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Applied and Environmental Microbiology, January 2004, p. 52-60, Vol. 70, No. 1
0099-2240/04/$08.00+0 DOI: 10.1128/AEM.70.1.52-60.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Jodi Switzer Blum,1 Sean Langley,2 Terry J. Beveridge,2 Pulickel M. Ajayan,3 Thomas Sutto,4 Amanda V. Ellis,5 and Seamus Curran5
Water Resources Division, U.S. Geological Survey, Menlo Park, California 94025,1 Department of Microbiology, College of Biological Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1,2 Department of Materials Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180,3 Chemistry Division, Naval Surface Warfare Center, Dahlgren, Virginia 22448,4 Physics Department, New Mexico State University, Las Cruces, New Mexico 880015
Received 29 July 2003/ Accepted 8 October 2003
Certain anaerobic bacteria respire toxic selenium oxyanions and in doing so produce extracellular accumulations of elemental selenium [Se(0)]. We examined three physiologically and phylogenetically diverse species of selenate- and selenite-respiring bacteria, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter shriftii, for the occurrence of this phenomenon. When grown with selenium oxyanions as the electron acceptor, all of these organisms formed extracellular granules consisting of stable, uniform nanospheres (diameter,
300 nm) of Se(0) having monoclinic crystalline structures. Intracellular packets of Se(0) were also noted. The number of intracellular Se(0) packets could be reduced by first growing cells with nitrate as the electron acceptor and then adding selenite ions to washed suspensions of the nitrate-grown cells. This resulted in the formation of primarily extracellular Se nanospheres. After harvesting and cleansing of cellular debris, we observed large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species. The spectral properties in turn differed substantially from those of amorphous Se(0) formed by chemical oxidation of H2Se and of black, vitreous Se(0) formed chemically by reduction of selenite with ascorbate. The microbial synthesis of Se(0) nanospheres results in unique, complex, compacted nanostructural arrangements of Se atoms. These arrangements probably reflect a diversity of enzymes involved in the dissimilatory reduction that are subtly different in different microbes. Remarkably, these conditions cannot be achieved by current methods of chemical synthesis.
Present address: Department of Geology & Earth Sciences, Stanford University, Stanford, CA 94305.
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