Promoting denitrification via high electron conversion ratio in the iron valence Cycle: Prospects for Pseudomonas sp. JM-7 application in environmental engineering

Abstract

The interdependence between iron and nitrogen in the environment is of utmost importance, and this study has explored the intricate relationship between denitrification and iron valence cycling using Pseudomonas sp. strain JM-7 (P. JM-7) as a model bacteria. Our research demonstrated that P. JM-7 had the ability to effectuate electron transfer from the periplasmic space to electron acceptors, such as nitrate, via Cytochrome c-proteins (c-Cyts). We found that iron valence state transformations with Fe(II)/Fe(III) promoted P. JM-7′s denitrification of nitrate coupled to yeast extract powder (YEP) oxidation. Denitrification rates depended on temperature (>21 °C) and pH (6–9). During logarithmic growth, 5 g/L YEP enabled 350 mg/L nitrate removal, increasing to 1650 mg/L in stable growth. Addition of 4 mM Fe(II)/Fe(III) increased denitrification to 500 mg/L during logarithmic growth. The dynamic test results displayed that compared to the SiO2 filler control group, iron-containing fillers could facilitate P. JM-7 to reduce 100 mg/L nitrate with 50 mg/L YEP electrons, corresponding to 6 times the maximum electron transfer efficiency in the static test. Overall, iron redox cycling significantly enhanced P. JM-7 denitrification, imparting insights into iron–nitrogen interactions. In summary, our research imparts valuable insights into the nexus between iron and nitrogen in the environment, highlighting the potential application of P. JM-7 in environmental engineering. Our findings indicate that P. JM-7 exhibits a significant denitrification capability, and further research is recommended to investigate its ability to remove phosphorus and promote sustainable environmental remediation practices.