Cobalt ferrite nanozyme for efficient symbiotic nitrogen fixation via regulating reactive oxygen metabolism

Abstract

Biological nitrogen fixation is essential to crop production, but it can be inhibited by high concentrations of reactive oxygen species (ROS) due to the irreversible inactivation of the nitrogenase complex, thus posing a threat to food security and sustainable agricultural development. Here, we constructed an antioxidant cobalt ferrite (CoFe₂O₄) nanozyme as a bridge between nanotechnology and biological nitrogen fixation, which was shown to efficiently regulate the reactive oxygen metabolism and protect nitrogenase, thereby significantly enhancing the symbiotic nitrogen fixation efficiency by 260% in Glycine max (L.) Merr. (soybean). The CoFe₂O₄ nanozyme was also revealed to effectively reduce the concentration of ROS in the nodule by 56.6%, creating a superior environment for the proliferation of rhizobia and forming more effective nodules (larger nodules for an increase of 45.6% in the number of parasitic rhizobia). Furthermore, the CoFe₂O₄ nanozyme was shown to act as a synergist of leghemoglobin and increase its accumulation by 45.9%, where the high concentration of leghemoglobin in nodular cells can create a relatively hypoxic environment and protect nitrogenase, thus achieving a quantitative leap in nitrogen fixation capacity and simultaneously increasing the soybean photosynthesis by 67.2%. Our study has demonstrated that the CoFe₂O₄ nanozyme can efficiently regulate the intracellular ROS metabolism and serve as a promising strategy for enhancing symbiotic nitrogen fixation.