Build a biofilm reactor
Biofilms can be produced in the laboratory using an apparatus that can be built for only a couple of dollars per unit.
Materials:
- a plastic refrigerator container
- a minature pump (Edmund Scientific J50,345)
- A 1.5 volt power source (battery or transformer)
- some plastic tubing
- bathroom or aquarium sealant
Constructing the reactor:
- Solder wires to the pump and run these out through a small hole near top of the refrigerator container
- Attach wires to the battery holder and insert two AA batteries
- Drill a hole near the base and top of the refrigerator container as shown
- Pass tubing through both holes
- Connect the lower end to the pump
- Cover the motor with a shield made of acetate glued to the side of the container
- Glue a second piece of acetate to the top edge in such a way that the stream of liquid issuing from the pump will strike the acetate and spread over the frame holding the microscope slides
- Establish culture from a non-pathogenic source in the base of the box
- Place 5-6 clean slides in a frame made from the spine of a report binder (see below).
- Place the slides in a slanted position under the trough in the top of the refrigerator container.
- Turn on the pump
- Within a few days a complex biofilm will have formed on the slides
- Slides can be examined all at once or removed individually to be replaced by clean slides to continue gathering samples
Multiple slide holder
Those pesky spines that come attached to report folders can finally find a practical use as a slide holding frame which will accomodate 5 or 6 slides.
- cut the report holder spine in half. This yields two pieces 5.5 inches long.
- notch the inside corners of the spine halves to facilitate the insertion of the slides
- clean slides in acid alcohol and load each slide into the clasping edge of the report holder spine (see diagram).
- hold the frame together with rubber bands.
- these slide frames can be used in the bioreactor as described above or sited in some natural water way to collect "natural" biofilms.
Applications:
Students can measure the effects of:
- flow rate
- substrate type
- substrate concentration
- incubation temperature
- direction of flow on cell orientation (flow vs. stationary)
Suggestions for biofilm generating cultures:
Be sure to use cultures which do not contain pathogens, for example:
- Hay infusion
- Pepper corn infusions
- Water from the classroom aquarium
- Water and sediment from an acid mine damaged stream