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
Abstract
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.