Fate of selenate and selenite metabolized by Rhodobacter sphaeroides

Cultures of a purple nonsulfur bacterium, Rhodobacter sphaeroides, amended with similar to1 or similar to 100 ppm selenate or selenite, were grown phototrophically to stationary phase. Analyses of culture headspace, separated cells, and filtered culture supernatant were carried out using gas chromatography, X-ray absorption spectroscopy, and inductively coupled plasma spectroscopy-mass spectrometry, respectively. While selenium-amended cultures showed much higher amounts of SeO32- bioconversion than did analogous selenate experiments (94% uptake for SeO32- as compared to 9.6% for SeO32--amended cultures from 100-ppm solutions), the chemical forms of selenium in the microbial cells were not very different except at exposure to high concentrations of selenite. Volatilization accounted for only a very small portion of the accumulated selenium; most was present in organic forms and the red elemental form.