Worm Hunt: Isolating Soil Nematodes from Your Backyard
AbstractDo you know what is living in your backyard? How about at the playground, or in your compost pile? Nematodes, also called roundworms, are the most abundant animal on Earth and they might be living in any of these places. In this science project you'll isolate nematodes from several soil samples to discover the best nematode habitats.
This project was adapted from: Barrière, A. and Fé lix, M.-A. Isolation of C. elegans and related nematodes (July 17, 2006), WormBook, ed. The C. elegans Research Community, WormBook, doi/10.1895/wormbook.1.115.1, http://www.wormbook.org. Retrieved February 29, 2008 from http://www.wormbook.org/chapters/www_nematodeisolation/nematodeisolation.html
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In this science project you'll isolate nematodes from a variety of soil samples to determine which types of soil are the best nematode habitats.
Nematodes, also called roundworms, are the most abundant multicellular animals on Earth. There are more than 15,000 identified species of nematodes, and scientists are still discovering new ones! Most nematodes are 1-5 millimeters (mm) long, but scientists have identified a few very long nematodes, too, like Placentonema gigantisma, an 8-meter-long nematode found in the placenta of a sperm whale. All nematodes have fairly simple body plans. These animals are tube-like in shape; have an outer body wall, called a cuticle; and a digestive track that runs most of the body length. Because of this relatively simple body plan, nematodes are sometimes described as "a tube inside a tube." Here are two very different nematodes in Figure 1.
Figure 1.a. Caenorhabditis elegans is a bacterivorous soil nematode that is approximately 1 mm long as an adult. (WormBook, 2006.)
Figure 1.b. Ascaris lumbriocoides is a parasitic nematode that can live in the human intestine and grow to be 15-30 centimeters (cm) long. (CDC.)
Despite a simple body plan, nematodes are complex animals. Scientific research using a variety of nematodes has been important in understanding ecology, medicine, and basic biology. One of the most well-studied nematodes is Caenorhabditis elegans. C. elegans are approximately 1 mm long, are found in soils all over the world, and feed on bacteria. These small worms are used to study a variety of biological phenomena. In fact, research using C. elegans has been so important that several scientists who used C. elegans in their experiments have won the Nobel Prize!
Where can you find nematodes? Just about everywhere. They're residents of many different habitats, including soil, plants, freshwater, and saltwater. Some nematodes are even parasitic, meaning they live, grow, and reproduce inside other organisms at the expense of their host's health. Such a wide range of habitats also means that among the various nematode species, there is a lot of diversity in what they eat. Soil nematodes include bacterivores (bacteria eaters), fungivores (fungus eaters), algivores (algae eaters), and herbivores (plant eaters). In this science project, you will isolate bacterivorous nematodes from soil samples in your own backyard, or from any other local soil areas you choose.
Terms and Concepts
- Body plan
- Caenorhabditis elegans
- Where can you find nematodes and what do they look like?
- What kinds of food do nematodes eat?
- Would you expect to find nematodes in your backyard? If so, what species of nematodes?
One of the best places to start your bibliographic research is an encyclopedia. Try looking under Nematoda, which is the phylum name for nematodes. Other good resources include:
- Parker, Steve. Nematodes, Leeches & Other Worms. Minneapolis, MN: Compass Point Books, 2006.
- University of California Museum of Paleontology Community. (n.d.). Introduction to the Nematoda. University of California Museum of Paleontology. Retrieved February 29, 2008.
- McSorley, Robert. (2007). Featured Creatures: Phylum Nematoda. University of Florida. Retrieved July 31, 2013.
- Neutralizing Bacteria Kit, available from our partner
Home Science Tools. Needed from the kit:
- Nutrient agar plates (9)
- E. coli culture, freeze dried and ready to reconstitute
- Nutrient agar plates (three for every soil location, with a minimum of 9 plates)
- Sterile cotton swabs
- Nitrile gloves
- You will also need to gather these items, not included in the kit:
- Bunsen burner or, if not available, a candle
- Magnifying glass, available from our partner Home Science Tools
- Tablespoon measuring spoon
- Soil samples (minimum of three locations, each with a different type of soil); here are some ideas of different sample soils to test:
- Sandy soil
- Garden soil
- Playground dirt
- Soil underneath a fruit tree
- Plastic baggies (3 for each soil sample)
- Incubator or, if not available, a warm dry location
- Permanent marker
- Clock or timer
- Lab notebook
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For health and safety reasons, science fairs regulate what kinds of biological materials can be used in science fair projects. You should check with your science fair's Scientific Review Committee before starting this experiment to make sure your science fair project complies with all local rules. Many science fairs follow Intel® International Science and Engineering Fair (ISEF) regulations. For more information, visit these Science Buddies pages: Project Involving Potentially Hazardous Biological Agents and Scientific Review Committee. You can also visit the webpage ISEF Rules & Guidelines directly.
This science fair project involves the use of the bacteria E. coli. While E. coli is not considered a biohazardous or dangerous bacteria, it is important to always properly clean and dispose of bacteria and supplies that come in contact with it. See the Bacterial Safety guidelines below for more details on how to handle bacterial cleanup and waste.
Prepare the Bacterial Plates
- Take out your E. coli culture and follow the instructions in the kit to reconstitute the dried bacteria. Wait 5 minutes after reconstituting, then mix the gently shake to mix the bacterial suspension one more time.
- Put 2 drops E. coli culture on the surface of an agar plate. Try to put the culture in the center of the plate.
- Use a sterile cotton swab to spread the bacteria around the entire surface of the agar plate as shown in Figure 2.
- Streak a vertical line across the surface of the agar plate.
- Starting from the top of the plate and moving downward, spread the streak back and forth (to the left and right), from edge to edge. Stop when you reach the bottom of the plate.
- Rotate the plate 60 degrees clockwise and repeat step ii.
- Rotate the plate another 60 degrees clockwise and repeat step ii.
- This approach will make sure the bacteria are spread evenly across the plate.
- Tip: Try not to pierce, or rip, the surface of the agar.
- Put the lid on the plate as soon as you are done.
- Repeat for the rest of the agar plates.
Four images show the correct method of spreading bacteria on an agar plate. First a vertical line of bacteria is streaked across the length of the plate. Then bacteria is spread left to right across the plate moving from the top of the plate towards the bottom. The plate is then rotated 60 degrees clockwise and bacteria is again spread from left to right moving from the top of the plate towards the bottom. Finally the third step is repeated and the plate is rotated another 60 degrees clockwise and bacteria spread from left to right moving from the top of the plate towards the bottom.
Figure 2. On each agar plate, streak the bacteria by first making a vertical line, then spreading this left to right (and top to bottom), rotating the plate 60 degrees clockwise and again spreading the bacteria left to right (and top to bottom), and then rotating the plate another 60 degrees clockwise and spreading the bacteria again. Note: The bacteria should all be the same color on your plates. Color has been added in this diagram to help clarify the procedure.
- Incubate the plates, with their lids on, for 72 hours at room temperature for the E. coli lawn to grow. Avoid keeping the plates in direct sunlight or they will dry out. Alternatively, if you have access to an incubator that will maintain a temperature of 37°C, the E. coli lawn will grow within 24 hours if the plates are placed in there.
- Using a tablespoon, collect 2 Tablespoons (Tbsp.) each of several soil samples, keeping them all separate in plastic baggies. Using a permanent marker, label each baggie with respect to the type of soil sample and replicate. For example, Playground A. Try diverse locations and/or soil types. Make sure to collect the samples in triplicates so that you have replicates for your experiment. For example, if you collect compost soil and playground dirt, you should have compost soil samples A, B, and C, as well as playground dirt samples A, B, and C. At least one of your samples should be a nutrient-rich soil, like compost or fertile garden soil.
- Once you are back inside, slightly dampen each soil sample with ¼ teaspoon of water, while the soil is still in the baggies.
Using a permanent marker, label each agar plate with respect to the type of soil sample and replicate. For example,
Playground B. (Note: Always label the bottom or sides of agar plates, rather than the lids. That way you will not get your samples mixed up if you take off the lids of more than one plate at once.) Distribute the soil samples in a ring around the E. coli lawns, as shown in Figure 2 below. Each sample should go on a separate agar plate.
Figure 3. In this nematode isolation setup, the damp soil is placed around the E. coli lawn. If there are any nematodes in the soil sample, they will crawl toward the E. coli. (Wormbook, 2007.)
- After 30 minutes, examine the plates using the magnifying glass. Which plates have nematodes on the E. coli lawn? How many nematodes do you see per plate? Using your lab notebook, record your findings in a data table like this:
|Soil Sample||Replicate||# of Nematodes|
- From your three replicates, calculate the average number of nematodes per soil sample. Advanced students may want to calculate the standard deviation. Which types of soil or soil locations have larger populations of nematodes?
Bacteria are all around us in our daily lives and the vast majority of them are not harmful. However, for maximum safety, all bacterial cultures should always be treated as potential hazards. This means that proper handling, cleanup, and disposal are necessary. Below are a few important safety reminders.
- Keep your nose and mouth away from tubes, pipettes, or other tools that come in contact with bacterial cultures, in order to avoid ingesting or inhaling any bacteria.
- Make sure to wash your hands thoroughly after handling bacteria.
- Proper Disposal of Bacterial Cultures
- Bacterial cultures, plates, and disposables that are used to manipulate the bacteria should be soaked in a 10% bleach solution (1 part bleach to 9 parts water) for 1–2 hours.
- Use caution when handling the bleach, as it can ruin your clothes if spilled, and any disinfectant can be harmful if splashed in your eyes.
- After bleach treatment is completed, these items can be placed in your normal household garbage.
- Cleaning Your Work Area
- At the end of your experiment, use a disinfectant, such as 70% ethanol, a 10% bleach solution, or a commercial antibacterial kitchen/bath cleaning solution, to thoroughly clean any surfaces you have used.
- Be aware of the possible hazards of disinfectants and use them carefully.
Ask an Expert
- Does soil depth have an effect on nematode abundance? Compare the number of worms isolated from different soil depths. Remember to change only one variable at a time!
- Do different species of nematodes live in different soils? Try classifying the nematodes you find in each soil sample based on physical traits. You'll need a microscope to see the worms in more detail. You'll also need to research different species of soil nematodes.
- Not all soil nematodes are bacterivorous. Some species are plant parasites and others consume fungi. Design an experiment to examine plant- or fungi-eating nematodes.
- Soil is only one of the many habitats nematodes are found in. Design an experiment to examine marine or freshwater nematodes.
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