Science Buddies: "Ask an Expert"

I have completed the experiment "Isolating Nematodes." Even after waiting 48 hours, I didn't see any nematodes in any of the plates. Is there a place to see what I should be looking for? I have documented "0 nematodes" in my result table for all the plates at several time intervals. I did do three samples of each soil location.

Thank you for any help or advice.

Hi Jenn,
I'm sorry you had this experience. I work with worms so I'm happy to help you figure out what's happening.

Did you follow the procedure outlined here?
https://www.sciencebuddies.org/science- ... r-backyard

Here are a few suggestions for you to consider:

1. One way to increase the chances of your soil sample having more nematodes is to collect soil from an area with decaying organic material (like leaves, fruits etc.), rather than soil that appears 'clean'. Since you mentioned that you sampled multiple locations, maybe you already had some soil from such a place.

2. Are you viewing the plates through a magnifying glass or a low powered microscope? Nematodes can sometimes be viewed with the naked eye but not easily and does require a trained eye.

3. Make sure the soil that you place on the plate does not cover the bacteria. If that happens, it will be difficult to spot the worms among the soil particles, even if they are there. The bacteria should ideally be in a clear patch, near to the soil but not overlapping with it or covered. Worms are remarkably good at sensing the food source and crawling to it. Normally you should be able to see worms hanging out where the bacteria is.
Also make sure, the bacteria has grown well before you transfer the soil samples to the plate. This can be done by keeping the plate with bacteria added, in a warm location for 1-2 days. If there isn't sufficient bacterial growth, the worms won't be attracted there.

4. When you applied the bacteria to the agar plate, did you get any cracks/cuts on the surface? If so, then the little worms are likely hiding in the cracks. Worms are natural diggers but they can't easily dig the agar surface. A slightest gap in the surface however gives them an opportunity to dig and go under, and they love doing that.


Finally, here is an example image of worms look like on an agar plate, so that you know what you're looking for.
http://www.sommerlab.org/about-p-pacificus.html
Check out the second image. The bacteria here has been applied as a patch to form a 'lawn' rather than by streaking as described in the project. Both should work.

Note that nematodes crawling around on bacteria leave little trails as they go and you can often view that easily by holding the plate up to light.

Hope this helps. Please reach out again if you have additional questions.
Good Luck!
MS

Thank you for answering. I did follow the procedure exactly and used a magnifying glass to search for the nematodes.

Hi Jenn,
Thanks for clarifying. I would suggest you try the specific tips I gave you, if you have a chance. I'm pretty confident you will be able to see some worms.
Good luck,
MS

Hello!

In addition to the great advice provided by a fellow expert, if you have access to a microscope, you may want to use one to view the nematodes. Where did you collect the nematodes from? Soil nutrient content plays a large role in the presence of these organisms, so it is possible that the nematodes were not present at one or more of your sample locations depending on the type of soil. Some species of fungi are predators to nematodes, so if there was a large presence of fungi at any of your sample locations, this may be why you are not finding the nematodes.

Also, make sure to try to view the worms very soon after you place them on the agar plate, as it is extremely difficult to see them if they burrow into the agar surface. Assuming you are using a tool to move the soil with worms in it onto the agar plate, take care not to kill the worms with any tools you are using. The nematodes are also easiest to see when there are not any cracks or crevices in the agar, so try your best to be as careful as possible to keep all gel-like surfaces intact.

At what depth did you collect your soil samples? After some quick research, it seems that most nematodes are usually found at a depth of around half of 1 foot, or 6 inches deep.

Always be careful to protect you own heath when handling these organisms!

Hope this helps!
-cnoonan180