonmotile; peripheral membrane systems Nitrosomonas Beta 45-53 Soil, Sewage, freshwater, Marine Large cocci, motile, vesicular or peripheral membranes Nitrosococcus Gamma 49-50 Freshwater, Marine Spirals, motile (peritrichous flagella); no obvious membrane system Nitrosospira Beta 54 Soil Pleomorphic, lobular, compartmented cells; motile (peritrichous flagella) Nitrosolobus Beta 54 Soil

Nitrifying bacteria that oxidize nitrite Characteristics Genus Phylogenetic group DNA (mol% GC) Habitats Short rods, reproduce by budding, occasionally motile (single subterminal flagella) or non-motile; membrane system arranged as a polar cap Nitrobacter Alpha 59-62 Soil, Freshwater, Marine Long, slender rods, nonmotile, no obvious membrane system Nitrospina Delta 58 Marine Large Cocci, motile (one or two subterminal flagellum) membrane system randomly arranged in tubes Nitrococcus Gamma 61 Marine Helical to vibroid-shaped cells; nonmotile; no internal membranes Nitrospira Nitrospirae 50 Marine, Soil

See also

• Root nodule
• Denitrification
• Denitrifying bacteria
• f-ratio
• Nitrification
• Nitrogen cycle
• Nitrogen deficiency
• Nitrogen fixation