One of the most common model organisms used in laboratories is the nematode: Caenorhabditis elegans. This nematode species is great for studying toxicity responses, modeling human disease, studying aging and much more. They are simple to take care of, have a lifespan of 3.5 days, which makes them a great addition to any laboratory! In order to start culturing C. elegans, you’ll need a few things like nematode growth medium (NGM), the bacteria they feed on, and the worms themselves.
Once your NGM plates are poured and solidified, you’re only a few short steps away from starting the culturing process. In order to make the NGM plates a habitable environment for the worms, a liquid culture of OP50 has to be added to the plates. OP50 is a strain of E. coli that the worms feed on, it is the ideal strain for this since OP50 E. coli exhibits limited growth on NGM plates (unlike E. coli’s rapid growth and colony formation on plates containing LB Agar). When you add the OP50 it is best to let the plates absorb the culture for at least 2 hours to overnight. Once the plates have been seeded with OP50, then you can begin chunking the worms!
Chunking C. elegans
“Chunking” is a term used to describe the method of taking a chunk out of the existing agar that the worms are growing on and transferring it to a fresh and recently seeded NGM plate. This is done usually with a sterile inoculation loop. When chunking the worms, I like to look for a well populated area of the plate and cut out a 1×1 centimeter square using the loop. Then carefully transfer the chunk to the new plate, but place it upside down so that the worms are able to transfer themselves to the fresh plate. When you’re new to taking care of C. elegans you will want to use your microscope before chunking to make sure that there are enough worms on your plate to chunk, and establish where they are beforehand to make the process easier.
Keeping the Worms Alive
After the worms have been chunked to a new plate, they’ll need to be fed regularly to continue living and reproducing. To do this, take about 150-200 microliters of OP50 media and add it to the plate. Be careful not to invert the plate until the OP50 has absorbed into the agar, as the worms can come loose and be displaced onto the lid. It’s good practice to feed them 1-3 times per week, and to chunk them about every 10-14 days.
Avoiding Common Pitfalls
If it looks like there are no worms on your plate, they may just be hungry and hiding in the NGM. You can feed and observe them to see if that helps the worms to come out of the agar, but I’ve found that chunking them onto a freshly seeded NGM plate helps them come out of hiding the best! As long as the agar is not dry, the worms can be re-chunked and will replicate. C. elegans also like to be kept at room temperature, so when you are getting set up make sure the location you plan to keep them doesn’t get too hot or too cold. If you are handling multiple mutant strains along with a wild-type strain, make sure you are very careful to replace the inoculating loop each time you chunk if you are using disposable ones. Another way to avoid cross-contamination is to wipe down your work surface with 70% ethanol before handling the worms, between chunking each species, and at the end when you are finished.
C. elegans are a great model organism, and fairly easy to keep up with. We offer kits for you and your students to explore the behavior and characteristics of these worms, which you can check out below. We also have a helpful YouTube video about C. elegans!
Edvo-kits with C. elegans: