Nitrous oxide, which is produced as an intermediate of denitrification, has a noteworthy global warming potential by absorbing infrared radiation. During the denitrification process, nitrate is reduced by nitrate reductases, nitrite reductases, nitric oxide reductases and nitrous oxide reductases, which are encoded by the napA gene or the narG, nirS or nirK, nor and nosZ genes respectively. A variety of samples have been studied using the nirK, nirS and nosZ genes as molecular markers to indicate the diversity and abundance of denitrifiers in various environments.