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Applied and Environmental Microbiology, September 2006, p. 6331-6344, Vol. 72, No. 9
0099-2240/06/$08.00+0     doi:10.1128/AEM.00813-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Global Molecular and Morphological Effects of 24-Hour Chromium(VI) Exposure on Shewanella oneidensis MR-1

Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,¹ Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,² Graduate School of Genome Science and Technology, University of Tennessee-Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830,³ Life Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,⁴ Institute for Environmental Genomics and Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019,⁵ Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907⁶

Received 6 April 2006/ Accepted 6 July 2006

The biological impact of 24-h ("chronic") chromium(VI) [Cr(VI) or chromate] exposure on Shewanella oneidensis MR-1 was assessed by analyzing cellular morphology as well as genome-wide differential gene and protein expression profiles. Cells challenged aerobically with an initial chromate concentration of 0.3 mM in complex growth medium were compared to untreated control cells grown in the absence of chromate. At the 24-h time point at which cells were harvested for transcriptome and proteome analyses, no residual Cr(VI) was detected in the culture supernatant, thus suggesting the complete uptake and/or reduction of this metal by cells. In contrast to the untreated control cells, Cr(VI)-exposed cells formed apparently aseptate, nonmotile filaments that tended to aggregate. Transcriptome profiling and mass spectrometry-based proteomic characterization revealed that the principal molecular response to 24-h Cr(VI) exposure was the induction of prophage-related genes and their encoded products as well as a number of functionally undefined hypothetical genes that were located within the integrated phage regions of the MR-1 genome. In addition, genes with annotated functions in DNA metabolism, cell division, biosynthesis and degradation of the murein (peptidoglycan) sacculus, membrane response, and general environmental stress protection were upregulated, while genes encoding chemotaxis, motility, and transport/binding proteins were largely repressed under conditions of 24-h chromate treatment.