Evidences of non-reactive mercury-selenium compounds generated from cultures of Pseudomonas fluorescens

This work was designed to determine chemically inert mercury-selenium (Hg-Se) compounds formed in a culture of Pseudomonas fluorescens exposed to Hg(2+) and Se(IV) (selenite). To isolate these compounds, different digestion methods were studied and sodium dodecyl sulfate (SDS) lysis was selected. The Hg(0) and non-reactive Hg were determined in two series of cultures containing 0.0-6.00 μg L(-1) Se(IV) (0.0-76.0 μmol L(-1)) in combination with low 5.00 μg L(-1) (0.025 μmol L(-1)) or high 100 μg L(-1) (0.500 μmol L(-1)) Hg(2+). It was found that Hg(0) formed in the culture decreased with the increase of initial Se(IV), while the non-reactive Hg increased with the Se(IV). In cultures with low initial [Hg(2+)], a median Se(IV) (2.0 μg L(-1) or 25.3 μmol L(-1)) resulted in about 70% of the added Hg(2+) sequestered as non-reactive Hg, and in culture with high initial Hg(2+), about 40% was sequestered. P. fluorescens was proved to be indispensible for the formation of the non-reactive Hg-Se compounds. The Hg:Se molar ratio in the non-reactive Hg-Se compounds was close to 1, suggesting the existence of mercuric selenide in cells. Mechanisms for the formation of the non-reactive Hg-Se compounds are proposed.