Possible role of reactive chlorine in microbial antagonism and organic matter chlorination in terrestrial environments

Authors

  • Per Bengtson,

    1. Department of Microbial Ecology, Lund University, Ecology Building, SE-223 62 Lund, Sweden.
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  • David Bastviken,

    1. Department of Geology and Geochemistry, Stockholm University, 106 91 Stockholm, Sweden.
    2. Department of Water and Environmental Studies, Linköping university, 581 83 Linköping, Sweden.
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  • Wietse De Boer,

    1. NIOO-KNAW, Centre for Terrestrial Ecology, P.O. Box 40, 6666 ZG Heter, en The Netherlands.
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  • Gunilla Öberg

    Corresponding author
    1. Institute for Resources, Environment and Sustainability, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
      *E-mail goberg@ires.ubc.ca; Tel. (+1) 604 822 3010; Fax (+1) 604 822 9250.
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*E-mail goberg@ires.ubc.ca; Tel. (+1) 604 822 3010; Fax (+1) 604 822 9250.

Summary

Several studies have demonstrated that extensive formation of organically bound chlorine occurs both in soil and in decaying plant material. Previous studies suggest that enzymatic formation of reactive chlorine outside cells is a major source. However, the ecological role of microbial-induced extracellular chlorination processes remains unclear. In the present paper, we assess whether or not the literature supports the hypothesis that extracellular chlorination is involved in direct antagonism against competitors for the same resources. Our review shows that it is by no means rare that biotic processes create conditions that render biocidal concentrations of reactive chlorine compounds, which suggest that extracellular production of reactive chlorine may have an important role in antagonistic microbial interactions. To test the validity, we searched the UniprotPK database for microorganisms that are known to produce haloperoxidases. It appeared that many of the identified haloperoxidases from terrestrial environments are originating from organisms that are associated with living plants or decomposing plant material. The results of the in silico screening were supported by various field and laboratory studies on natural chlorination. Hence, the ability to produce reactive chlorine seems to be especially common in environments that are known for antibiotic-mediated competition for resources (interference competition). Yet, the ability to produce haloperoxidases is also recorded, for example, for plant endosymbionts and parasites, and there is little or no empirical evidence that suggests that these organisms are antagonistic.

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