Biological Denitrification.

Denitrification is the biological reduction of nitrogen oxides rather than O₂ during anaerobic and microaerophilic respiratory metabolism. It is an essential component of the Nitrogen Cycle because it is the major route by which inorganic N-oxides in soil return to the atmospheric N pool. Denitrification is environmentally significant because it removes N-oxides from environments that may be adversely affected by excess N, and it produces two trace gases of global significance - NO and N₂O. Denitrification is economically important because it reduces fertilizer N efficiency. Although denitrification has been recognized since the mid 19^th century, key technological developments in gas chromatography and the observation that acetylene (C₂H₂) blocks the final reduction of N₂O to N₂ were required before exponential increases in denitrification research and its quantification could occur. Key regulators of denitrification in soil are O₂, NO₃^-, and C, and analyses of soil denitrification has ranged in scale from enzymatic to global level. Denitrification in soil has proved to be extremely patchy, and variability is high. Because the denitrification pathway is widely distributed among different physiological groups, ecological studies have been hampered by the inability to measure the diversity of denitrifiers using classic microbial culture techniques. Denitrification research has greatly benefited from isolation and characterization of denitrification specific genes – nar, nir, nor, and nos – which have not only clarified the pathway of denitrification  NO₃^- → NO₂^- → NO  → N₂O  → N₂ but have also revealed ecological relationships that were not previously discernible. This poster illustrates several of the key developments in denitrification research with time.