The Nitrogen cycle and Nitrogen fixation
The Nitrogen cycle and Nitrogen fixation

Uncle Darwin's Desktop

Of related interest:
The 3 Domains of Life


Organisms depend on many mineral and elemental nutrients for growth, among which is nitrogen that is required in vast amounts. Nitrogen is a primary atom in proteins, nucleic acids and cellular structures that are fundamental to life on earth. While Earth’s atmosphere is some 79% nitrogen, the triple bonded and inert gas is not directly utilizable by organisms. To be used for growth, it first must be "fixed" (or combined) as ammonium (NH4) or nitrate (NO3) ions. Available nitrogen is can be the growth-limiting factor in some ecosystems. Microorganisms are paramount in the Earth’s nitrogen cycle by provided the vast majority of the nitrogen on which life depends. Some bacteria convert N2 into ammonia through a process known as nitrogen fixation. Some bacteria do so through their independent metabolic machinery, and others do so in symbiotic relations with plants or other organisms, of which termites and protozoa are often cited examples. Additionally, decomposition processes by some bacteria results in the release of usable forms of nitrogen.

Van de Pas-Schoonen KT, Schalk-Otte S, Haaijer S, Schmid M, Op den Camp H, Strous M, Gijs Kuenen J, Jetten MS Complete conversion of nitrate into dinitrogen gas in co-cultures of denitrifying bacteria. Biochem Soc Trans. 2005 Feb;33(Pt 1):205-9. [Pubmed]

Philippot L Tracking nitrate reducers and denitrifiers in the environment. Biochem Soc Trans. 2005 Feb;33(Pt 1):200-4. [Pubmed]