Objective To screen Bacillus altitudinis YC11 from tobacco endophytic bacteria for its high capacity to reduce sodium selenite (Na₂SeO₃), and to elucidate the molecular mechanism of its synthesis of selenium nanoparticles (SeNPs) using multi-omics integrative analysis.

Method Strains with high reducing activity were screened using high-concentration exogenous sodium selenite medium, and the conversion rate of Na₂SeO₃ was determined by atomic fluorescence spectrometry. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and fourier transform infrared spectroscopy (FTIR) were employed to observe the process of SeNPs synthesis by strain YC11 and to characterize the purified SeNPs.The mechanism of green synthesis of SeNPs by strain YC11 was revealed through integrated transcriptomic and proteomic analyses.

Result Bacillus altitudinis YC11 tolerated up to 100 mmol/L Na₂SeO₃, and the conversion rates for 1mmol/L, 3 mmol/L, and 5 mmol/L Na₂SeO₃ reached 95%, 70%, and 45%, respectively, after 48 hours.SEM, EDS, TEM, particle size distribution and ZETA potential analyses revealed that spherical SeNPs were intracellularly synthesized by YC11. The obtained SeNPs exhibited hydrodynamic diameters ranging from 50-500 nm with an average size of 227.08 nm and an apparent zeta potential of −31.4 mV, and these SeNPs were subsequently released extracellularly via rupture of the cell membrane edge.FTIR analysis indicated that the surface of SeNPs was coated with biomacromolecules such as proteins, lipids, and carbohydrates.Integrative transcriptomic and proteomic analyses identify a total of 159 genes/proteins that are significantly differentially expressed at both transcriptional and translational levels in strain YC11 treated with 5 mmol/L sodium selenite relative to the untreated control without sodium selenite supplementation. GO and KEGG enrichment analyses reveal prominent differential expression of genes and proteins involved in selenium compound metabolism, pyruvate metabolism, alanine, aspartate and glutamate metabolism, sulfur transport system, glycolysis/gluconeogenesis energy metabolism, and ABC transporter pathways, which suggests that the sodium selenite reduction process in YC11 is modulated by reductase-related genes gabD, putC, arsC and trxB.

Conclusion Bacillus altitudinis YC11, an endophytic strain from tobacco, is highly tolerant to Na₂SeO₃. This work provides a novel strain resource and a theoretical basis for the development and application of microbially green-synthesized selenium nanoparticles.