Characterization of cell surface and extracellular matrix remodeling of Azospirillum brasilense chemotaxis-like 1 signal transduction pathway mutants by atomic force microscopy

Authors

  • Amanda Nicole Edwards,

    1. Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, USA
    2. Oak Ridge National Laboratory, Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, USA
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  • Piro Siuti,

    1. Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, USA
    2. Oak Ridge National Laboratory, Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, USA
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  • Amber N. Bible,

    1. Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, USA
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  • Gladys Alexandre,

    1. Oak Ridge National Laboratory, Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, USA
    2. Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, USA
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  • Scott T. Retterer,

    1. Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, USA
    2. Oak Ridge National Laboratory, Center for Nanophase Materials Sciences, Oak Ridge, TN, USA
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  • Mitchel J. Doktycz,

    1. Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, USA
    2. Oak Ridge National Laboratory, Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, USA
    3. Oak Ridge National Laboratory, Center for Nanophase Materials Sciences, Oak Ridge, TN, USA
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  • Jennifer L. Morrell-Falvey

    1. Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN, USA
    2. Oak Ridge National Laboratory, Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, USA
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  • Editor: Yaacov Okon

Correspondence: Jennifer L. Morrell-Falvey, Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN 37831, USA. Tel.: +1 865 241 2841; fax: +1 865 574 5345; e-mail: morrelljl1@ornl.gov

Abstract

To compete in complex microbial communities, bacteria must sense environmental changes and adjust cellular functions for optimal growth. Chemotaxis-like signal transduction pathways are implicated in the regulation of multiple behaviors in response to changes in the environment, including motility patterns, exopolysaccharide production, and cell-to-cell interactions. In Azospirillum brasilense, cell surface properties, including exopolysaccharide production, are thought to play a direct role in promoting flocculation. Recently, the Che1 chemotaxis-like pathway from A. brasilense was shown to modulate flocculation, suggesting an associated modulation of cell surface properties. Using atomic force microscopy, distinct changes in the surface morphology of flocculating A. brasilense Che1 mutant strains were detected. Whereas the wild-type strain produces a smooth mucosal extracellular matrix after 24 h, the flocculating Che1 mutant strains produce distinctive extracellular fibril structures. Further analyses using flocculation inhibition, lectin-binding assays, and comparison of lipopolysaccharides profiles suggest that the extracellular matrix differs between the cheA1 and the cheY1 mutants, despite an apparent similarity in the macroscopic floc structures. Collectively, these data indicate that disruption of the Che1 pathway is correlated with distinctive changes in the extracellular matrix, which likely result from changes in surface polysaccharides structure and/or composition.

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