Role of macro and nanoscale interactions in bacterial attachment to heterogeneous surfaces

Bacterial transport and attachment to surfaces is of considerable importance to engineered and natural systems. Once bacteria associate with a surface, they develop into complex communities of cells encased in exopolymeric substances (EPS) forming a biofilm. Bacterial surface association and subsequent biofilm formation is governed by the initial attachment step. Initial attachment of pathogenic bacteria to environmentally and medically relevant substrata is governed by cell and substratum surface features, including nanoscale roughness, charge and surface chemistry, and the chemistry of the intervening fluid. This work sought to elucidate nanoscale contributions to macro-scale adhesive behavior from the standpoint of the bacterial cell surface and the substratum. Materials of varied surface chemistry and charge were tested as substrata for adhesive capacity towards Escherichia coli in macro-scale continuous-flow columns. Atomic force microscopy (AFM) was used to determine nano-scale interaction energies. Observed adhesive behavior between the test E. coli strains on the tested mineral surfaces, was consistent with surface analyses, conducted at both the macro- and nanoscale. The impact of substratum surface features such as height and roughness on adhesive interactions was examined in a well-defined AFM experiment. Intrinsic substrata surface properties (topography and chemistry) were modified by imaging conditions (probe type and imaging fluid) and contribute to AFM-inferred surface descriptors. Finally, to investigate specific bacterial cell, proteinaceous appendages in enhancing bacterial attachment to glass was investigated. P. aeruginosa PAO1 cell surface chemistry and cell attachment ability on glass substrata was examined utilizing mutants for various chromosomal encoded surface appendages, flagella, (fliM-), type IV pili (pilA -), both type IV pili and flagella (pilA- and fliM-). Attachment ability determined in macro-scale glass bead columns and batch adhesion studies to glass were larger for appendage laden WT cells compared to mutant strains. Long-range attractive adhesive forces, measured by AFM for individual cells and glass colloids (1 μm diameter), were larger for cells deficient in type IV pili. This research examined the role of nanoscopic surface features, including hydrophobicity, surface charge and roughness, in initial attachment of bacteria to substrata at the macro and nanoscale.