(162ad) Rheology of Bacterial Films at Hexadecane-Water Interface

Assembly of bacterial cells at hydrocarbon-water interfaces (such as in oil/water emulsions) is important in applications such as bioremediation and microbial enhanced oil recovery. Although much is known about effects on the oil/water interface of various extracellular compounds released by certain bacteria, the influence of intact bacterial cells on the physical properties of the bacterial films (e.g. modification of oil-water interfacial tension and creation of surface viscoelasticity) remains a largely unexplored subject. In this study, the interfacial rheology of bacterial films was examined using the dynamic pendant drop technique. The bacterial films were formed through adsorption of a hydrophobic bacterial strain (Acinetobacter venetianus RAG-1) at a hexadecane-water interface. When in their stationary phase, the cells appeared to have no effect on the equilibrium interfacial tension as they accumulated at the interface. Upon transient excitation, however, the biofilms exhibited ?non-linear? rheological properties, in a sense that it repsonded differently to positive and negative area changes. In particular, the interface behaved as a viscous surface when subjected to sudden dilation, but showed clear signs of two-dimensional elasticity when the interfacial area was reduced. Using micropipettes, the local response of the cell layers to physical perturbations was also examined. A correlation could be seen between the interlocking of bacteria on the microscale and the wrinkling of the interface on the millimeter scale. These observations suggest that the transient behavior of the oil water interface can be dramatically altered by adsorption of bacteria, which may in turn affect emulsion formation and mobility of oil phases in porous media.