Selenium Biofortification Potential of Bacillus cereus: Foliar Inoculation Promotes the Absorption of Exogenous Organic Se in Pak Choi

Selenium (Se) is an essential trace element for human health, and dietary intake serves as a primary route for Se supplementation. Biofortification, as an ecological and efficient agricultural biotechnology, holds significant potential for producing Se-enriched agricultural products. This study investigated the effect and mechanism of Bacillus cereus (Y2) in enhancing the absorption of selenomethionine (SeMet) in pak choi (Brassica rapa subsp. chinensis) via foliar application. Through pot experiments combined with in vitro absorption kinetics, physiological measurements, and transcriptomic analysis, the plant growth-promoting and Se-enrichment functions of this strain were systematically evaluated. The results indicated that Bacillus cereus Frankland & Frankland, 1887 (Bacteria, Bacillaceae) could stably colonize pak choi leaves, significantly increasing plant biomass, leaf area, and photosynthetic parameters. Selenium absorption kinetic analysis revealed that inoculation significantly enhanced the absorption rate of SeMet by pak choi. Under conditions of 20 mg/L SeMet, inoculation increased the Se content in shoots and roots by 32.6% and 42.8%, respectively, and Se accumulation was also significantly elevated. Transcriptomic analysis further revealed that pathways related to photosynthesis, plant hormone signal transduction, and aquaporin synthesis were significantly enriched in pak choi leaves following B. cereus inoculation, with upregulation of key genes including LHCB2, BrPIP2, IAA, and AHP. This study elucidates that B. cereus synergistically promotes plant Se absorption through multi-dimensional physiological and molecular pathways, providing a new theoretical basis and technical reference for developing foliar microbial inoculants to achieve Se biofortification in crops.