Article

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, TN 37831, USA.
Applied and Environmental Microbiology (Impact Factor: 3.95). 10/2006; 72(9):6331-44. DOI: 10.1128/AEM.00813-06
Source: PubMed

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.

0 Bookmarks
 · 
102 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Keratin biosorbents were prepared by reprocessing the deposits produced from chicken feathers after soluble keratin extraction. Biosorption of Cr(VI) ions onto the obtained biosorbents from aqueous solution was studied. Experimental factors affecting biosorption process such as pH and initial concentration of Cr(VI) ions were investigated. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were used to describe the biosorption process for Cr(VI) ions. The results showed that Langmuir model better fit the experimental data than the Freundlich and D–R models, and the maximum monolayer biosorption capacity for Cr(VI) ions was found to be 21.35 mg/g at pH 6, 200 mg/L initial concentration of Cr(VI) ions and 30°C. The free energy was calculated as 11.35 kJ/mol from the D–R model, indicating that the biosorption of Cr(VI) occurred chemically. This result was also confirmed by scanning electron microscopy and Fourier transform IR regarding the changes in morphology and surface structure of the biosorbents before and after Cr(VI) biosorption. Overall, the deposits generated from chicken feathers after soluble keratin extraction, which currently treated as wastes, should be regarded as a favorable alternative for the removal of Cr(VI) ions from aqueous solution.
    CLEAN - Soil Air Water 03/2014; · 2.05 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Chromium pollution is potentially detrimental for bacterial soil communities compromising carbon and nitrogen cycles that are essential for earth' s life. It has been proposed that intracellular reduction of hexavalent [Cr(VI)] to trivalent [Cr(III)] chromium may cause bacterial death by a mechanism that involves radical oxygen species (ROS)-induced DNA damage; the molecular basis of this phenomenon was investigated in this work. Here, we report that Bacillus subtilis cells lacking a functional error prevention oxidized guanine system (GO), were significantly more sensitive to Cr(VI) treatment than cells of the WT strain suggesting that oxidative damage to DNA is involved in the deleterious effects of this oxyanion. In agreement with this suggestion, Cr(VI) dramatically increased ROS concentration and induced mutagenesis in the GO-deficient B. subtilis strain. Alkaline gel electrophoresis (AGE) analysis of chromosomal DNA of WT and ΔGO mutant strains subjected to Cr(VI) treatment revealed that the DNA of the ΔGO strain was more susceptible to DNA glycosylase Fpg attack, suggesting that chromium genotoxicity is associated with 8-oxo-G lesions. In support of this notion, specific monoclonal antibodies detected the accumulation of 8-oxo-G lesions in the chromosome of B. subtilis cells subjected to Cr(VI) treatment. We conclude that Cr(VI) promotes mutagenesis and cell death in B. subtilis by a mechanism that involves radical oxygen attack of DNA generating 8-oxo-G and that such effects are counteracted by the preventive and repair GO system.
    Applied and Environmental Microbiology 06/2014; · 3.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Geobacter species often play an important role in the in situ bioremediation of uranium-contaminated groundwater, but little is known about how these microbes avoid uranium toxicity. To evaluate this further, the proteome of G. sulfurreducens exposed to 100 µM U(VI) acetate was compared with control cells not exposed to U(VI). Of the 1363 proteins detected from these cultures, 203 proteins had higher abundance during exposure to U(VI) compared to the control cells and 148 proteins had lower abundance. U(VI)-exposed cultures expressed lower levels of proteins involved in growth, protein and amino acid biosynthesis, as well as key central metabolism enzymes as a result of the deleterious effect of U(VI) in the growth of G. sulfurreducens. In contrast, proteins involved in detoxification, such as several efflux pumps belonging to the RND family, and protection of membrane and proteins, such as chaperons and proteins involved in secretion systems, were in higher abundance in cells exposed to U(VI). Exposing G. sulfurreducens to U(VI) resulted in higher abundance of many proteins associated with the oxidative stress response, such as superoxide dismutase and superoxide reductase. A strain in which the gene for superoxide dismutase was deleted grew slower than the wild-type strain in the presence U(VI), but not in its absence. The results suggest that there is not one specific mechanism for uranium detoxification. Rather, multiple general stress responses are induced, which presumably enable Geobacter species to tolerate high uranium concentrations.
    Microbiology 10/2014; · 2.84 Impact Factor

Full-text (2 Sources)

Download
35 Downloads
Available from
May 31, 2014