Cell surface properties correlated with cohesion in Myxococcus xanthus

Area of Science:

• Microbiology
• Cell Biology
• Bacterial Motility

Background:

• Myxococcus xanthus gliding behavior is regulated by two multigene systems: A (adventurous) and S (social).
• The S system controls social behaviors, including cell agglutination, and can be disrupted by mutation (e.g., dsp mutation) or Congo red treatment.
• Cell surface topology changes correlate with altered cohesive properties in S+ cells.

Purpose of the Study:

• To investigate the role of cell-associated appendages in Myxococcus xanthus cell cohesion.
• To understand the mechanism by which the S system regulates cell-cell interactions.
• To explore the relationship between fibril secretion and cell agglutination.

Main Methods:

• Observation of cell-associated appendages (thin fimbriae/pili and thick fibrils) using electron microscopy.
• Genetic disruption of the S system (dsp mutation) and phenotypic disruption using Congo red.
• Assessing cell agglutination and extracellular matrix formation.
• Quantifying cell collision efficiency and its dependence on cell density.

Main Results:

• Wild-type cells exhibit thin fimbriae and thick fibrils; thick fibrils coat the cell surface and form an extracellular matrix.
• Dsp mutants and Congo red-treated cells failed to agglutinate and did not secrete extracellular fibrils.
• Congo red removal restored both cohesion and thick fibril production in wild-type cells.
• Cell collision efficiency was high (1 in 3 optimal) but decreased linearly with increasing cell density.

Conclusions:

• Thick fibrils are essential for Myxococcus xanthus cell cohesion and social behavior.
• The S system regulates cohesion through the secretion of these thick fibrils.
• Cell density influences cohesion, suggesting a regulatory mechanism for cell-cell interactions.