Reduction of selenium oxyanions by Enterobacter cloacae SLD1a-1: isolation and growth of the bacterium and its expulsion of selenium particles

• Published in: Applied and Environmental Microbiology 1997-08, Vol.63 (8), p.3079-3084
• Main Authors: Losi, M.E. (University of California, Riverside, CA.), Frankenberger, W.T. Jr
• Format: Article
• Language: English
• Subjects: ANION; ANIONES; ANIONS; Bacteria; Biological and medical sciences; Biology of microorganisms of confirmed or potential industrial interest; Biotechnology; Cells; ENTEROBACTER; Fundamental and applied biological sciences. Psychology; Microbiology; Mission oriented research; Physiology and metabolism; REDUCCION; REDUCTION; SELENIO; SELENIUM
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.63.8.3079-3084.1997

A facultative bacterium capable of removing the selenium (Se) oxyanions selenate (SeO4(2-)) and selenite (SeO3(2-)) from solution culture in flasks open 10 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(0)) 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 SeO4(2-) (the primary species present in agricultural drainage water) at concentrations from 13 to 1,266 micromolar. Equimolar amounts of nitrate (NO3-), which interferes with SeO4(2-) reduction in some organisms, did not influence the reaction in growth experiments but had a slight inhibitory elect in a washed-cell suspension. Washed-cell suspension experiments also showed that (i) SeO3(2-) is a transitory intermediate in reduction of SeO4(2-), being produced and rapidly reduced concomitantly; (ii) NO3- is also reduced concomitantly and at a much higher rate than SeO4(2-); 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 micrometer in diameter, and these particles were observed free in the medium. Evidence indicates that SLD1a-1 uses SeO4(2-) as an alternate electron acceptor and that the reaction occurs via a membrane-associated reductase(s) followed by rapid expulsion of the Se particles