Extracellular polysaccharide-facilitated selenium nanoparticle assembly and metabolic reprogramming support efficient...

The environmental accumulation of toxic selenite poses a significant threat to public health and ecosystem sustainability. To improve the capability of microorganisms in selenite detoxification and biotransformation, a superior mutant of Lactiplantibacillus plantarum Vse252 was obtained via ARTP mutagenesis integrated with adaptive evolution. The mutant displayed remarkably enhanced selenite tolerance, with a maximum tolerable concentration reaching 300 mM. Furthermore, it converted 60 % of selenite to elemental selenium in 48 h, showing a remarkable improvement in selenium nanoparticles (SeNPs) biosynthesis. Electron microscopic observations showed that mutant maintained intact cell walls under selenite stress and abundantly produced uniformly dispersed SeNPs. Notably, the mutant produced 216.71 mg/L of extracellular polysaccharide (EPS) under selenite induction, a level markedly higher than that of the WT strain. Proteomic and metabolomic analyses revealed a global metabolic reprogramming in mutant, the upregulation of the pentose phosphate pathway and amino/nucleotide sugar metabolism (RfbA/RfbC) supplied NADPH and precursors for cell wall and EPS synthesis, while elevated oxidoreductases (GshR/Gpo) and cofactors (FMN/FAD) drove efficient selenite reduction. Four key mutated genes, including EmrE, MreC, MoaA, and AcpP, were identified via comparative genomic analysis, further confirming that cell wall homeostasis and transmembrane substance transport play critical regulatory roles in shaping the phenotypic characteristics of the mutant strain. This study reveals a tight association between the biosynthesis of extracellular SeNPs and EPS during microbial resistance to inorganic selenium stress, and highlights their pivotal roles in microbial detoxification, providing mechanistic insights and candidate targets for engineering strains toward selenium bioremediation and functional SeNPs production.