Slime Molds - not really molds -- but definitely slimy, weird, and wonderful!

Sometimes specimens come to me.  Dana See, one of our lab techs here at Eastfield, who loves all creatures, great and small, has begun growing slime molds for fun.

They actually make great pets.  They make no noise, have no smell, eat very little, and don't have to be walked or trained to use a cat box.

Here is a photo of one of Dana's slime molds - Physarum polycephalum.  It is growing on plain agar - no nutrients.  The agar provides a moist surface for the slime mold to grow on.  The yellow blobs are rolled oats.  The slime mold crawls out to the oats, covers them, and digests them.

So what exactly is a slime mold?  Turns out that is a pretty good question.  They crawl around but are not animals.  They were classified as fungi originally, probably because they are non-photosynthetic, use external digestion, and form spores in fruiting bodies, but genetic analysis shows they aren't related to fungi - at all. 

The type of slime mold that Dana is growing is essentially a syncytium, or supercell - a cytoplasmic mass with multiple nuclei.  It moves via cytoplasmic streaming, very much like an amoeba, but on a much larger scale.  Here are a couple of links if you are interested in finding out a little more.

http://www.ucmp.berkeley.edu/protista/slimemolds.html

http://en.wikipedia.org/wiki/Slime_mold

Of course my job is to let you see what these guys look like in my microscopes.

The instructor's microscopes in each of our labs are equipped with digital cameras.  Below is a short YouTube video I recorded of cytoplasmic streaming in Polycephalum.  



Reproduction in slime molds is also a little strange.  You can cut a piece of live slime mold off and put it in a new petri dish with agar, or on a damp piece of paper towel, give it a few oats, and it will thrive.  Keep it moist and fed and it will crawl out of the petri dish!

You can let the slime mold dry out on a piece of filter paper and it will go dormant.  Add water and oats and it will become active again. The dried out slime mold, called a sclerotium, is how I used to order slime molds for my classes.  They will stay viable for long periods of time in this dried out stage.

This slime mold (the yellow coloring) has produced dark fruiting bodies.  This slime mold culture was maintained on damp paper towel.

Let's take a closer look at some fruiting bodies using a dissecting scope. Several of these images were made by a student - Brandon Cullen.  Interestingly, it was his first time to use this particular microscope. He has a real talent for imaging.

This slime mold was growing on an agar plate. The yellow, snotty looking stuff is the body of the slime mold.  The dark structures on stalks above the surface are fruiting bodies.

In this image you can see that the older parts of the fruiting bodies are drying out and ready to release spores.

In this image Brandon was focusing in on the attachment between the stalk and the sac that contains the spores, the sporangium. Also note the white spots on the spore sac.  More detail coming up on those with the electron microscope 

These next three images, also taken by Brandon, and are truly exceptional.

The following images were taken with the Hitachi S3400-N Scanning Electron Microscope.

[49x]
A fruiting body on its stalk.  The base of the stalk is coming from the slime mold which is on an oat.  At the top left of the image you can see the fibers of the paper towel.

[67x]
In this image you can see that the sporangium has split open.  The electron microscope operates under high vacuum and really dries specimens out.  This drying probably broke open the sac.  Note the white spots on the sporangium and the fibers of the paper towel in the background.

[360x]
A close-up of the stalk of the fruiting body.  It is collapsed because of the high vacuum in the microscope.  

[100x]
Spores inside the spore sac.  

[1,800x]
Slime mold spores - some on top of the spore sac and some still in the sporangium.  Notice the white glands on the surface of the sporangium.

Spores at 3,700x magnification.  The lines across the image are and artifact of the imaging process.

[270x]
The white spots that were visible with the dissecting scope appear in two different forms - a collection of small glands and some fibrous structures.

[1,000x]

[1,390x]
To the right of the image are some individual spores.  Note the sizes.  What are the functions of the white glandular and fibrous structures?  I have no idea.

[1,500x]
There appear to be small glands all over the outside of the spore sac both singly and in clusters.

I have always enjoyed slime molds simply because they are so unusual, but until I had the opportunity to use the microscopes at the Microscopy Lab here at Eastfield College I had never taken a really close look at them.  They are even more weird that I expected - which makes me like them even more.

I wasn't kidding about having slime molds for pets.  If you want to grow your own here is a link to a kit from Carolina Biological.

http://www.carolina.com/slime-molds/physarum-polycephalum-sclerotium-living-box/156190.pr?catId=&mCat=&sCat=&ssCat=&question=slime+mold+cultures

A reminder that all images are covered by a Creative Commons License.  You may download, modify, reproduce,transmit, or use any of these images as long as you give attribution to Eastfield College, Mesquite, TX.  None of these images my be sold.

Murry Gans
Microscopy Lab Coordinator
Eastfield College