Slime molds look kind of like vomit but they are pretty awesome. In fact, one of them is affectionately nicknamed “dog vomit slime mold.” While vacationing in British Columbia, my 2 year old son, exploring in the trees and shrubs, exclaimed “cupcake!” Knowing it was highly unlikely that there would be a cupcake there, and not wanting him to eat whatever he found, I rushed over to see a pine cone covered in a thick layer of whitish yellowish stuff. It did, in fact look a little like a piece of rather unappealing cake with thinly smeared white frosting and sprinkles of pine needles and soil from the forest floor.
Looking around, I found several other similar things growing, and some that looked quite different. One looked like coral, another had bubbles of clear, sticky liquid. As I observed them over several days, they changed, all eventually looking alike, and after more days, dried up completely to a pile of dusty powder that easily fell apart when disturbed. These were all the same slime mold, at differnt stages of its lifecycle. I’ve sent these photos to various slime mold experts, and it has been tentatively identified as Brefeldia maxima, the “tapioca slime mold.”
Slime molds are indeed slimy, in the picture at the left you can see the slime trail it leaves behind as it moves, but they are not mold. They are actually amoeba. These amoeba can exist in the single celled form but under the right conditions, the single cells will amass together. In some slime mold species, called plasmodial slime molds, the cells will actually fuse together to form a single, giant multinucleated cell. Others, called cellular slime molds, form a multicellular mass. Eventually, the slime mold will differntiate and form fruiting bodies, complex strructures in which spores will develop. Spores can then be released to disseminate the slime mold to new locations. What amazes me is the complexity of this process and the blurring of the lines between unicellular and multicellular organisms. You have a single celled organism, in which many individuals can come together into a multicellular (or single giant cell) form, now behaving as one organism that can differntiate to form complex structures like fruiting bodies and spores. Clearly, we can’t be thinking of microorganisms like these as “simple.”
Some recent studies further demonstrate the complexity of slime molds. The slime mold Physarum was used to map an optimal network between points, in this case the Tokyo metropolitan area. Food sources were laid out corresponding to the communities surrounding Tokyo, and Physarum was placed at Tokyo. The slime mold extended plasmodia, or branches, out to the food sources. At first the branches fan out randomly, making many connections, but eventually most plasmodia disappear, leaving only the most optimal connections between the food sources. The final map of the plasmodia turns out to be quite similar to the Tokyo area metro system. Physarum can also do this with the US interstate highway system, and the Canadian highway network (um, isnt there just one highway in Canada?) So an amoeba can simulate a networks developed by human engineers!
In my lab, a student is exploring using Physarum for a similar purpose. Vassar is looking ahead 50 years or so to plan development of the campus. Can we use the slime mold to provide suggestions to the landscape architects on where to place the pathways between buildings? Can the slime mold help me find the best way across campus? We will keep you posted on what we find!