Effect of Particulate Contaminants on the Development of Biofilms at Air/Water Interfaces

The development of biofilms at air/water or oil/water interfaces has important ramifications on several applications, but it has received less attention than biofilm formation on solid surfaces. A key difference between the growth of biofilms on solid surfaces versus liquid interfaces is the range of complicated boundary conditions the liquid interface can create that may affect bacteria, as they adsorb onto and grow on the interface. This situation is exacerbated by the existence of complex interfaces in which interfacially adsorbed components can even more greatly affect interfacial boundary conditions. In this work, we present evidence as to how particle-laden interfaces impact biofilm growth at an air/water interface. We find that particles can enhance the rate of growth and final strength of biofilms at liquid interfaces by providing sites of increased adhesive strength for bacteria. The increased adhesion stems from creating localized areas of hydrophobicity that protrude in the water phase and provide sites where bacteria preferentially adhere. This mechanism is found to be primarily controlled by particle composition, with particle size providing a secondary effect. This increased adhesion through interfacial conditions creates biofilms with properties similar to those observed when adhesion is increased through biological means. Because of the generally understood ubiquity of increased bacteria attachment to hydrophobic surfaces, this result has general applicability to pellicle formation for many pellicle-forming bacteria.