Biogenic Selenium Nanoparticles from Food-Grade Pediococcus acidilactici JD-21: Selenite Bioreduction, Enhanced Probiotic Traits, and Antioxidant Protection

Selenite bioreduction by food-grade lactic acid bacteria enables mild production of selenium nanoparticles (SeNPs) together with selenium-enriched biomass. Here, a highly Se(IV)-tolerant isolate from Enshi soil was identified as Pediococcus acidilactici JD-21, which efficiently reduced 5 mmol/L Se(IV) and accumulated SeNPs with an average diameter of 46.4 ± 7.7 nm, potentially associated with protein- and polysaccharide-related biomolecules. Selenium enrichment markedly enhanced the antibacterial activity of JD-21 against Escherichia coli, Staphylococcus aureus and Salmonella enteritidis and improved survival in simulated gastric juice, indicating probiotic potential. In a mouse Streptococcus suis infection model, oral-gavage SeNPs alleviated infection-associated weight loss, restored antioxidant enzyme activities and reduced liver and spleen lesions. RNA-seq revealed 537 Se(IV)-responsive genes, with up-regulated redox, lipid/exopolysaccharide and transport pathways and down-regulated growth-related functions. These findings demonstrate that JD-21 is a promising food-grade chassis for producing biogenic SeNPs and selenium-enriched probiotics for selenium fortification and foodborne pathogen control.