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

Abstract

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.