Collective bacterial dynamics revealed using a three-dimensional population-scale defocused particle tracking...

Area of Science:

• Microbiology
• Biophysics
• Cellular Dynamics

Background:

• Understanding bacterial locomotion, including biofilm formation, chemotaxis, and virulence, requires monitoring cell movement and collective dynamics.
• Previous methods often lack the resolution or dimensionality to fully capture complex bacterial motility patterns.

Purpose of the Study:

• To introduce and validate a novel three-dimensional (3D) defocused particle tracking (DPT) method for high-resolution analysis of bacterial locomotion.
• To differentiate and quantify the motility characteristics of wild-type Escherichia coli and mutant strains with altered chemotaxis pathways.

Main Methods:

• Employed a novel 3D defocused particle tracking (DPT) technique to capture single-cell trajectories of swimming bacteria in three spatial dimensions.
• Generated 3D trajectories for wild-type Escherichia coli (RP437), a smooth-swimming mutant (cheA deletion, RP9535), and a tumbling mutant (cheZ deletion, RP1616).
• Calculated diffusion coefficients for each bacterial strain based on their 3D movement patterns.

Main Results:

• The 3D DPT method successfully distinguished between wild-type, smooth-swimming, and tumbling bacterial locomotion modes.
• Smooth-swimming bacteria exhibited a diffusion coefficient approximately two orders of magnitude higher than tumbling bacteria.
• Diffusion coefficients increased with higher bacterial cell densities, suggesting hydrodynamic interactions influence bacterial movement.

Conclusions:

• The 3D DPT method provides a powerful tool for detailed analysis of bacterial motility and collective dynamics.
• Chemotaxis mutations significantly alter bacterial diffusion rates, with smooth swimmers diffusing more readily than wild-type and tumblers.
• Cell density plays a crucial role in bacterial diffusion, likely mediated by hydrodynamic disturbances.