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105th General Meeting of the American Society for Microbiology
June 5-9, 2005, Atlanta, Georgia
For more information on any presentation at the 105th General Meeting of the ASM contact Jim Sliwa, ASM Office of Communications at jsliwa@asmusa.org

      An innovative method to improve sites that are susceptible to earthquake damage has been tested. This work used naturally occurring bacteria to strengthen saturated soils. A 15% to 87% increase in soil strength, over baseline, was achieved following the addition of biofilm-forming bacteria. These bacteria could be introduced to an earthquake-susceptible site using natural ground water flow.
      This cross-disciplinary project involved two undergraduate students, one majoring in Civil Engineering and one in Biochemistry. The work, funded by the National Science Foundation, was performed at Lafayette College in Easton PA. The results of this work are being presented at the General Meeting of the American Society for Microbiology in Atlanta, GA, June 6, 2005.
      This laboratory-based research project began with the design and manufacture of a box model. The box model allowed the simulation of groundwater flow and had multiple ports in the sides of the box to sample bacteria. Soil strength was measured using a vane shear, an instrument that measures torque resistance and correlates the measured resistance to shear strength. Flavobacterium johnsoniae UW101, a non-pathogenic, naturally occurring, low-nutrient requiring, biofilm-forming bacterium, was chosen for this research.
      Biofilms are communities of organisms that attach to, and can cover, a solid, submerged object. A biofilm may be the predominant lifestyle for bacteria. We tested for the presence of a biofilm by staining core samples with SYTO-9 and Alexa Fluor 633 and viewing the stained sample with a confocal microscope. We found that F. johnsoniae UW101 is capable of forming a biofilm on the sand inside the tank.
      Two separate tests were performed – one static (no flow) and one with gradient flow through the tank. The static test – the tank was filled with a liquid culture of bacteria and the sand was added to the tank – was done to ensure an even distribution of bacteria prior to strength testing. Under these conditions, a strength increase of 48% to 87% was measured. The other test involved adding sand to the clean dry tank and then introducing bacteria upstream of the sand. Gradient flow (upstream to downstream) was used to simulate ground water flow. After one week the downstream side was tested for the presence of bacteria and the same number of bacteria were found on the downstream as well as upstream side of the tank. Under these conditions a strength increase of 15% to 36% was measured.
      This work demonstrates a new method to strengthen saturated sand. While other means of remediation exist, most run the risk of damaging existing buildings. This method would use natural ground water flow to add biofilm-forming bacteria to an earthquake-susceptible site. While biofilms typically are thought of as a nuisance to engineers, this may be an area where biofilms are an advantage.

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EMBARGOED UNTIL: Monday, June 6, 9:00 a.m. EDT
(Session 38, Paper I-009)
Laurie Caslake
Lafayette College
Easton, PA, United States
Phone: 610-330-5462
caslakel@lafayette.edu