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ABSTRACT
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.
DOI: 10.1128/AEM.00813-06
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