Probing Bacterial Electrosteric Interactions Using Atomic Force Microscopy

Abstract

Atomic force microscopy (AFM) was used to probe the effects of pH, ionic strength, and the presence of bacterial surface polymers on interaction forces between individual, negatively charged bacteria and silicon nitride. Bacterial surface polymers dominated interactions between bacteria and AFM silicon nitride tips. The measured forces were represented well by an electrosteric repulsion model accounting for repulsion between the tip and bacterial polymers but were much larger in magnitude and extended over longer distances (100’s of nanometers) than predicted by DLVO theory. The equilibrium length (Lo) of the polymers was allowed to vary with solution chemistry to account for intramolecular electrostatic interactions between individual polymer units. The effects of the variables pH and ionic strength on bacterial interaction forces were investigated independently. Pseudomonas putida KT2442 was studied