| Summary: | Many organisms have been isolated that transform inorganic arsenic compounds
to organoarsenic species. In the case of antimony, simple alkylantimony species have
been detected in the environment, but only a few organisms are known that produce these
species. The fungus Scopulariopsis brevicaulis was selected as a model microorganism to
study antimony biomethylation, because it is known for its ability to biomethylate the
chemically similar element, arsenic.
Cultures of S. brevicaulis were incubated with inorganic antimony compounds.
Volatile antimony biomethylation products, in headspace gases, were determined by
using gas chromatography inductively coupled plasma mass spectrometry, and
nonvolatile species, in media samples, were determined by using hydride generation gas
chromatography atomic absorption spectroscopy. Potassium antimony tartrate and
antimony trioxide were biomethylated. The major biomethylation products (~95%) were
nonvolatile dimethylantimony and trimethylantimony species, found in the medium.
Volatile trimethylstibine (Me3Sb) was produced as a minor biomethylation product
(~5%).
The methyl source for antimony biomethylation was investigated, by incubating
S. brevicaulis with potassium antimony tartrate and CD3-D-methionine, or
13CD3-L-methionine. There was significant, and comparable, incorporation of the methyl
group from L-methionine into alkylantimony and alkylarsenic species. There was
incorporation of the methyl group from D-methionine into alkylarsenic and
alkylantimony species, but less than for L-methionine. These results suggest that
antimony biomethylation proceeds via a mechanism very similar to that of arsenic
biomethylation.
Mixtures of antimony and arsenic compounds were incubated with S. brevicaulis
and the biomethylation products determined. In these interaction studies, it was found
that inorganic antimony(III) compounds inhibited arsenic biomethylation whereas
inorganic arsenic(III) compounds enhanced antimony biomethylation.
Microorganisms, resistant to the germicide, 10, 10'-oxybisphenoxarsine (OBPA),
were isolated. The OBPA-resistant microorganisms, and S. brevicaulis, were incubated
with OBPA for one month and the medium analyzed. There was no evidence, in the form
of OBPA break-down products or intermediates on the pathway to trimethylarsine, to
suggest that any of these microorganisms might produce volatile arsines from OBPA.
Furthermore, when headspace gases from S. brevicaulis cultures, grown in medium
containing OBPA, were analyzed, no significant amounts of trimethylarsine were
detected.
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