18] Measurements of softness of microbial cell surfaces

Abstract

Publisher Summary This chapter compares the dependence of the electrophoretic mobility on the ionic strength of a fibrillated and a nonfibrillated oral streptococcal strain. It reports that a soft, ion-penetrable strain was fibrillated, while an electrophoretically harder strain was devoid of a proteinaceous fibrillar surface layer, demonstrable by electron microscopy after negative staining. The bald streptococcal strain had a diffusion coefficient, as measured by dynamic light scattering that was independent of ionic strength and composition of the suspending fluid. The fibrillar strain shows an almost twofold decrease in diffusion coefficient on increasing the suspension pH from 2 to 7. Direct probing of the softness of microbial cell surfaces has been described using atomic force microscopy and suggested that the mechanical softness of microbial cell surfaces related with the electrophoretic one and the dynamic nature of microbial cell surfaces upon changes of their ionic environment. Thus, particulate microelectrophoresis, dynamic light scattering, and atomic force microscopy have become valuable, partly complementary methods to assess the softness and related ion penetrability of microbial cell surfaces. Considering the implications of these dynamic properties of microbial cell surfaces for their adhesion to surfaces, the chapter describes the application of these three methods as geared toward the analysis of microbial cell surfaces.