Rhizobial Surface Biopolymers and their Interaction with Lectin Measured by Atomic Force Microscopy

Atomic force microscopy (AFM) was used to measure the morphology and physicochemical properties of rhizobia and to probe cell-surface polymers with tips modified with soybean agglutinin (SBA). AFM measurements of the length, width, and height of Sinorhizobium fredii CCRC15769 were 1580±450, 870±70, and 270±50 nm, respectively (means±SD). Different AFM image modes revealed the morphology, adhesion, viscoelasticity, and surface roughness of rhizobia in air using the tapping operation. Force–distance relationships between SBA-terminated AFM probes and Bradyrhizobium japonicum USDA110 were recorded and the retraction curves showed an unbinding force of 106±48 pN with a loading rate of 1 nN/s in PBS containing 0.1 mM Mn2+ and 0.1 mM Ca2+ (pH 7.2). The technique of AFM provides information about the morphology and molecular interaction forces of rhizobia under physiological conditions.