Insights into the molecular mechanism on high salt tolerance of electroactive microorganisms collaborated by biochar supported cerium dioxide

Electroactive microorganisms are a promising approach for treating high-salinity organic wastewater, however, they are highly susceptible to salt stress, which can compromise their metabolic activity. In this paper, biochar supported nano-cerium dioxide catalyst (BC-CeO₂) was prepared to strengthen electroactive microorganisms in high salt environment. It was found that BC-CeO₂ significantly improved the bioelectrochemical and metabolic activity of microorganisms in high salt environment (600 mM NaCl) compared with the Control. At the initial stage of the reaction, the maximum power density of microbial fuel cells (MFCs) reached 343.21 mW/m², and the degradation efficiency of norfloxacin (NOR) was 64.8 %, which was 1.7 times that of the Control. The analysis of microbial antioxidant properties demonstrated that BC-CeO₂ could significantly increase the activities of superoxide dismutase (SOD) and catalase (CAT), effectively enhancing the ability of microorganisms to scavenge reactive oxygen species produced by salt stress. Metagenomic analysis revealed that the abundance of KEGG pathways conducive to microbial growth and metabolism under BC-CeO₂ was relatively high, such as biosynthesis of amino acids (ko01230), microbial metabolism in diverse environments (ko01120) and so on. The enrichment of salt tolerant genes further illustrated the strengthening effect of BC-CeO₂ on microbial adaptation to high salt environment, including genes related to NADH ubiquinone oxidoreductase, Na⁺/H⁺ antiporter, intracellular small molecule compatible substance synthesis and transport related enzyme system and K⁺ transporter related genes. Furthermore, the activity changes of Na⁺/K⁺-ATPase, which regulates cell permeability, in different environments also confirmed this point. This paper provides an effective strategy for enhancing the treatment of high-salt organic wastewater by electroactive microorganisms.