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 Hg2+ and SeIV (selenite). To isolate these compounds, different digestion methods were studied and sodium dodecyl sulfate (SDS) lysis was selected. The Hg0 and non-reactive Hg were determined in two series of cultures containing 0.0–6.00 μg L−1 SeIV (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) Hg2+. It was found that Hg0 formed in the culture decreased with the increase of initial SeIV, while the non-reactive Hg increased with the SeIV. In cultures with low initial [Hg2+], a median SeIV (2.0 μg L−1 or 25.3 μmol L−1) resulted in about 70% of the added Hg2+ sequestered as non-reactive Hg, and in culture with high initial Hg2+, 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.

Research Highlights
► P. fluorescens exposed to environmental levels of Hg2+ and selenite can produce solid Hg-Se compounds.
► A procedure was developed to isolate formed solids from the cultures.
► A Hg:Se molar ratio close to 1 of the isolated solids suggests the existence of mercuric selenide.
► Mechanisms of formation of HgSe are suggested.