Purification of Selenium-Contaminated Soils Using the Selenate Reducing Bacterium Stutzerimonas stutzeri NT-I

Selenium (Se) is a rare metal found mainly in volcanic sediments. As Japan has many sulfide deposits, selenium is naturally widely distributed at low concentrations. Selenium exists in soil as soluble seleno-oxyanions, such as selenate [Se (VI)] and selenite [Se (IV)], which are highly toxic. The Japanese government has standards for soluble selenium concentrations in soil that can be achieved by water shielding or the addition of insolubilization agents. However, as these treatments leave selenium in the soil, it cannot be reused because of a risk of selenium re-elution. To solve this problem, we attempted to rapidly insolubilize soluble seleno-oxyanions in the soil by adding a bacterium, Stutzerimonas stutzeri NT-I, which reduces selenate [Se (VI)] through selenite [Se (IV)] to insoluble elemental selenium [Se (0)] and then elemental selenium to volatile dimethyl diselenide (DMDSe). We attempted purification of selenate-contaminated soil using S. stutzeri NT-I. Under optimal culture conditions, 46% of the initial selenate concentration was removed from the selenate-contaminated soil reducing Se elution below the designated standards within 72 h. These results indicate that bioremediation using S. stutzeri NT-I is effective for selenate-contaminated soil.