Superfund Research Program

Bacterial Transport in Saturated, Unsaturated, and Air- Sparged Porous Media

Project Leader: Bruce E. Logan (Pennsylvania State University)
Grant Number: P42ES004940
Funding Period: 1995 - 2000

Project-Specific Links

Final Progress Reports

Year:   1999 

Project investigators concluded bacterial transport and adhesion studies. Column experiments demonstrated that previously deposited bacteria could block subsequent deposition of bacteria and that surfaces were blocked at very low soil surface coverage (<3-5%). Several papers were published summarizing other work related to the effects of dispersion, unsaturated flow, and non-aqueous phase liquids on bacterial transport. Laboratory work concentrated on development of procedures to study bacteria using atomic force microscopy (AFM) in order to determine the specific cell properties that determine bacterial adhesion and better understand the effects of chemicals (such as surfactants) and low IS water on cell-surface interactions observed in column studies. Researchers developed a new technique to anchor bacteria to glass slides for AFM imaging (crosslinking carboxyl groups on the bacterial surfaces with amine groups that had been coupled to glass slides). Topographic images, phase images, traces of surface topography, and analyses of surface roughness were performed on all samples.

Bacteria (Burkholderia cepacia G4 and Pseudomonas stutzeri KC) were exposed to Tween 20, heparin, disodium tetraborate, sodium pyrophosphate, low ionic strength (IS) water, lysozyme/ethylenediaminetetraacetic acid (EDTA), and 3-(4-morpholino)propane sulfonic acid sodium salt (MOPS) buffer (as a control) and the surface topography of the cells was examined after exposure to each chemical. All of the treatment chemicals except disodium tetraborate caused higher height variations to be measured for G4 and KC. Disodium tetraborate flattened the cells and therefore, resulted in slightly lower or equal average surface heights compared to controls (MOPS buffer). Heights could be correlated with the qualitative shapes of the cells. Lysozyme/EDTA, sodium pyrophosphate, and disodium tetraborate produced the most damage to cellular morphology, as observed by topographic images and surface traces, and decreased cellular viability. AFM force measurements were used to demonstrate that bacterial surface polymers dominate cell-surface interactions and that the effects of ionic strength and pH on these polymers control observable adhesion properties of these cells.