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Ultrastructural surface changes associated with dextran synthesis by Leuconostoc mesenteroides

B E Brooker

    Journal of Bacteriology
    |July 1, 1977
    PubMed
    Summary

    Leuconostoc mesenteroides forms a distinct cell surface coat and capsule when exposed to sucrose. This extracellular material, composed of dextran, is crucial for understanding bacterial polysaccharide production.

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    Area of Science:

    • Microbiology
    • Bacterial Cell Wall Ultrastructure
    • Extracellular Polysaccharide Synthesis

    Background:

    • Gram-positive bacteria possess a complex cell wall structure.
    • Bacterial surface structures play vital roles in cell-environment interactions.
    • Dextran synthesis by bacteria is influenced by substrate availability.

    Purpose of the Study:

    • To investigate the ultrastructural changes in Leuconostoc mesenteroides NCDO 1875 cell walls upon sucrose exposure.
    • To characterize the formation and composition of extracellular materials produced by this bacterium.
    • To elucidate the relationship between cell-bound enzymes and capsular polysaccharide production.

    Main Methods:

    • Growth of Leuconostoc mesenteroides in MRS broth.
    • Electron microscopy with ruthenium red fixation for ultrastructural analysis.
    • Cytochemical localization of periodate-reactive carbohydrates.

    Main Results:

    • A triple-layered cell wall was observed in untreated cells.
    • Exposure to sucrose induced a uniform, electron-dense surface coat (110-130 nm thick) within 2 hours.
    • A subpopulation of cells developed large, filamentous capsules (up to 6 µm) after prolonged sucrose exposure.
    • Periodate-reactive carbohydrates were identified in both the surface coat and capsule.

    Conclusions:

    • The surface coat likely represents a cell-bound dextran-dextransucrase complex.
    • The observed capsular dextran is an insoluble polysaccharide, while acapsulate cells may produce soluble dextran.
    • Sucrose availability triggers differential polysaccharide synthesis and extracellular matrix formation in Leuconostoc mesenteroides.

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