Quantitative determination of selenite transformation by Enterobacter sp. YSU and Stenotrophomonas maltophilia OR02

Abstract

The Y-12 plant in Oak Ridge, TN processed uranium and lithium to produce nuclear weapons during World War II and the Cold War. Because the production of nuclear weapons during these time periods was urgent, waste from these processes was not properly contained and nearby East Fork Poplar Creek was contaminated with mercury and other heavy metals. Enterobacter sp. YSU and Stenotrophomonas maltophilia Oak Ridge strain 02 (S. maltophilia 02), which were isolated from East Fork Poplar Creek, are resistant to several heavy metals and selenite, an oxyanion of selenium. The general resistance mechanism appears to be a reduction to elemental selenium. The sodium selenite that is added initially to logarithmically growing culture of these strains is clear in color but turns red when it reaches stationary phase. The change in color could be a result of the reduction of soluble selenite to insoluble elemental selenium. We examined the ability of Enterobacter sp. YSU and S. maltophilia 02 to remove 40 mM selenite and 10 mM selenite, respectively, from their growth. Two cultures were prepared: one was exposed to selenite during early log phase and the control was treated with sterile water. Cells and media were collected at an hourly basis and digested using nitric acid. Then, the amount of selenium in each sample was determined using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Both strains appeared to sequester elemental selenium, but not at high enough levels to significantly decrease the amount of selenite in the growth medium.