Atomic force microscopy of a ctpA mutant in Rhizobium leguminosarum reveals surface defects linking CtpA function to biofilm formation

Abstract

Atomic force microscopy was used to investigate the surface ultrastructure, adhesive properties and biofilm formation ofRhizobium leguminosarumand actpAmutant strain. The surface ultrastructure of wild-typeR. leguminosarumconsists of tightly packed surface subunits, whereas thectpAmutant has much larger subunits with loose lateral packing. ThectpAmutant strain is not capable of developing fully mature biofilms, consistent with its altered surface ultrastructure, greater roughness and stronger adhesion to hydrophilic surfaces. For both strains, surface roughness and adhesive forces increased as a function of calcium ion concentration, and for each, biofilms were thicker at higher calcium concentrations.