Using Fluorine-Induced Chemiluminescence To Detect Organo-Metalloids in the Headspace of Phototrophic Bacterial Cultures Amended with Selenium and Tellurium

Verena Van Fleet-Stalder and Thomas G. Chasteen
Department of Chemistry and
Texas Regional Institute for Environmental Studies
Sam Houston State University, Huntsville,Texas, USA



Purple nonsulfur bacteria are resistant to metalloid oxyanions. The key to this resistance seems to lie in the ability of these organisms to reduce and, in some cases, methylate these toxic chemical species. Reduced methylated metalloids are volatile and in this work were specifically and very sensitively analyzed by fluorine-induced chemiluminescence detection after separation by capillary gas chromatography. Six strains of purple nonsulfur bacteria were grown under photo-heterotrophic conditions and exposed to varied concentrations of selenite, selenate, and dimethyl selenone--a proposed intermediate of the selenium oxyanion reduction /methylation pathway. Selenium and tellurium metallic powders were also added to live cultures.

All of the phototrophic bacteria studied here reduced and methylated one or the other oxyanions of Se used and three strains reduced and methylated elemental Te and elemental Se. All strains responded to the addition of dimethyl selenone by producing dimethyl selenide and, in 3 of the 6 strains examined, dimethyl diselenide was also detected. In all six cases the highest amounts of volatile selenium compounds were found in cultures amended with dimethyl selenone and the lowest amounts in cultures doped with selenate.

Some of the phototrophic bacteria studied here, when amended with oxyanions of both Se and Te increased their release of dimethyl telluride--produced by their bioreduction and methylation of tellurate--in the presence of selenate. Control experiments showed that this synergism was biological and not merely caused by the presence of other organo-sulfides or -selenides in culture.