Cadmium-resistant rhizobacterium Bacillus cereus M4 promotes the growth and reduces cadmium accumulation in rice (Oryza sativa L.)

Rice farmland cadmium pollution is an increasing problem for food safety. Cd-resistant bacterial strain was isolated from rice rhizosphere soil and identified as Bacillus cereus M4. Treatment with M4 fermentation broth increased rice seedlings growth in vermiculite, while reduced Cd accumulation in grains of rice grown in Cd-contaminated potted soil from 0.309 to 0.186 mg/kg. Indoleacetic acid (IAA) was detected in M4 metabolites and in potted soil solutions supplemented with M4 broth. M4 broth increased the abundance of Bacillus from 0.54% to 0.95% and changed the soil bacterial community composition. These findings indicate that M4 promotes rice growth by secreting IAA and altering the rhizospheric soil microenvironment, via soil solution composition and microbial community, which may affect Cd translocation from soil to rice roots, thereby decreasing grain Cd accumulation. Therefore, B. cereus M4 is potentially suitable for the bioremediation of Cd-contaminated paddy soils.