Faculty Advisor

John Bergendahl

Faculty Advisor

Terri A. Camesano


Studying the interactions between bacteria and soil colloidal particles in the environment is important for bioaugmentation purposes. Different factors affect the transport of the bacteria in porous media. For example, the soil type, the ionic strength of the substrate, and biological properties, such as the bacterial cell motility. Since organic materials are present in almost all subsurface media, the presence of natural organic matter (NOM) is considered an important factor influencing bacterial transport in porous media. In this work, a model system was developed to examine the interactions between natural colloidal particles and environmental bacteria using Atomic Force Microscopy (AFM). The natural colloids in the environment were modeled by a surface film of adsorbed NOM onto spherical SiO2 particles. Poly(methacrylic acid) (PMA), a simple linear polyelectrolyte, was used to mimic NOM since both are dominated by carboxylic acid functional groups. Soil Humic Acid (SHA) and Suwannee River Humic Acid (SRHA), two acidic polyelectrolytes, were used in further experiments to represent more complicated NOM. A smooth strain of Pseudomonas aeruginosa (PAO1) that coexpresses A-band and B-band polysaccharides, and its rough mutant (AK1401) that only expresses the A-band polysaccharides, were chosen to represent environmental bacteria. The model system was characterized through analysis of the measured forces between the chemically-modified colloidal probes and the bacterial cells. Interestingly, we found that PMA was not a good model for the more complex NOM substances. Differences were also observed in how each bacterium interacted with the three forms of NOM. For example, P. aeruginosa PAO1 had the highest adhesion with both complex forms of NOM, while P. aeruginosa AK1401 had the lowest adhesion with the complex forms of NOM. Since the lipopolysaccharide (LPS) structure is the only difference between the two strains, we attribute the different interactions to differences in LPS structure. The polymer density on the bacterial surface was found to be the most important factor in controlling the nature of the interaction forces.


Worcester Polytechnic Institute

Degree Name



Civil & Environmental Engineering

Project Type


Date Accepted





AFM, Bacterial Adhesion, Soil microbiology, Atomic force microscopy, Bacteria, Adhesion, Groundwater, Pollution, Organic water pollutants, Analysis