Antioxidant CeO2 doped with carbon dots enhance ammonia production by an electroactive Azospirillum humicireducens SgZ-5T

Microbial nitrogen fixation is a fundamental process in the nitrogen cycle, providing a continuous supply of biologically available nitrogen essential for life. In this study, we combined cerium oxide-doped carbon dots (CeO2/CDs) with electroactive nitrogen-fixing bacterium Azospirillum humicireducens SgZ-5T to enhance nitrogen fixation through ammonium production. Our research demonstrates that treatment of SgZ-5T cells with CeO2/CDs (0.2 mg mL−1) resulted in a 265.70% increase in ammonium production compared to SgZ-5T cells alone. CeO2/CDs facilitate electron transfer in the biocatalytic process, thereby enhancing nitrogenase activity. Additionally, CeO2/CDs reduce the concentration of reactive oxygen species in SgZ-5T cells, leading to increased ammonium production. The upregulation of nifD, nifH and nifK gene expression upon incorporation of CeO2/CDs (0.2 mg mL−1) into SgZ-5T cells supports this observation. Our findings not only provide an economical and environmentally friendly approach to enhance biological nitrogen fixation but also hold potential for alleviating nitrogen fertilizer scarcity. In this work, we utilized a hybrid system that incorporates the bio-compatible antioxidant CeO2/CDs and electroactive Azospirillum humicireducens SgZ-5T to give 2.6-fold increased ammonium production compared to that of SgZ-5T cells without treatment. These findings provide a simple strategy for enhancing biological nitrogen fixation and can be applied in other areas of microbial biotechnology. [Display omitted] •Antioxidant CeO2/CDs are prepared to be incorporated with A. humicireducens SgZ-5T.•The above hybrid shows a 2.6-fold increased NH4+ production compared to cells only.•CeO2/CDs enhance nitrogenase activity and decrease ROS concentrations in SgZ-5T.•Treatment by CeO2/CDs induces the up-regulated expression of nifD, nifH and nifK.