Mechanisms of bacterial adhesion to solid surfaces in aquatic systems

The fundamental mechanisms involved in the initial stages of bacterial adhesion to mineral surfaces have been systematically examined. Two deposition systems were employed: a radial stagnation point flow (RSPF) system and a packed bed column. The kinetics of cell adhesion onto a quartz surface were determined under a range of ionic strengths, systematically adjusting the bacterial type, growth phase, and nutrient conditions. The transport experiments were complimented by a range of characterization techniques which provided insight into the physical and chemical characteristics of the cell surface.; Experiments utilizing E. coli K12 strains found the distribution of charged functional groups on the lipopolysaccharides (LPS) and outer membrane of the bacteria controls the extent of interactions. It was also determined that metabolic and physiological changes occurring with culture age affect cell adhesion. Stationary phase cells were more adhesive than mid-exponential growth phase cells, which is attributed to fewer proteins and more LPS exposed on the cell surfaces at a later growth phase.; To compliment the previous work, adhesion studies were conducted with Burkholderia cepacia. Comparable adhesion kinetics were observed for the mutant (ENV435g) and wild-type (G4g) grown in the same medium; however, the rate of adhesion increased with the level of nutrient presence for both cell types. Experiments demonstrated that the extent of adhesion is dependent on a combination of physical and chemical interactions, as nutrient condition altered the size and resulting chemistry of the exposed cell surface macromolecules.; The hydrodynamics in the two deposition systems are distinct and therefore capture different adhesion mechanisms. Cells in the packed column system deposit in both secondary and primary minima, while only cells deposited in a primary minimum are enumerated in the RSPF due to the hydrodynamics in the system. As the presence of surface charge heterogeneity decreases electrostatic repulsion and increases the rate of irreversible attachment in the primary minimum, the impact of heterogeneity will be greatest on the deposition rate in the RSPF system.; This research established that no single surface molecule on the bacterium determines the extent of adhesion. Rather, the presence and distribution of charged ionic species---originating on cell surface macromolecules---determines the interaction forces involved.