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Appl. Environ. Microbiol., Aug 1997, 3079-3084, Vol 63, No. 8
ME Losi and WT Frankenberger Jr
A facultative bacterium capable of removing the selenium (Se) oxyanions
selenate (SeO(inf4)(sup2-)) and selenite (SeO(inf3)(sup2-)) from solution
culture in flasks open to the atmosphere was isolated and studied with the
goal of assessing its potential for use in bioremediation of seleniferous
agricultural drainage water. Elemental Se (Se(sup0)) was confirmed as a
product of the reaction. The organism, identified as Enterobacter cloacae
and designated strain SLD1a-1 (ATCC 700258), removed from 61.5 to 94.5% of
added SeO(inf4)(sup2-) (the primary species present in agricultural
drainage water) at concentrations from 13 to 1,266 (mu)M. Equimolar amounts
of nitrate (NO(inf3)(sup-)), which interferes with SeO(inf4)(sup2-)
reduction in some organisms, did not influence the reaction in growth
experiments but had a slight inhibitory effect in a washed-cell suspension.
Washed-cell suspension experiments also showed that (i) SeO(inf3)(sup2-) is
a transitory intermediate in reduction of SeO(inf4)(sup2-), being produced
and rapidly reduced concomitantly; (ii) NO(inf3)(sup-) is also reduced
concomitantly and at a much higher rate than SeO(inf4)(sup2-); and (iii)
although enzymatic, reduction of either oxyanion does not appear to be an
inducible process. Transmission electron microscopy revealed that
precipitate particles are <0.1 (mu)m in diameter, and these particles
were observed free in the medium. Evidence indicates that SLD1a-1 uses
SeO(inf4)(sup2-) as an alternate electron acceptor and that the reaction
occurs via a membrane-associated reductase(s) followed by rapid expulsion
of the Se particles.
Copyright © 1997, American Society for Microbiology
Reduction of Selenium Oxyanions by Enterobacter cloacae SLD1a-1: Isolation and Growth of the Bacterium and Its Expulsion of Selenium Particles
Department of Soil and Environmental Sciences, University of California, Riverside, California 92521
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