Arsenic contamination threatens rice (Oryza sativa) production, yet the synergistic use of iron plaque (IP) and root-associated biofilms as a rhizosphere barrier to limit arsenic uptake remains unexplored. To address this, we engineered an arsenic-resistant (AR) plant growth-promoting rhizobacterium (AR-PGPR), Bacillus subtilis p43-Taglo1, expressing the speciation-inert arsenic-binding protein TaGlo1. In a contaminated paddy, this strain increased grain yield by 10.7-11.6% and reduced grain arsenic by 28.2-37.4% compared to the wild-type. The engineered strain robustly colonized roots and enhanced the formation of a functional IP-biofilm composite, which sequestered more arsenic. This was driven by a 2.87-fold increase in Fe(II) oxidation and elevated production of extracellular polymeric substances (EPS) (1.4-fold) and siderophores (1.5-fold). Transcriptomic analysis revealed that inoculation upregulated bacterial genes for Fe(II) oxidation, siderophore, and EPS biosynthesis, while in rice roots, it activated phytohormone pathways and downregulated arsenite transporters (OsLsi1 and OsLsi2). We conclude that AR-PGPR can restore beneficial root-microbe interactions under arsenic stress. The IP-biofilm composite acts as an inducible barrier essential for the dual benefits of arsenic exclusion and growth promotion. Our study shows that AR rhizobacteria fortify the IP-biofilm composite to reduce arsenic uptake and promote rice growth, providing a route toward safer rice production in arsenic-affected regions.
Li et al. (Wed,) studied this question.