Flagellar Perturbations Activate Adhesion through Two Distinct Pathways in Caulobacter crescentus

Area of Science:

• Microbiology
• Bacterial Physiology
• Cellular Signaling

Background:

• Bacteria utilize sophisticated developmental programs for surface colonization.
• The rotary flagellum is crucial for bacterial motility and surface attachment.
• The precise signaling mechanisms by which flagella regulate adhesion are not fully understood.

Purpose of the Study:

• To investigate the role of flagellar signaling in regulating surface adhesion in Caulobacter crescentus.
• To identify genes and pathways involved in flagellum-mediated holdfast production.
• To elucidate how mechanical stimuli from the flagellum are integrated into the bacterial developmental program.

Main Methods:

• Genomewide phenotyping of wild-type and flagellar mutant Caulobacter crescentus strains.
• Epistasis analysis of flagellar signaling suppressor (fss) mutations.
• Characterization of flagellar assembly mutants and their effect on holdfast production.

Main Results:

• Identified flagellar mutations that enhance adhesion via a hyperholdfast phenotype and mutations that suppress this phenotype.
• Demonstrated that flagellum-stimulated holdfast production occurs via two distinct pathways: one developmental (PleD-dependent) and one mechanical (MotAB stator and DgcB-dependent).
• Assigned fss genes to specific pathways and identified novel motility genes regulating holdfast production.

Conclusions:

• The flagellum acts as a signaling hub, integrating mechanical and developmental signals to coordinate bacterial surface colonization.
• Two parallel pathways, one developmental and one mechanical, converge downstream of the flagellum to regulate adhesion.
• Signal integration is essential for linking environmental stimuli to complex bacterial behaviors like surface attachment.