Characterization of surface properties of bacterial spores using optical tweezers

The electric charge and the hydrodynamic coefficient and of bacterial spores are key parameters in protein binding to spores and in the adhesion of spores onto surfaces. Using Optical Tweezers, it is possible to simultaneously measure the charge and the hydrodynamic coefficient of a trapped object. From an accurate analysis of the motion of a single spore confined by an optical trap when external electric or drag forces are applied, we measured the charge of Bacillus subtilis spores. These were purified from a wild type strain and from two isogenic mutants characterized by an altered spore surface. Our technique is able to discriminate the three spore types used and to give important information on the hydrophobic properties of their surface.