Table 1.

The genes and enzymes that carry out the bacterial nitrogen cycle.

transformation	genes	encoding enzyme	references
N2 → NH3	nifHDK	nitrogenase	[13]
	narG	dissimilatory nitrate reductase	[14]
	nirS, nirK	nitrite reductase haem cd1 and copper nitrite reductase	[15]
NO → N2O	norCB	nitric oxide reductase	[16,17]
N2O → N2	nosZ	nitrous oxide reductase	[18–20]
	amo, hao	ammonia monooxygenase, hydroxylamine oxidoreductase	[21,22]
	narB, nasA	assimilatory nitrate reductase	[23]
	Nir	assimilatory nitrite reductase	[24]
NH3 assimilation	glnA	glutamine synthetase	[25]
organic N metabolism	ure	urease	[26]