Mechanical interactions govern self-organized ordering in bacterial colonies on surfaces

Area of Science:

• Microbiology
• Biophysics
• Computational Biology

Background:

• Bacterial colonies exhibit complex morphologies shaped by mechanical stresses.
• Understanding the interplay between cell growth, mechanical forces, and substrate interactions is crucial for predicting colony development.

Purpose of the Study:

• To investigate how mechanical factors like cell growth, steric interactions, and cell-substrate friction influence bacterial colony morphology and internal organization.
• To characterize the self-organization of bacterial communities under surface confinement.

Main Methods:

• Overdamped dynamics simulations of nonmotile, stress-responsive bacteria.
• Analysis of microdomain formation, area distribution, and nematic order parameter.
• Quantification of force transmission and stress distribution within colonies.

Main Results:

• Spontaneous formation of microdomains with highly aligned cells due to competing growth stresses and steric constraints.
• Substrate friction is a key determinant of domain size and orientational diversity.
• Mechanosensitive growth did not significantly alter domain structure in the biologically relevant range.
• Increased division length led to enhanced steric effects, slower shape relaxation, and broader force distribution.

Conclusions:

• Bacterial colony morphology and stress organization can arise from local mechanical interactions.
• Substrate interactions, proliferation dynamics, and stress-growth coupling collectively govern bacterial community self-organization on surfaces.