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 pho totrophically to stationary phase. Analyses of culture headspace, separated cells, and filtered culture supernatant were carried out using gas chromat ography, X-ray absorption spectroscopy, and inductively coupled plasma spec troscopy-mass spectrometry, respectively. While selenium-amended cultures s howed much higher amounts of SeO32- bioconversion than did analogous selena te experiments (94% uptake for SeO32- as compared to 9.6% for SeO32--amende d cultures from 100-ppm solutions), the chemical forms of selenium in the m icrobial cells were not very different except at exposure to high concentra tions of selenite. Volatilization accounted for only a very small portion o f the accumulated selenium; most was present in organic forms and the red e lemental form.