Accuracy of RGD approximation for computing light scattering properties of diffusing and motile bacteria

Area of Science:

• Biophysics
• Microbiology
• Optical Physics

Background:

• Quasi-elastic light scattering (QELS) is a key technique for characterizing bacterial motility.
• Interpretations of QELS data typically rely on the Rayleigh-Gans-Debye (RGD) approximation.
• The validity of RGD for bacteria larger than the light wavelength is uncertain.

Purpose of the Study:

• To develop and apply rigorous scattering theory for QELS analysis of bacterial motility.
• To assess the accuracy of the RGD approximation for bacterial size and optical properties.
• To investigate polarized and depolarized light scattering from motile bacteria.

Main Methods:

• Formulated a method using rigorous scattering theory for QELS intensity and spectra.
• Employed numerical solutions of scattering field amplitudes for a prolate spheroid model of E. coli.
• Computed polarized and depolarized scattered light intensity, and field correlation functions for various motion models.

Main Results:

• Calculated polarized scattered light intensity, polarized field correlation functions, and depolarized components.
• Investigated sensitivity to variations in refractive index and bacterial size.
• Found RGD approximation accuracy within 10% for E. coli under typical conditions for intensity and polarized correlation functions.

Conclusions:

• Rigorous scattering theory provides a robust framework for QELS analysis of bacterial motility.
• The RGD approximation is sufficiently accurate for E. coli characterization within a reasonable parameter range.
• Depolarized scattering contributions are generally minimal for E. coli.