Activitiy 3: Nematode-trapping and mycorrhizal fungi


Activity 3: Nematode-trapping fungi; mycorrhizal fungi


Nematode-trapping fungi

This exercise will look at two different fungi that have evolved special methods for trapping nematodes.  The first we are already familiar with. 


•Pleurotus ostreatus has evolved a method of acquiring nutrition under poor nutrient conditions.  This fungus can develop secretory processes that exude a toxin that paralyzes nematodes.  The worms are then colonized by the fungus, which benefits from the additional food source.


 •Arthrobotrys is a fungal genus that has evolved the ability to trap nematodes via constricting rings.  Nematodes crawl across the surface of the hyphae and into the loops of the fungus.  In less than a second, the loop constricts, trapping the nematode and soon colonizing it with hyphae.


1) Collect a petri dish of both P. ostreatus and Arthrobotrys and examine under a microscope.  Some of these plates were fed nematodes the night before.  Some you should feed nematodes to directly and see what results.

-Can you see the sectretory processes and/or toxin droplets?

-Can you see the loops?

-Can you see any reproductive structures on Arthrobotrys?

-Can you see the nematodes in the Arthrobotrys culture?  Free or captured?

-What happens to the nematodes in the P. ostreatus culture?



•P. ostreatus was cultured on an agar and water medium.  It is essentially the same as the MEA medium but without the ME (Malt-extract).

•Arthrobotrys was cultured on MEA.  The initial culture was obtained by Connecticut Valley Biological Supply Company.

•Nematodes were also obtained by CVB.  More cultures can be grown on Potato Agar.



Mycorrhizal fungi

These fungi are important because they form mutualisms with the roots of plants.  nearly 70-80% of all plants have symbiotic relationship with one or many mycorrhizal fungi.  In the following slides, the fungi are stained red so they can be easily distinguished from the green root cells.


Observe these slides under the microscopes on the back counter.


Endomycorrhizal roots cross section - Notice the abundance of hyphae within the cells of the root cross section.  This is arbuscular mycorrhizae.  The arbuscules are not evident in these slides due to processing, but you can easily see that the cells of the root cortex are inundated with mycorrhizal fungi.


Ectomycorrhizal roots cross section - These fungi form a sheath over the root as can be seen by the abundance of hyphae around the root itself.  It also penetrates the cortex of the roots, but does not penetrate the cells with arbuscules.  It merely permeates the space between the cell walls.  This is why so many of the cell walls in the outer cortex of the root appear red.  That’s the hyphae.


These slides were obtained by Ward's Natural Science Establishment, Inc.