Emergence of bacterial glass

Area of Science:

• Physics of active matter
• Soft condensed matter physics
• Microbiology

Background:

• Densely packed, motile bacteria exhibit collective behaviors not observed in passive materials.
• Understanding these states is crucial for studying bacterial colonies, biofilms, and general material science.
• Previous challenges included creating uniformly growing, large, quasi-two-dimensional bacterial assemblies.

Purpose of the Study:

• To characterize the emergence of glassy states in two-dimensional suspensions of motile bacteria (Escherichia coli).
• To investigate the physical properties and dynamics of these bacterial glassy states.
• To compare bacterial glass properties with those of conventional thermal glasses.

Main Methods:

• Utilized a membrane-based microfluidic device to generate uniformly growing, large, quasi-two-dimensional bacterial assemblies.
• Employed statistical analyses to characterize bacterial populations at increasing densities.
• Conducted investigations of individual bacterial motion to analyze dynamic properties.

Main Results:

• Observed the emergence of glassy states in Escherichia coli suspensions as cell density increased.
• Identified a two-step transition to a glassy state: first suppressing orientational modes, then completely vitrifying motion.
• Found characteristic glass features (slowdown, heterogeneity, cage effects) alongside unique properties like micro-domain formation and unusual dynamic susceptibility signals.

Conclusions:

• Bacterial populations transition into a two-step glassy state with increasing density.
• Bacterial active glass exhibits distinct properties compared to thermal glass, including spontaneous micro-domain formation and density-dependent slowdown.
• These findings offer insights into the physical mechanisms governing dense bacterial aggregates and active matter systems.