Number fluctuation spectroscopy of motile microorganisms

Area of Science:

• Microbiology
• Biophysics
• Statistical Mechanics

Background:

• Bacterial motility is crucial for survival and colonization.
• Understanding bacterial movement dynamics requires accurate biophysical models.
• Quantifying bacterial swimming speed and persistence length is key to characterizing motility.

Purpose of the Study:

• To develop and validate a random-walk model for predicting bacterial number fluctuations.
• To establish number fluctuations as a quantitative measure of bacterial motility parameters.
• To investigate the influence of different bacterial strains and their movement patterns on these fluctuations.

Main Methods:

• Utilized a random-walk model to simulate particle number fluctuations in a defined volume.
• Employed dynamic light scattering (DLS) to experimentally measure scattered light intensity correlation functions.
• Analyzed experimental data from three strains of Escherichia coli with varying motility characteristics.

Main Results:

• Demonstrated that number fluctuations quantitatively correlate with mean swimming speed and persistence length.
• Achieved excellent agreement between the random-walk model predictions and experimental data for a highly persistent E. coli strain.
• Observed deviations in more erratic strains, indicating additional contributions from orientational fluctuations.

Conclusions:

• Bacterial number fluctuations are a robust indicator of motility parameters like speed and persistence.
• The random-walk model provides a valuable theoretical framework for analyzing bacterial movement.
• Orientational fluctuations can significantly impact scattering data in less persistent bacterial populations.