Und Zis is How We Culture Cellular Schleim Molds in Germany

To celebrate Friday, here’s the best video I’ve ever seen illustrating cellular slime molds, the borg-like creatures that start out as individual amoebae in the soil but then aggregate into a slug that roves around a bit before rearing up into a sporangium, or spore capsule. This particular species seems to be the cellular slime mole lab rat, Dictyostelium discoideum (dik’-tee-o-steel’-ee-um dis-koid’-ee-um). Notice how (apparently) easy it is to find these guys in the soil!

Video is, unfortunately, in German. If you don’t speak German, consider making up your own (PG) translations to key scenes and sharing them with us in the comments! : )

In the beginning you see the free-living amoebae (I think) happily wandering about on their own with some fungal filaments (called hyphae, high’-fee) growing at the top of the screen. Then the ameobae start aggregating — crowding after each other like sports fans filling a stadium. The species uses a famous signaling molecule called cyclic AMP (cAMP) to coordinate their union, and it passes through the swarms in pulsing, spiraling waves noticeable at about 1:35. If I’m using my extremely poor knowledge of German correctly, the narrator is nothing that hundreds of thousands of amoebae join together in the process. They do not fuse membranes; they retain their cellular identity.

Notice that some amoebae get left behind or lost in the process. At 2:47 you can actually see some break out of line and go back to being  little amoebae at the very tail end. After the spiraling and pulsating business is done, the mass stretches into a slug and crawls off. At some point between forming the slug (also called a grex) and making the sporangium (the house where spores are made), the amoebae get it on and mix some genes.

When the slug decides conditions are perfect, it stops, puddles up, and then stretches skyward. The lucky amoebae who will become spores riding up the stalk like an elevator. Those stalk cells get the rotten end of the deal — they must sacrifice themselves to ensure their comrades can reproduce. This little detail has led scientists to study these organisms in order to better understand altruism and cheating in nature. What they’ve found is that, as ever, things are not always as they seem. Some would-be stalk cells indeed give their lives, but others buck the system by cheating. Yet if everyone did, the system would break down entirely. There are, as you may imagine, some very interesting dynamics and mathematics governing this system.

Finally, a roving madsnail goes on a rampage wantonly destroying the beautiful slime mold gardens. Stupid animals.

Incidentally, D. discoideum is the species I wrote about in January in which some strains were recently discovered to practice agriculture, or something close to it, by taking bacteria of their preferred noshing type with them in their spores so they have a guaranteed food source when they land. And still more recently, scientists published an article in Science (see here and here) they may even have tissues — and use two signaling or regulatory proteins related to the ones animals use to organize their embryos during development. This seems to mean the common ancestor of slime molds and animals (whatever *that* might have looked like) was using ancient versions of these proteins to arrange itself, and its descendants — both slime molds, and you — inherited these same proteins and are still using them to organize their bodies, in their different ways.

Cellular slime molds represent one of life’s many experiments in multicellularity. You are the product of another. So are plants. And so are fungi, and brown and red algae and some blue-green algae — and there are many more. Other experiments seem to have been abortive; recently this article revealed that blue-green bacteria (aka cyanobacteria) dabbled in multicellularity many times. Remember: evolution isn’t a goal-directed endeavor, although in certain etremely successful groups (vertebrates, beetles) it may seem that way.

To see a different cellular slime mold species that makes violet sporangia on slime mold candelabra, see here. Spectacular.

Finally, I’d like to note I have a new favorite German word : Schelim. As in “schleim mold”. : )

HT to this post at Small Things Considered for the discovery of this wonderful and educational German film.

Tagged as: Amoebae, Charismatic microfauna, social amoebae