How bacterial cells and colonies move on solid substrates.

Area of Science:

• Microbiology
• Biophysics
• Computational Biology

Background:

• Bacteria utilize active cell appendages, like type IV pili, for substrate motility and cell-cell interactions.
• Experimental studies show *Neisseria gonorrhoeae* exhibits persistent random walk motility, influenced by pili length and number.

Purpose of the Study:

• To investigate the mechanisms driving bacterial cell and colony motility mediated by type IV pili.
• To determine if a simple tug-of-war model can explain persistent single-cell motion.
• To identify factors contributing to microcolony motility.

Main Methods:

• Development of a tractable stochastic model to simulate pili interactions and cell movement.
• Testing the tug-of-war hypothesis for single-cell persistent motion.
• Validation using a 3D computational model incorporating pili dynamics, force generation, and cell geometry.

Main Results:

• The stochastic model successfully reproduced persistent motion in individual *Neisseria gonorrhoeae* cells.
• A simple tug-of-war mechanism alone could not account for microcolony motility, which weakened with increased colony size.
• Inclusion of sliding friction between microcolonies and the substrate improved model accuracy for colony movement.

Conclusions:

• Persistent motion of single bacterial cells can emerge from a tug-of-war mechanism involving type IV pili.
• Microcolony motility is more complex and requires additional factors like sliding friction to be accurately modeled.
• The study provides a validated computational framework for understanding bacterial collective behaviors.