Pseudomonas fluorescens' view of the periodic table

Authors

  • Matthew L. Workentine,

    1. Biofilm Research Group and
    2. Department of Biological Sciences, Faculty of Science, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada T2N 1N4.
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  • Joe J. Harrison,

    1. Biofilm Research Group and
    2. Department of Biological Sciences, Faculty of Science, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada T2N 1N4.
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  • Pernilla U. Stenroos,

    1. Biofilm Research Group and
    2. Department of Biological Sciences, Faculty of Science, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada T2N 1N4.
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    • Present address: Department of Biology, Abo Akademi University, BioCity, Artillerigatan 6, 20520 Turku, Finland.

  • Howard Ceri,

    1. Biofilm Research Group and
    2. Department of Biological Sciences, Faculty of Science, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada T2N 1N4.
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  • Raymond J. Turner

    Corresponding author
    1. Department of Biological Sciences, Faculty of Science, University of Calgary, 2500 University Dr NW, Calgary, AB, Canada T2N 1N4.
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*E-mail turnerr@ucalgary.ca; Tel. (+1) 403 2204308; Fax (+1) 403 289 9311.

Summary

Growth in a biofilm modulates microbial metal susceptibility, sometimes increasing the ability of microorganisms to withstand toxic metal species by several orders of magnitude. In this study, a high-throughput metal toxicity screen was initiated with the aim of correlating biological toxicity data in planktonic and biofilm cells to the physiochemical properties of metal ions. To this end, Pseudomonas fluorescens ATCC 13525 was grown in the Calgary Biofilm Device (CBD) and biofilms and planktonic cells of this microorganism were exposed to gradient arrays of different metal ions. These arrays included 44 different metals with representative compounds that spanned every group of the periodic table (except for the halogens and noble gases). The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum biofilm eradication concentration (MBEC) values were obtained after exposing the biofilms to metal ions for 4 h. Using these values, metal ion toxicity was correlated to the following ion-specific physicochemical parameters: standard reduction-oxidation potential, electronegativity, the solubility product of the corresponding metal–sulfide complex, the Pearson softness index, electron density and the covalent index. When the ions were grouped according to outer shell electron structure, we found that heavy metal ions gave the strongest correlations to these parameters and were more toxic on average than the other classes of the ions. Correlations were different for biofilms than for planktonic cells, indicating that chemical mechanisms of metal ion toxicity differ between the two modes of growth. We suggest that biofilms can specifically counter the toxic effects of certain physicochemical parameters, which may contribute to the increased ability of biofilms to withstand metal toxicity.

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