Isolation of a Pseudomonas nitrate-reducing bacterium and study of its influence by Fe(II)

Using the plate streak isolation method, a nitrate-reducing bacterium named ZX was isolated from the anaerobic layer of river sediments. Through morphological observation, this bacterium was found to be in a short rod shape, with white circular colonies and smooth edges. The 16S rRNA gene sequencing analysis identified it as a Pseudomonas sp. The whole genome sequencing and functional gene annotation revealed that strain ZX carried a complete denitrification gene cluster (nar, nir, nor, nos), possessing potential denitrification functions. To investigate the nitrate reduction-coupled ferrous oxidation metabolic activity of strain ZX, sodium nitrate was used as the electron acceptor, and different concentrations of Fe(II) (1, 3, 5 mM) and sodium acetate were used as the electron donors for the culture experiment. The results showed that strain ZX could oxidize ferrous through the chemical denitrification pathway under higher Fe(II) concentrations, and the Fe(II) concentration had a regulatory effect on the bacterial metabolic activity. 1 mM Fe(II) significantly promoted bacterial growth and metabolism, while at 5 mM Fe(II) condition, the bacterial metabolism was inhibited in the early stage and gradually recovered and completed oxidation, indicating that the strain had certain adaptability to higher concentrations of ferrous. All treatment groups detected nitrite accumulation, showing the characteristics of incomplete denitrification, suggesting that the nitrite reductase of the strain might be inhibited.