Bacterial reduction of selenite to elemental selenium

It is well known that many microorganisms can reduce the highly toxic soluble selenium oxyanions (selenate and selenite) to a much less toxic insoluble form, namely elemental selenium. We are developing a bacterial treatment system to mitigate selenium-contaminated waste streams using Pseudomonas fluorescens and Bacillus subtilis, respectively, as model Gram (-) and (+) soil bacteria. Our studies demonstrate that both strains reduce selenite to elemental selenium. The selenite detoxification system is independent of nitrite and sulfite electron accepters, but dependent on the substrate provided for growth. Elemental selenium is deposited as granules throughout the cell, or between the cell wall and the plasma membrane in P. fluorescens and B. subtilis, respectively. In B. subtilis, thioredoxin is induced in the presence of selenite.