Type of Entry:
Inquiry Lab with field experience

Target Audience:
9-12 biology, environmental science, AP biology

Class time:
One class period to prepare, pour and label petri dishes.  One class period to collect samples.  One week  to make observations on a daily basis.

In order to do this lab the following items listed below are required.

• Petri dishes containing a gel made from agar and water (no added nutrients). Agar prep is 20 grams of agar/1 liter of distilled water.
• Containers and tools to collect the soil samples. Plastic bags to retain moisture work well
• Soil samples from different microenvironments.
• Sterile swabs and/or inoculating loops.
• Plastic wrap/parafilm- to prevent agar plates from drying out
• A culture of a suitable food bacterium, Enterobacter aerogenes.
• microscope and/or steroscope
• (optional equipment)  flex cam and TV monitor or computer hook up, digital camera

The following microenvironments are some possibilities to explore.

1. Sand (control)
2. Decayed log
3. Edge of a water source
4. Pine needle dead fall
5. Decomposing animal
6. Live tree knee.
7. Deciduous leaf dead fall
8. Middle/bottom of a water source
9. Clay soil
10. Loamy soil
11. Dry area
12. Soil moist from a human source
13. Soil naturally moist

1. If more decomposing material is present in a microenvironment, then more bacteria will  be present and consequently more amoeba.
2. If more water is present in the microenvironment, then there will be more ameoba.
3. If the source of the water is different, then the number of amoeba will vary.

• Use aseptic techniques including correct streaking procedures
• Dispose of contaminated equipment correctly
• Use an "awareness square"

Notes and Helpful Links:
Enterobacter aerogenes: Gram negative rods 0.5 to 0.8 by -1.0 to 2.0 um occuring singly.  Motile colonies  are thick, white, moist, round, smooth, entire.  Metabolism fermentative. Facultative anaerobes. Acid and gas produced from most carbohydrates, including glucose and lactose. Gelatin is slowly liquefied by most strains. Indole is usually not produced.  Citrate and acetate can be used as sole carbon source. The Voges Proskaur test is usually positive; Catalase positive; oxidase negative. Source found in the feces of man and other animals, sewage, soil, water, and dairy.

"Awareness Square" refers to using a towel soaked in antiseptic solution, such as lysol, designating the work area.

• Aseptic technique
• Autoclave use
• Amoeba source 1
• Fungi source 1
• Fungi source 2
• Nematode source 1
• Nematode source 2

Back to main page