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

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.The metal oxyanion chromate (CrO 4 2Ϫ ) is a widespread environmental contaminant due to its prevalent use in industrial and defense applications such as tanning, electroplating, paint pigment manufacturing, stainless steel welding, and nuclear weapons production (25,26). The hexavalent form of chromium, Cr(VI), is highly soluble and toxic, with chronic exposure leading to mutagenesis and carcinogenesis. Cr(VI)-induced apoptosis, for example, was demonstrated in p53 human bronchoalveolar cells (46), and Cr(VI) exposure results in a spectrum of genomic damage in cultured cells including DNA single-strand and double-strand breaks, binding of amino acids and proteins to DNA, DNA interstrand crosslinks, and Cr-DNA adducts (11,27,28,43,47,53,59,64,65). Cr toxicity is also associated with the generation of reactive oxygen intermediates during the intracellular partial reduction of Cr(VI) to the unstable intermediate Cr(V) by various in vivo nonspecific reductants (e.g., glutathione, NADH, NADPH, and cysteine) or cellular one-electron reductases (16,27,50). The other most stable, common form of chromium, trivalent Cr(III), is considered less toxic than Cr(VI) because of its tendency to form insoluble hydrated Cr 3ϩ complexes, which cannot cross cell membranes. However, Cr(III) was shown to cause DNA damage and inhibit topoisomerase DNA relaxation activity in bacteria (40).The adverse biological impact of Cr(VI) is attributable to the cellular uptake process. Chromate is transported across eukaryotic and prokaryotic cellular membranes vi...

Sustainable syntrophic growth of Dehalococcoides ethenogenes strain 195 with Desulfovibrio vulgaris Hildenborough and Methanobacterium congolense: global transcriptomic and proteomic analyses

“…Peptide identifications were filtered and sorted into proteins with DTASelect (Tabb et al, 2002) as described previously (VerBerkmoes et al, 2009). Contrast (Tabb et al, 2002) was used to display all proteins across runs, differentially expressed proteins were identified based on the following criteria (Chourey et al, 2006): at least under one condition, 440% sequence coverage, more than five unique peptides and X2-fold difference in spectral counts identified between DE195/DVH and DE195 isolate. Data identification as well as the actual MS/MS spectra from every peptide and accessory scores are available at http://compbio.ornl.gov/Dehalo195_CoCulture/.…”

Extracellular Reduction of Hexavalent Chromium by Cytochromes MtrC and OmcA of Shewanella oneidensis MR-1

“…In fact, 10% of the National Priorities List (Superfund sites) contain Cr(VI), and Cr(VI) is also a major contaminant found at the U.S. Department of Energy's Hanford Site in eastern Washington (7). Widespread Cr(VI) contamination poses major health concerns for the local environment and biota ranging from microorganisms to humans (1,4,10,29). Thus, environments contaminated with Cr(VI) need to be remediated to mitigate the harmful effects of Cr(VI).…”

Genome Sequencing Revealed Chromium and Other Heavy Metal Resistance Genes in E. cloacae B2-Dha

“…However, chromium has multiple effects on bacteria including competitive inhibition of sulphate transport, DNA mutagenesis and protein damage [8]. Microorganisms have developed various mechanisms to survive chromium toxicity: (i) transmembrane efflux of chromate (ii) the ChrR transport system (iii) the reduction of chromate (iv) protection against oxidative stress and (v) DNA repair systems [3,[9][10][11][12][13][14][15]. In addition, chromate resistance is attributed to the functions of a series of chromosomal or plasmid encoded genes, including the chromium resistance (chr) operon comprising of either chrBAC or chrBACF in bacteria [9,16,17].…”

“…In particular, chromium toxicity is generated through widespread anthropogenic activity via leather processing, steel production, wood preservation, chromium/electroplating, metal processing, alloy formation, textiles, ceramics and thermonuclear weapons manufacturing, and together with agronomic practices such as the use of organic biomass (sewage sludge or fertilizers), which continues to be a major threat to the environment [2][3][4][5][6]. Furthermore, chromium exerts damage directly on human health through toxic and mutagenic effects causing severe DNA damage [7].…”