Molecular Screening of Nitrate Reductase Enzyme in Native Halophilic Bacteria of Iran

With the increased usage of nitrate fertilizers, the removal of their stable ionic and water-soluble end products is a challenge for human health. Several physicochemical methods have been examined for nitrate removal of water, but biological treatments are mostly preferred due to a higher efficiency and lower cost. To remove nitrogen from water, we investigated the potential of nitrate-reducing halophilic and halotolerant bacteria. A total of 50 strains from different saline and hypersaline environments of Iran, including the Incheboron wetland, Aran-Bidgol salt-lake, and Urmia endorheic salt-lake, were screened for nitrate reductase production. Among investigated bacteria, 60% and 19% of strains obtained from Urmia lake, and Incheboron wetland produced nitrate reductases, respectively. The nitrate reductase coding genes narG, and napA were analyzed in all strains with confirmed nitrate-reducing capacity. The napA gene was successfully amplified from a gram-negative halophilic strain, and the narG gene was detected in ten halophilic strains. Among nitrate-reducing isolates with the narG gene expression, the Kocuria rosea strain R3A34 showed the highest nitrate reductase production level. This strain was selected to optimize for its denitrifying activity. Results showed that 32°C, pH 7.0, NaCl 8% (w/v), and mannitol (as a carbon source) provide the optimal environmental conditions for the efficient production of nitrate reductase by the Kocuria rosea strain R3A34. As these are compatible with wastewaters conditions, this bacterium can be a proper candidate for bioremediation of wastewaters from nitrate pollutants.