Measurement of selenite reduction to elemental selenium by Stenotrophomonas maltophilia OR02

Abstract

Selenium is required by all organisms, but too much can be toxic. Environments that are contaminated with selenium contain large amounts of the oxyanions, selenite and selenate, which are toxic to living organisms. Stenotrophomonas maltophilia OR02 (S. maltophilia 02), which was isolated from a heavy metal contaminated site in Oak Ridge, TN, appears to reduce a clear solution of selenite to non-toxic red elemental selenium when grown in the presence of selenite. To test the ability of this strain to remove selenite from its environment, S. maltophilia02 was grown to early log phase and then exposed to 1 mM selenite. Two control experiments containing 1) cells and growth medium and 2) growth medium and selenite were performed simultaneously. Growth over time was monitored by measuring turbidity in Klett units and viable cell counts. Selenium content in the growth medium and cells was monitored using Inductively Coupled Plasma (ICP) spectroscopy. Selenite affected the log phase of the cell growth, and the mechanism of resistance appeared to be reduction of selenite to elemental selenium. The concentration of selenium decreased in the growth medium and increased in pelleted cells. This reduction process can be a useful tool in bioremediation of selenite in the environment. From our results, when treated with 1 mM of sodium selenite the strain removed 17 % of the selenite.