Amplification of Nitrogenase nirH Gene Amplicoms The gene that codes for the Fe protein polypeptide of the nitrogenase enzyme is the nifH gene. Thus, the detection of he mind Eene in the genomic A sample of a bacterial isolate would label that particular isolate as a nitrogen fixer. In order to amplify the nifH gene, a nested PCR using outer primers FGPHI(5'-TACGGCALARGGTGG NATHG-3'), PolR(5 ATSGCCATCAT YNTCRCCGGA- 3 and inner primers PolF(5 TGC GAYCCSA ARGCB GAA CTC-3) and AoER(5'-GACGATGTAGATYTCCTG- 3) BII was performed in a Esco S t MaxPro Thermal Cycler. In the first step, a 25 ul PCR mixture consisted of 12 5 Hi Dream Tag Green PCR Master Mix 2x Ther moscientifico. 2 pi Genomic DNA prepared with Zymo Research Fungal/Bacterial DNA MiniPrep 0.5 HM o each primer and 10 pl nuclease-free water ThermoScien tific). The reaction was carried out as follows: initial denaturation at 94 °C for 4 min, 30 cycles at 94 C for 1 min. 55 C for 1 min and 72 5C for 2 mun. and final extension at 72 C for 5 min. In the second step, a 25 pl PCR mixture consisted of 12.5 pl DreamTag Green PCR Master Mix 2 x ThermoScientifico. 2 pl template from the first step, 0.5 M of each primer and 10 pl Nuclease free water. The reaction was camed out as n the first step except the annealing temperature was set to 56 dC instead of 55 oC. A strain of Enterobacie sp. MoP l-1[4] was used as a positive control. The PCR products were sepa rated by electrophoresis in 1.2 agarose gels stained with ethidium bromide Sigma-Aldrich) and visualized under UV lighl.