Xylella fastidiosa outer membrane vesicles modulate plant colonization by blocking attachment to surfaces

Area of Science:

• Microbiology
• Plant Pathology
• Bacterial Pathogenesis

Background:

• Outer membrane vesicles (OMVs) are produced by Gram-negative bacteria and are known to deliver virulence factors.
• Their widespread production suggests roles beyond pathogenesis, such as stress response or cargo transport.
• Xylella fastidiosa is a xylem-colonizing bacterium that causes plant diseases.

Purpose of the Study:

• To investigate the role of OMVs produced by Xylella fastidiosa in bacterial-surface interactions.
• To determine the effect of quorum sensing on OMV production and bacterial adhesion.
• To understand how OMVs influence X. fastidiosa virulence and spread within host plants.

Main Methods:

• Analysis of OMV production in X. fastidiosa wild-type and mutant strains.
• Quantification of OMVs in xylem sap of infected plants.
• Assessing bacterial attachment to glass and plant surfaces in the presence and absence of OMVs.
• Investigating the role of the diffusible signal factor-dependent quorum-sensing system.

Main Results:

• X. fastidiosa OMVs were found to block the bacterium's interaction with surfaces, including xylem vessel walls.
• OMV release was suppressed by the quorum-sensing system; a ΔrpfF mutant showed reduced adhesion and increased virulence.
• The ΔrpfF mutant produced fivefold more OMVs and exhibited 20-fold lower attachment frequency to xylem vessels when OMVs were present.

Conclusions:

• OMV production by X. fastidiosa is a strategy to regulate surface attachment, facilitating systemic spread within the plant host.
• This mechanism allows X. fastidiosa to transition from an adhesive state (for insect transmission) to an exploratory lifestyle.
• OMVs may aid the movement of other bacteria in porous environments by reducing surface contact.