Root-Exuded Metabolites Recruit Selenium-Transforming Microbiota to Enhance Plant Selenium Acquisition

Microbial fortification represents a promising approach for selenium biofortification in crops. Building on the previous discovery that Bacillus cereus SESY enhances selenium uptake in Brassica napus, this study employed an integrated multi-omics approach to investigate the mechanism by which B. cereus SESY enhances Se bioavailability in the Brassica napus rhizosphere. Inoculation with B. cereus SESY significantly increased selenium content in Brassica napus roots and shoots in calcareous soil by 42.9% and 21.5%, respectively, and increased the selenium content of shoots in yellow brown soil by 30.7%. B. cereus SESY promoted the transformation of residual Se into bioavailable forms and enriched bacterial taxa with high motility and Se-transforming capacity (e.g., Lysobacter, Rhodanobacter, Sphingomonas and Burkholderiaceae) in rhizosphere soil. Key genes of these bacteria involved in Se metabolism (e.g., trxA, narH, cysE, cysK, metB) and cell motility genes (e.g., FlgG, CheW, FliH) were up-regulated. Core rhizosphere metabolites such as N-formylmethionine and xanthine correlated strongly with enriched bacteria abundance and available Se. Joint application of these metabolites with enriched bacteria increased plant Se content by 144% and rhizosphere soil available Se by 13.4%. These results reveal a metabolite-mediated microbial network that enhances Se mobility and plant uptake, providing a novel strategy for microbiome-driven biofortification.