Light scattering characterization of bacterial morphology in aqueous suspension

We present a combined light scattering methodology for the ensemble-averaged characterization of bacterial morphology and size distributions directly in aqueous suspension. The approach integrates heterodyne near-field scattering with three-dimensional cross-correlation dynamic light scattering, providing continuous access to the scattered-intensity over an extended range of scattering vectors. This configuration enables simultaneous probing of length scales associated with both the axial and radial dimensions of bacterial cells. The measured intensity profiles exhibit form-factor features characteristic of spherocylindrical particles, including oscillatory behavior arising from finite particle geometry. To interpret the experimental data, the bacterial population is modeled as a polydisperse ensemble of randomly oriented spherocylinders. Orientational averaging and population heterogeneity are explicitly incorporated into the scattering model, allowing quantitative extraction of distributions of cell length and radius for multiple bacterial strains. The calculated form factors show good agreement with experimental measurements across the full scattering range, demonstrating sensitivity to both axial and transverse polydispersity. These results establish the combined scattering framework as a statistically robust method for characterizing bacterial morphology in suspension. The approach complements microscopy-based measurements and provides a quantitative experimental basis for physical modeling of bacterial systems relevant to biomedical, environmental, and industrial contexts.