Jiang, Wenbiao, Delineating the Distribution of Selenium in Bacterial Cultures That Reduce and Methylate Oxyanions of This Toxic Metalloid. Master of Science (Chemistry), December, 1993, Sam Houston State University, Huntsville, Texas. 48 pp. (pdf version of this thesis)

This research was undertaken for the purpose of developing a method and using this method to analyze the distribution of selenium species in bacterial cultures which reduce and methylate oxyanions of this toxic metalloid.
The analytical methods developed were based on atomic absorption spectroscopy for selenium at 196.0 nm and colorimetric method for selenium using 3,3'-diaminobezedine reagent. Pseudomonas fluorescens K27 bacteria was used for this research and tryptic soy broth containing 0.1% potassium nitrate was used for growth of the bacteria. Selenite, selenate and elemental selenium amended bacterial cultures grown in aerobic and anaerobic conditions were analyzed in this work.
The analytical procedures developed for selenium delineation were found useful in this research: the results of spike addition method show the suitability of the adopted wet ashing procedure using nitric acid for the biological precipitate and elemental Se; the matrix effect investigation using standard addition and serial dilution methods indicated that the matrix effect of these biological samples were not significant to the atomic absorption spectroscopy for Se analysis. The spectrophotometric measurement of selenite by 3,3'-diaminobezedine reagent after quantitative reduction of selenate to selenite could be used to differentiate the selenite and selenate in the bacterial cultures. The comparison between atomic absorption spectroscopy and colorimetric method for Se confirmed this analytical procedure was suitable for this research.

The selenium distribution of the bacterial culture analyzed by this pathway indicated that the only cultures that were found to produce volatile Se and elemental Se in our experiments contained live aerobic or anaerobic bacteria. Selenite amended cultures grown either aerobically and anaerobically produced more elemental Se than similar selenate amended cultures. Selenate poisoned cultures grown either aerobically and anaerobically produced more volatile Se than similar selenite poisoned cultures.

Finally, selenite was oxidized to selenate by atmospheric oxygen in sterile tryptic soy broth media containing 0.1% potassium nitrate treated aerobically, though the amount is relatively small.

Thomas G. Chasteen
Thesis Director

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