• One biofilm-overproducing mutant Bacillus subtilis strain B12 were constructed. • B12 induced lower Cd availability and uptake in edible tissue of Chinese cabbage. • B12 induced higher polysaccharide content and invertase activity in soil. • B12 induced higher Cd-adsorption related cumA, epsA , and cadA gene copies in soil. • B12 showed higher colonization and biofilm formation on the vegetable root surface. Biofilm-producing bacteria can decrease Cd uptake in vegetables, but mechanisms underlying this effect are poorly characterized. In this study, two mutant strains B12Δ Ywcc and B12Δ SlrR were constructed from a biofilm-producing Bacillus subtilis strain B12. Then, the impacts of strain B12 and its high biofilm-producing mutant strain B12Δ Ywcc and low biofilm-producing mutant strain B12Δ SlrR on Cd availability and uptake in Chinese cabbage and the related mechanisms were investigated in the Cd-polluted soil. Strain B12 and its mutants B12Δ Ywcc and B12Δ SlrR increased the dry biomasses of edible tissues by 54%–130% compared with the controls. Strain B12 and its mutant B12Δ Ywcc reduced the soil available Cd content by 36%–50% and root and edible tissue Cd contents by 23%–50% compared with the controls. Furthermore, the mutant strain B12Δ Ywcc reduced the edible tissue Cd content by 40% and increased the polysaccharide content by 23%, invertase activity by 139%, and gene copies of the cumA by 4.5-fold, epsA by 7.1-fold, and cadA by 4.3-fold, which were involved in Cd adsorption in the rhizosphere soils, respectively, compared with strain B12. The polysaccharide content and cumA, epsA , and cadA gene copy numbers showed significantly reverse correlations with the available Cd content. Notably, the mutant strain B12Δ Ywcc showed better ability to colonize the vegetable root surface than strain B12. These findings demonstrated that the biofilm-overproducing mutant strain B12Δ Ywcc increased the polysaccharide production and Cd-immobilizing related cumA, epsA , and cadA gene copies, resulting in lower Cd availability and accumulation in Chinese cabbage in the Cd-polluted soil. [ABSTRACT FROM AUTHOR]