Bacterial surface motility is modulated by colony-scale flow and granular jamming

Area of Science:

• Microbiology
• Biophysics
• Cell Biology

Background:

• Microbes like Bacillus subtilis migrate collectively on wet surfaces in thin water layers.
• This collective migration is crucial for acquiring territory and resources.
• Previous studies identified surfactant secretion and surface water as key requirements.

Purpose of the Study:

• To investigate the physical mechanisms governing Bacillus subtilis collective migration.
• To understand the role of water availability in modulating group motility.
• To explore the self-organization and movement dynamics of migrating microbial groups.

Main Methods:

• Observation of Bacillus subtilis groups under varying water availability conditions.
• Analysis of cellular packing fraction and fluid flow within migrating groups.
• Microscopy and genetic analysis to study group behavior and structure.

Main Results:

• Water availability acts as a critical parameter controlling a jamming-like transition, determining group fluidity and motility.
• Migrating groups self-organize into distinct layers.
• Collective motility is driven by pulling from the front, not requiring cell proliferation.
• Internal flow within groups transports material from the colony to the leading edge.

Conclusions:

• Physical properties, including cellular packing and flow, regulate microbial collective migration from cellular to centimeter scales.
• Understanding these physical principles is key to comprehending microbial expansion and colonization.
• Water availability is a crucial environmental factor influencing microbial collective behavior and spatial expansion.