Isolated from soil, Paracoccus denitrificans is an alpha-proteobacterium and the model organism for studies of denitrification whereby nitrate is reduced to dinitrogen in a process coupled to energy conservation. Four distinct enzymes are required to complete the process of denitrification with nitrite, nitric oxide and nitrous oxide as discrete intermediates. Thus, denitrification is of intense interest since it can remove nitrogen-containing fertilizer from agricultural soils, aid the remediation of wastewater and, if denitrification is incomplete, produce gases that are potentially damaging to the atmosphere. The enzymes of denitrification in P. denitrificans are studied by Prof. David Richardson, Dr Myles Cheesman, Dr Nick Watmough and Prof. Julea Butt.
P. denitrificans also provides models for the various biochemically and genetically distinct bacterial nitrate reductases that are found, singly or in various combinations, in all proteobacteria. NarGHI, performs the first step in denitrification. Quinol oxidation is coupled to nitrate reduction with the energy released in this process conserved as a transmembrane proton gradient. NapABC also couples quinol oxidation to nitrate reduction but the energy released is dissipated such that NapABC is proposed to play a role in redox balancing during growth on highly reduced carbon substrates. The third nitrate reductase produced by P. denitrificans is located in the cytoplasm and has a role in assimilating inorganic nitrogen, from nitrate, into organic molecules. These enzmes are studied by Prof. David Richardson and Prof. Julea Butt.