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  • 1
    Electronic Resource
    Electronic Resource
    Efflux of chromate by Pseudomonas aeruginosa cells expressing the ChrA protein (2002)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 212 (2002), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The ChrA protein of Pseudomonas aeruginosa plasmid pUM505 confers resistance to chromate. Using an in vitro system, we reported [Alvarez, A.H. et al. (1999) J. Bacteriol. 181, 7398–7400] that chromate resistance is based on energy-dependent efflux of chromate. It is shown here that ChrA determines in vivo efflux of 51CrO42− as well. Chromate-loaded cell suspensions of P. aeruginosa strain PAO1 harboring recombinant plasmid pEPL1, which expresses the ChrA protein, showed accelerated efflux of 51CrO42− as compared to the plasmidless chromate-sensitive derivative. After a 10-min loading, about 40% of 51CrO42− was lost from resistant cells in 15 min. Chromate efflux by resistant cells showed a typical saturation kinetics with an apparent Km of 82±11 μM chromate and a Vmax of 0.133±0.009 nmol chromate min−1 (mg protein)−1. Oxyanions sulfate and molybdate inhibited chromate efflux in a concentration-dependent fashion, whereas arsenate and ortho-vanadate had no significant effect on chromate release. Inhibition of chromate extrusion by valinomycin, nigericin, and carbonyl cyanide m-chlorophenylhydrazone, but not by oligomycin or dicyclohexylcarbodiimide, indicated that chromate efflux was driven by the membrane potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.2002.tb11274.x
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  • 2
    Electronic Resource
    Electronic Resource
    Essential residues in the chromate transporter ChrA of Pseudomonas aeruginosa (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 232 (2004), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The chrA gene of Pseudomonas aeruginosa plasmid pUM505 encodes the hydrophobic protein ChrA, which confers resistance to chromate by the energy-dependent efflux of chromate ions. Chromate-sensitive mutants were isolated by in vivo random mutagenesis. Transport experiments with cell suspensions of selected mutants showed that 51CrO42− extrusion was drastically lowered as compared to suspensions of the strain with the wild-type plasmid, confirming that the mutations affected a chromate efflux system. DNA sequence analysis showed that most point mutations affected amino acids clustered in the N-terminal half of ChrA, altering either cytoplasmic regions or transmembrane segments, and replaced residues moderately to highly conserved in ChrA homologs. PhoA and LacZ translational fusions were used to confirm the membrane topology at the N-terminal half of the ChrA protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0378-1097(04)00068-0
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  • 3
    Electronic Resource
    Electronic Resource
    Chromate-resistance in a chromate-reducing strain of Enterobacter cloacae (1990)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 67 (1990), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Resistance to toxic hexavalent chromium (chromate: CrO42−_ in Enterobacter cloacae strain HO1, isolated from an activated sludge sample, was investigated under aerobic and anaerobic conditions. Decreased uptake of 51CrO42− in E. cloacae strain HO1 was observed under aerobic conditions, when compared with a standard laboratory E. cloacae strain (IAM 1624). Under anaerobic conditions E. cloacae strain HO1 was able to reduce hexavalent chromium to the less toxic trivalent form. When E. clocacae strain HO1 was grown with nitrate anaerobically, the cells were observed to lose simultaneously their chromate-reducing ability and chromate-resistance under anaerobic conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1990.tb13841.x
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  • 4
    Electronic Resource
    Electronic Resource
    Plasmid-determined resistance to chromate in Pseudomonas aeruginosa (1988)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 56 (1988), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Resistance to chromate in five independent Pseudomonas aeruginosa clinical isolates was transferred by conjugation to P. aeruginosa strain PU21. All chromate-resistant transconjugants contained large plasmids that also conferred resistance to inorganic mercury. One of these plasmids, pUM505, increased the resistance to CrO42− and decreased the accumulation of intracellular 51CrO42− by the host cells as compared to the plasmidless strain PU21.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1988.tb03172.x
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  • 5
    Electronic Resource
    Electronic Resource
    Resistance to arsenic compounds in microorganisms (1994)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 15 (1994), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: Arsenic ions, frequently present as environmental pollutants, are very toxic for most microorganisms. Some microbial strains possess genetic determinants that confer resistance. In bacteria, these determinants are often found on plasmids, which has facilitated their study at the molecular level. Bacterial plasmids conferring arsenic resistance encode specific efflux pumps able to extrude arsenic from the cell cytoplasm thus lowering the intracellular concentration of the toxic ions. In Gram-negative bacteria, the efflux pump consists of a two-component ATPase complex. ArsA is the ATPase subunit and is associated with an integral membrane subunit, ArsB. Arsenate is enzymatically reduced to arsenite (the substrate of ArsB and the activator of ArsA) by the small cytoplasmic ArsC polypeptide. In Gram-positive bacteria, comparable arsB and arsC genes (and proteins) are found, but arsA is missing. In addition to the wide spread plasmid arsenic resistance determinant, a few bacteria confer resistance to arsenite with a separate determinant for enzymatic oxidation of more-toxic arsenite to less-toxic arsenate. In contrast to the detailed information on the mechanisms of arsenic resistance in bacteria, little work has been reported on this subject in algae and fungi.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6976.1994.tb00145.x
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  • 6
    Electronic Resource
    Electronic Resource
    Interactions of chromium with microorganisms and plants (2001)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 25 (2001), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6976.2001.tb00581.x
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  • 7
    Electronic Resource
    Electronic Resource
    Copper resistance mechanisms in bacteria and fungi (1994)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 14 (1994), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract: Copper is both an essential micronutrient and a toxic heavy metal for most living cells. The presence of high concentrations of cupric ions in the environment promotes the selection of microorganisms possessing genetic determinants for copper resistance. Several examples of chromosomal and plasmid copper-resistance systems in bacteria have been reported, and the mechanisms of resistance have started to be understood at the molecular level. Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced effiux of cupric ions, or copper complexation by cell components. Copper tolerance in fungi has also been ascribed to diverse mechanisms involving trapping of the metal by cell-wall components, altered uptake of copper, extracellular chelation or precipitation by secreted metabolites, and intracellular complexing by metallothioneins and phytochelatins; only the metallothionein chelation mechanism has been approached with molecular detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6976.1994.tb00083.x
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  • 8
    Electronic Resource
    Electronic Resource
    Microbial interactions with aluminium (1996)
    Springer
    BioMetals 9 (1996), S. 311-316 
    Details
    ISSN: 1572-8773
    Keywords: aluminium ; interaction ; microbe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Although aluminium is the most abundant metal in the Earth's crust, it lacks biological functions and shows a low bioavailability. Acid rain, however, solubilizes aluminium to toxic levels. Most research on the biological effects of aluminium has been centred on the analysis of aluminium-tolerant plants as well as its possible relationship with neurological disorders in humans. Also, several studies have been reported concerning aluminium effects on microorganisms, with more interest directed to cyanobacteria, soil bacteria and mycorrhizal fungi. Competition with iron and magnesium, and binding to DNA, membranes or cell walls are considered the main toxic effects of aluminium in microbes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00817932
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  • 9
    Electronic Resource
    Electronic Resource
    Bacterial interactions with chromate (1991)
    Springer
    Antonie van Leeuwenhoek 59 (1991), S. 229-233 
    Details
    ISSN: 1572-9699
    Keywords: bacterial detoxification ; chromate ; resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Hexavalent chromium compounds (chromates and dichromates) are highly toxic and are considered as mutagens and carcinogens. These compounds are discharged frequently to the environment as a result of diverse industrial processes. Some microorganisms are able to reduce hexavalent chromium to the less toxic trivalent form. Chromate pollution has promoted the selection of bacterial strains possessing chromate resistance determinants, usually carried by plasmids. Strains combining both abilities, i.e. resistance to and reduction of chromate, are potentially useful for detoxifying chromate polluted waste waters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583675
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  • 10
    Electronic Resource
    Electronic Resource
    Inorganic-ion resistance by bacteria isolated from a Mexico City freeway (1995)
    Springer
    Antonie van Leeuwenhoek 67 (1995), S. 333-337 
    Details
    ISSN: 1572-9699
    Keywords: bacteria ; resistance ; lead ; arsenate ; cadmium ; chromate ; mercury
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Bacteria were isolated from soil samples, containing high exchangeable lead concentrations, obtained from a busy freeway in the México City metropolitan area. Forty-five selected strains (86.7% Gram-positive) had a single MIC distribution pattern for lead (800–1600 µg/ml lead nitrate) and were considered lead-resistant. The isolates showed variable levels of resistance to arsenate (86.7%), chromate (66.7%), cadmium (57.6%), and mercury (31.1%) ions. Multiple inorganic-ion resistance was shown by all strains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00872931
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