Attachment of E. coli Strains to Model Environmental Particles in Streams and Stream Sediments.

Microorganisms in streams can move in a freely suspended state or by attaching to suspended sediment and organic particulates. Bacteria that are attached to particulates are more resistant to environmental stresses, including ultraviolet radiation. Bacterial attachment to particulates in aquatic environments is a dynamic process; it may be affected by bacterial properties, particle surface properties, and environmental factors. Bacterial properties include the presence or absence of flagella, the physiological growth state, cell size, hydrophobicity, the electrostatic charge at the cell surface, and the presence of outer-membrane proteins and polysaccharides. Bacterial attachment to particulates can also be affected by the properties of particulates: e.g., size, surface charge, hydrophobicity, coatings, and organic matter content. Environmental factors such ionic strength, pH, and temperature also regulate the attachment of bacterial cells to particulates in the stream. The objectives of this study were to investigate the variability in cell properties and particulate properties as well as the correlation between the attachment behavior of E. coli isolates and those properties. Seventy-eight genotypically different strains of E. coli were selected for further study from 400 strains that had been isolated from stream water and stream sediments in central Iowa. Cell properties such as hydrophobicity, surface acidity, zeta potential, size, and the composition of extracellular polymeric substances were measured for these strains. Three model particulates were also investigated to represent typical suspended stream sediments to which bacteria might be attached: Ca- montomorillonite, ferrihydrite, and ground corn stover. Properties such as size, surface area, and organic carbon content were measured for each model particulate. Finally, we conducted studies at environmentally relevant pH and ionic strength conditions to assess which bacterial and particulate properties had the greatest impact on rapid attachment of the selected E. coli strains. The results of this study will be helpful in modeling bacterial transport and fate in the environment.