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This image shows a biofilm flow cell system designed to study biofilms growing under a wide range of fluid shears. The biofilms growing in the square glass tubing flow cells (available from Friedrich & Dimmock) can be monitored
in situ non-destructively. Usually the flow in one flow cell is maintained at 1 m/s (turbulent) while flow in the other is maintained at 0.03 m/s (laminar). Flows as high as 3 m/s can be achieved in these flow cells. In addition to this type of flow cell, we also use commercially available flow cells produced by BioSurface Technologies to image biofilms growing
in vitro. These flow cells, because of their thin observation windows, are particularly useful to observe initial attachment events with high power, oil immersion, objectives. However, they are generally restricted to laminar or creep flows. They can also be fitted with coupons of various materials, but work best with highly reflective materials such as polished metals.
Rougher materials usually require some kind of fluorescent staining. Remember, for coupons made from opaque materials,
use a microscope with either reflected or fluorescence capabilities.
Other Configurations
There are a number of flow cell system configurations depending on the particular experimental design. The simplest flow system is a
"once-through" system in which sterile nutrients are pumped through the flow cell into a waste reservoir. These systems are usually restricted to low flows by the time and expense of media preparation. To achieve higher flows rates I use a
recirculating system in which media is pumped into a mixing chamber and then recirculated through the flow cells. In this case, the flow velocity in the flow cells is independent of the nutrient supply flow rate and high shears can be obtained. However, in these systems detached cells can recirculate and possibly reattach. Also, waste products can build up in the system. The concentration of waste products will depend on the hydraulic residence time (the amount of time a volume of fluid stays in the flow cell system until it is washed out). Planktonic (fee floating) growing cells can be removed from the system by setting the dilution rate (volume of the flow system / flow rate of the influent medium) greater than the maximum growth rate of the organisms. This is termed "wash-out" and occurs because planktonic cells are washed-out of the system before they can divide. In this case it can be assumed that any suspended biomass was detached from the biofilm. For a flow cell of constant volume the dilution rate can be controlled by increasing or decreasing the nutrient supply flow rate. Ideally, the system should be able to be steam sterilized while fully assembled but often components such as pump heads, flow meters and pressure drop meters require chemical sterilization.
Biofilm Reactor System Schematic
References
Hall-Stoodley, L., Rayner, J.C., Stoodley, P., and Lappin-Scott, H.M. 1999. Establishment of experimental biofilms using the modified Robbins device and flow cells. In: Methods in biotechnology Vol. 12: Environmental monitoring of bacteria, pp.307-319. ed. Edwards, C. Humana Press, Totowa, NJ.
Stoodley, P., Dodds, I., Boyle, J.D., and Lappin-Scott, H.M. 1999. Influence of hydrodynamics and nutrients on biofilm structure. J. Appl. Microbiol. 85:19S-28S.
Stoodley, P., Lewandowski, Z., Boyle, J.D., and Lappin-Scott, H.M. 1999. Structural deformation of bacterial biofilms caused by short term fluctuations in flow velocity: an in-situ demonstration of biofilm viscoelasticity. Biotech. Bioeng. 65:83-92.
Stoodley, P., Hall-Stoodley, L., and Lappin-Scott, H.M. 2001. Detachment, surface migration and other dynamic behavior in bacterial biofilms revealed by digital time-lapse imaging. Methods
Enzymol. 337:306-319.
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