Kinetic analysis of ammonium sulfate dependent aggregation of bacteria

Solutions of ammonium sulfate (AMS) have been found to aggregate bacteria in a quantifiable and reproducible manner. The rates of aggregation promoted by the AMS of several bacteria obeyed pseudo-first-order kinetics. There was a high correlation between the rate of AMS aggregation of bacteria and the rate of adhesion to hexadecane by the bacteria. Rates of aggregation depended on AMS concentration, cell age, bacterial growth conditions and density of the cell suspension. Plots of rate constants of aggregation by AMS against AMS concentrations gave "S" shaped curves, implying cooperative effects. Addition of mannose did not alter the rate of AMS dependent aggregation of a Fim A strain of Escherichia coli, suggesting that ligands on the surface proteins do not interfere with the process of aggregation. Previous studies have implied that the slide aggregation of bacteria by AMS solutions reflects bacterial hydrophobocity. It is now proposed that rate constant determinations, based on loss of opacity of cellular suspensions in AMS, constitute a convenient means of studying bacterial hydrophobicity.