Ion Depletion in the Interfacial Microenvironment from Cell-Surface Interactions

The nanoscale region immediately adjacent to surfaces, although challenging to probe, is directly responsible for local chemical and physical interactions between a material and its surroundings. Cell-surface contacts are mediated by a combination of electrostatic and acid-base interactions that alter the local environment over time. In this study, a label-free vibrational probe with a nanometer length scale reveals that the electrostatic potential at a silica surface gradually increases in the presence of bacteria in solution. We illustrate that the cells themselves are not responsible for this effect. Rather, they alter the interfacial chemical environment in a manner that is consistent with a reduction of the ionic strength to a level that is roughly four times lower than that of the bulk aqueous phase.

Monitoring Early Stages of Bacterial Adhesion at Silica Surfaces through Image Analysis

Bacterial adhesion and biofilm formation on abiotic surfaces are important phenomena with industrial, environmental, and biological relevance. Recent findings using vibrational spectroscopy to study Escherichia coli (E. coli) K12 adhesion on silica indicated that interfacial water signals are linked to changes at the surface in the presence of bacteria. Although such techniques provide a unique glimpse into the surface microenvironment, the origin of the features tracked by the water signals remains to be identified. Here, we have used brightfield microscopy with enhanced image processing to study E. coli K12 adhering to silica. Although most of the clusters of cells on the surface are small, with many individual cells adhered throughout the exponential phase, the overall surface coverage was found to be dominated by clusters greater than 100 μm² in area. However, it is the adhesion profile of the small clusters that most closely matches the interfacial water signals, suggesting that surface-bound water changes immediately upon adhesion.