ALCA Members PLC Domains Data Standards Map Plan Curriculum Assessment Strategies

Microbes of the Soil Copy

By using this proven technique, we want to isolate as many different top-soil and sub-soil microbes, within our community as possible.Without any previous study in the microbiology field, most biology students assume that microbial life would be most abundant in the prescence of air [or above ground]. That assumption would infer that the number and variety of microbes, just a few inches deep, would be reduced. Let's see how that assumption holds up in our neighborhood.

Teacher Goals

  • With the investigation of top soil and subsoil, the complexity of life should become obvious.

Required Resources

  • Material List

    1. GPS unit
    2. [x25-30] Toothpicks [sealed in a zip lock bag]
    3. Grease pencil or felt-tip pen
      Magic-Markers are not preferred, as they will make too wide a stroke.
    4. [x32] Pre-poured Slants [screw-top test tubes with nutrient agar]
      Place a peel-off label on each slant. If none is available, use a wax pencil for labeling [see Instructions #5]
      DO NOT OPEN the slants until you are ready to insert a field-sample.
    5. Notebook and pen for jotting down field-notes
    6. Small trough or digging device
    7. aluminum foil or Parafilm
    8. Bergey's MANUAL OF SYSTEMATIC BACTERIOLOGY [Pub. Williams & Wilkins]

  • Field-Data Survey Forms

    List your data in the following forms.
     

  • Microbes/Student Checklist/Performance Rubric

    This rubric may be used as a student/teacher checklist or a teacher evaluation tool. It is based on a point grading system. To calculate a percentage grade, divide the total points earned by the total points possible. Total Points Possible: 54
     

Optional Resources

  • Microscope
     

  • Science Manuals

    Try this site on the internet for help with anything found in a library.

Steps

  1. The Plot

    Use the Field Data Sheet Grid. For the 'Microbes of the Soil Activity' you will need to reduce the dimensions of the grid to a one-foot-square plot. Each area will be only three inches on a side, instead of 0.5 meters.

    The heading of each area will not change, i.e. 1A, 2A, etc.

    The choice of ground is up to the student.
     

  2. Map Area

    On the 'Field Data Sheet Grid' clearly mark North .
     

  3. GPS Unit

    With a GPS unit determine the geographical position. Place the latitude and longitude ['lat & long'] at the top of the 'Field Data Sheet Grid'.
     

  4. Digital Photo

    Take a Digital Photo of the site facing due North.
     

  5. Label the Slants

    Label sixteen screw-top test tubes: "Top Soil-1A" through "Top Soil-4D". Then label the remaining screw-top test tubes 'Sub Soil-1A' through 'Sub Soil-4D'.
     

  6. Top Soil Samples

    Take all 'top soil' samples first. Start by simply rubbing a toothpick over the soil in grid 1A. Then open the test tube marked Top Soil 1A, and with the 'exposed toothpick' gently rub only the surface of the agar.

    Note: Do Not stab the agar with the toothpick. Now with a clean fresh toothpick, repeat this step for each area.

  7. Sub Soil Samples

    Return to sample area #1. Using the digging instrument, and trying not to disturb the other areas, dig down approximately two inches. Now poke the freshly exposed soil with a clean fresh toothpick.

    Next, open test tube 'Sub Soil 1A' and spear the agar with the toothpick. In this way the gathered material will again be isolated from the atmosphere. Next tightly close the cap. Repeat this process with each of the sixteen areas.
     

  8. Incubation

    AS SOON AS POSSIBLE, replace the lids on 'top soil' specimens with aluminum foil or Parafilm.

    Keep ALL SPECIMEN test tubes in a place where the temperaure is roughly the same as the sample area. NOTE: keep the sub soil specimen in the dark.

    Allow the specimens to grow for 2-4 days.

    Chart your observations each day for each sample.
     

  9. Identification

    Using a "Bergey's Manual", identify the growing bacterial colonies in each slant. "Bergey's" will give you exact instructions on how to accomplish this. For help see 'Optional Resources #2'

    If you have been trained by your teacher in the proper processes for making microscopic slides, you may prepare some. Otherwise, that activity will be demonstrated in class by your teacher.
     

Teacher Notes

  • In preparation for this activity, place the toothpicks in baggies to reduce contamination. Be sure to instruct the students not to open or handle the toothpicks except during the actual sample taking.

  • Re-inforce the ease at which their slants can be contaminated, for example:
    1] leaving the cap off too long
    or 2] setting the cap down while taking a sample.

  • Demonstrate the technique for opening a slant or bottle while NOT setting the cap down.

  • Pour the agar into the screw-top test tubes and set them on a slant to solidify. Once the slants have set, place seventeen[x17] into a baggie. This will be enough for one team [with one extra 'just in case']. This can, and should be done, several days in advance. That way any problems can be addressed then, and you will not have to change the schedule of your lab activity.

Learner Notes

  • The most common problem seen in these types of labs is CONTAMINATION. When gathering a sample touch only one tip of the toothpick. If you acidentally touch both ends, discard that toothpick.

  • When gathering top-soil samples, once you have rubbed the 'exposed' toothpick onto the slant, you should not leave the toothpick in the tube. To do so invites contamination.
     

Mentor Notes

  • In preparation for this activity, be sure the toothpicks are in baggies to reduce contamination. Remind your child not to open or handle the toothpicks except during the actual sample taking.

  • Remind your child of the ease at which the agar-slants can be contaminated, for example:
    1] leaving the cap off too long
    or 2] setting the cap down while taking a sample.

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