The utilization of Lysinibacillus bacterial powder to induce Fe plaque formation mitigates cadmium and chromium levels in rice

Abstract

The presence of cadmium (Cd) and chromium (Cr) contamination in soil poses an environmental risk to food safety. Microorganisms are crucial for biotransforming heavy metals, but their limited survival in contaminated soils hinders their application in bioremediation. Here, we isolated Lysinibacillus sp. OR-15, which effectively removed Cd(II) and reduced Cr(VI) from the culture. Proteomic analyses and heterologous expression assays showed that QueF, an NADPH-dependent reductase, enhanced bacterial resistance to Cd(II) and Cr(VI), enhancing metal removal capacity. The dry bacterial powder, produced through deep liquid fermentation and spray drying, contained 2.3 × 10¹⁰ viable cells per gram. It effectively reduced Cd and Cr levels in rice grains and maintained a concentration of 10⁵ per gram in soils even after 60 days of cultivation following one application. Scanning and microscopy analysis revealed that Lysinibacillus sp. OR-15 facilitated the formation of iron plaque on rice roots. The formation of iron plaque on the root surface serves as a protective barrier against the upward translocation of heavy metals. Our findings suggest that Lysinibacillus sp. OR-15 exhibits stable and effective properties as a factor for Cd and Cr adsorb on rice iron plaque, thus mitigating the levels of Cd and Cr in rice grains.