Genes encoding a cellulosic polymer contribute toward the ecological success of Pseudomonas fluorescens SBW25 on plant surfaces

Authors

  • Micaela Gal,

    1. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK,
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    • Present address: Anaerobe Reference Unit, PHLS, Department of Medical Microbiology, University Hospital of Wales, Cardiff CF14 4XW, UK;

  • Gail M. Preston,

    1. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK,
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  • Ruth C. Massey,

    1. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK,
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    • Present address: Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK

  • Andrew J. Spiers,

    1. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK,
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  • Paul B. Rainey

    Corresponding author
    1. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK,
    2. School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
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Paul Rainey. Fax: + 64 93737946; E-mail: p.rainey@auckland.ac.nz

Abstract

Pseudomonas fluorescens SBW25 is a Gram-negative bacterium that grows in close association with plants. In common with a broad range of functionally similar bacteria it plays an important role in the turnover of organic matter and certain isolates can promote plant growth. Despite its environmental significance, the causes of its ecological success are poorly understood. Here we describe the development and application of a simple promoter trapping strategy (IVET) to identify P. fluorescens SBW25 genes showing elevated levels of expression in the sugar beet rhizosphere. A total of 25 rhizosphere-induced (rhi) fusions are reported with predicted roles in nutrient acquisition, stress responses, biosynthesis of phytohormones and antibiotics. One rhi fusion is to wss, an operon encoding an acetylated cellulose polymer. A mutant carrying a defective wss locus was competitively compromised (relative to the wild type) in the rhizosphere and in the phyllosphere, but not in bulk soil. The rhizosphere-induced wss locus therefore contributes to the ecological performance of SBW25 in the plant environment and supports our conjecture that genes inactive in the laboratory environment, but active in the wild, are likely to be determinants of fitness in natural environments.

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