Denitrification is a part of the nitrogen cycle that is performed nearly exclusively by bacteria. During denitrification, a series of N-oxide reductases catalyze the reduction of nitrate to dinitrogen gas. One of the intermediates in this process is nitric oxide (NO) which is a freely diffusible toxic gas. Whether or not the NO produced during denitrification causes significant damage to the cell depends on the amount of NO that is produced and the ability of the bacterial cell to cope with NO-mediated damage.