Invasion of insect cells by Spiroplasma citri involves spiralin relocalization and lectin/glycoconjugate-type...

Area of Science:

• Microbiology
• Cell Biology
• Molecular Biology

Background:

• Spiroplasma citri, a helical, wall-less bacterium (Mollicutes), infects plants and arthropods.
• Understanding how Spiroplasma citri invades insect cells is key to its transmission and pathogenicity.

Purpose of the Study:

• To investigate the role of the lipoprotein spiralin in Spiroplasma citri adhesion and invasion of insect cells.
• To elucidate the mechanism by which spiralin mediates early cell attachment.

Main Methods:

• Confocal laser scanning immunomicroscopy to visualize spiralin localization.
• Bacterial adhesion assays using wild-type and spiralin-less mutant strains.
• Recombinant spiralin-mediated latex bead adhesion assays.
• Lectin binding assays to analyze surface glycoconjugates and spiralin interactions.

Main Results:

• Spiralin relocalizes to the contact zone during Spiroplasma citri adhesion to insect cells.
• A spiralin-less mutant exhibits significantly reduced adhesion, while recombinant spiralin promotes adhesion.
• Cytochalasin D treatment enhances wild-type adhesion by exposing spiralin receptors, but not in the mutant.
• Spiralin displays binding properties similar to Vicia villosa agglutinin (VVA) lectin for insect cell glycoconjugates.

Conclusions:

• Spiralin is a major factor in the initial adhesion of Spiroplasma citri to insect cells.
• Spiralin mediates adhesion through direct or indirect binding to insect cell surface glycoconjugates.
• The findings reveal a key mechanism for pathogen entry into insect vectors.