Taking advantage of electric field induced bacterial aggregation for the study of interactions between bacteria and macromolecules by capillary electrophoresis

International audience; The quantification of interaction stoechiometry and binding constant between bacteria (or other microorganism) and(macro)molecules remains a challenging issue for which only a few adapted methods are available. In this paper, a new methodologywas developed for the determination of the interaction stoichiometry and binding constant between bacteria and (macro)molecules. The originality of this work is to take advantage of the bacterial aggregation phenomenon to directly quantify the freeligand concentration in equilibrated bacteria-ligand mixtures using frontal analysis continuous capillary electrophoresis. The describedmethodology does not require any sample preparation such as filtration step or centrifugation. It was applied to the study ofinteractions between Erwinia carotovora and different generations of dendrigraft poly-L-lysines leading to quantitative informations(i.e. stoichiometry and binding site constant). High stoichiometries in the order of 106-107 were determined between nanometricdendrimer-like ligands and the rod-shaped micrometric bacteria. The effect of the dendrimer generation on the binding constantand the stoichiometry is discussed. Stoichiometries were compared with those obtained by replacing the bacteria by polystyrenemicrobeads to demonstrate the internalization of the ligands inside the bacteria and the increase of the specific surface via theformation of vesicles.