Lactiplantibacillus plantarum S1 as a Novel Dual-Functional Probiotic Strain for High-Efficiency Organoselenium Biotransformation in Functional Food Development

The microbial conversion of inorganic Se into bioactive organoselenium compounds represents a cutting-edge strategy for developing functional foods with enhanced nutritional value. This study introduces Lactiplantibacillus plantarum S1, a novel Se-enriched probiotic strain isolated from traditional Chinese sauerkraut, and systematically optimizes its capacity for selenite biotransformation. Critical fermentation parameters—including sodium selenite supplementation timing (2 μg/mL added at mid-log phase, 7 h post-inoculation), pH (5.0), and anaerobic cultivation duration (12 h)—were identified as key determinants of conversion efficiency. The optimized protocol achieved a 72.3% organoselenium conversion yield, producing 626.6 μg/g cellular organoselenium while maintaining probiotic viability (2.28 × 10 9 CFU/mL). Se speciation analysis demonstrated that 78.51% of intracellular Se existed in organic forms, with protein-bound Se constituting the predominant fraction (85.33%), followed by polysaccharide-associated (6.42%) and nucleic acid-linked (3.38%) species. The strain’s dual functionality as both an efficient Se bioconverter and a resilient probiotic carrier highlights its potential for nutraceutical applications. These findings not only establish a robust bioprocess for Se-enriched probiotic production but also reveal mechanistic insights into preferential Se incorporation into protein matrices. This work bridges microbial Se metabolism research with scalable functional food innovation, offering a sustainable platform for developing Se-fortified products with dual health benefits.