Abstract: Through the ferrous sulfide gradient tube and phenanthroline spectrophotometric experiments, the ability of Fe(II)oxidation for strain LLDRA6 was explored. By using methods such as scanning electron microscope-energy spectrum analysis (SEM-EDS), dithionite-citrate-bicarbonate (DCB) extraction test, and the measurement of Cd content in two rice varieties, the effect of strain LLDRA6 on the formation of IP and its effect on the migration of Cd from soils to ricewere discussed. The results showed that strain LLDRA6 formed an obvious Fe(II) oxidation circle in the ferrous sulfide gradient tube. In the presence of strain LLDRA6, the Fe(II) oxidation rate of LB liquid medium was higher than that of LB liquid medium without LLDRA6 (the control group), suggesting that this strain was an Fe(II)-oxidizing bacterium(FeOB); SEM-EDS results showed that, after addition of strain LLDRA6 and Fe(II) ions in soils, layered precipitates were formed on the surface of the rice roots, and the energy spectrum analysis (EDS) demonstrated that a large amount of Fe element were contained in these precipitates; the DCB extraction test showed that after treatment with strain LLDRA6 and Fe(II), the Fe content of IP was significantly higher than that of IP formed in other treatment groups, indicating that the strain facilitated the formation of IP. Moreover, the Cd content of the stems, leaves and grains were significantly lower than that of corresponding parts of rice grown in other treatment groups. These results demonstrated that strain LLDRA6 benefited to form IP around rice root surfaces, and the IP had a significant blocking effect on the migration of Cd from soils to rice.

Key words: Fe(II)-oxidizing bacterium, rice, iron plaque, roots, heavy metals, Cd