Submitted to: Water Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/9/2009
Publication Date: 2/1/2010
Publication URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2288.pdf
Citation: Kim, H., Walker, S., Bradford, S.A. 2010. Macromolecule Mediated Transport and Retention of Escherichia coli O157:H7 in Saturated Porous Media. Water Research. 44(4):1082-1093. Interpretive Summary: Escherichia coli O157:H7 has caused food and water-borne disease outbreaks in the United States. The objective of this study was to study the influence of macromolecules on the cell surface on their transport and retention in sand. Two major findings were observed: (i) cell retention was significantly influenced by the surface macromolecules; and (ii) interactions associated with macromolecules had a strong relationship with the solution ionic strength. This study helps us to better understand cell–cell/cell–sand interactions associated with macromolecules on the cell surface and provides insight on the removal of E. coli O157:H7 in sand. This information will be use to scientists, engineers, and regulators concerned with the fate of E. coli O157:H7 in soil and groundwater environments.
Technical Abstract: The role of extracellular macromolecules on Escherichia coli O157:H7 transport and retention was investigated in saturated porous media. To compare the relative transport and retention of E. coli cells that are macromolecule rich and deficient, macromolecules were partially cleaved using a proteolytic enzyme. Characterization of bacterial cell surfaces, cell aggregation, and experiments in a packed sand column were conducted over a range of ionic strength (IS). The results showed that macromolecule-related interactions contribute to retention of E. coli O157:H7 and are strongly linked to solution IS. Under low IS conditions (IS < 0.1 mM), partial removal of the macromolecules resulted in a more negative electrophoretic mobility of cells and created more unfavorable conditions for cell–quartz and cell–cell interactions as suggested by Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profiles and cell aggregation kinetics. Consequently, less retention was observed for enzyme treated cells in the corresponding column experiments. In addition, a time-dependent deposition process (i.e., ripening) was observed for untreated cells, but not for treated cells, supporting the fact that the macromolecules enhanced cell–cell interactions. Additional column experiments for untreated cells under favorable conditions (IS < 1 mM) showed that a significant amount of the cells were reversibly retained in the column, which contradicts predictions of DLVO theory. Furthermore, a non-monotonic cell retention profile was observed under favorable attachment conditions. These observations indicated that the presence of macromolecules hindered irreversible interactions between the cells and the quartz surface.