June 10, 2019
A Symphony of Slime Molds
Posted by: Rock Delliquanti
Not long ago as I was tending to our vermicompost bins (a future blog post coming this summer), and I found a strange substance growing inside the bin. It looked like a yellow, spongy sludge that branched and forked like roots. It was coming from the inside the compost we were cultivating and, for lack of a better word, exploring outward. Over the next few days it puffed up, then shriveled, and then finally dissolved into a brown stain and was gone.
This spongy substance was Fuligo septica, also known as Flowers of Tan. Other names for it that have a more striking imagery are Dog Vomit Slime Mold and Scrambled Egg Slime. The presence of this slime mold is nothing to be concerned about in our compost or any compost as far as I can tell. This organism is a decomposer and is just helping the process along, albeit with an unusual appearance.
Slime molds are without a doubt one of the weirder things you can find in nature. They aren’t a plant, or fungus, or animal--they’re technically amoebas. And they’re single cellular, but they may not seem like it. The slime mold that I encountered, and that many other people have encountered in their yards, gutters, and gardens, was actually at a particular life stage called a plasmodium.
*^Fuligo septica growing out from our vermicompost bins in the garden. Photo by Rock Delliquanti
Plasmodia are formed in slime molds when the single celled slime mold fuse together. The nucleus (the control center of the cell) will then split many times without splitting that single cell. The end result is one massive cell that has many nuclei spread across it. We don’t know exactly what the triggers are for this formation, but slime molds like these can be found underwater, in deserts, and in snowbanks. However, in the United States people most commonly find them in damp, wooded areas with a lot of dead organic materials (for instance a compost pile).
We do know that when a slime mold enters this phase of its life, its purpose is to feed. The slime mold consumes bacteria, protists, various molds and fungi, small bits of organic matter, and whatever dissolved substances are around it which kickstarts its growth. These forms can get up to one square meter and as they grow outward, create more and more nucleic command centers--anywhere from 100 to several million!
What’s incredible is that the slime mold doesn’t just grow outward like a puddle; in fact, slime molds are able to sense nutrients and light and move themselves accordingly. Slime molds can locomote themselves away from bright areas that could dry them out and towards food sources
at incredible speeds of up to 0.1cm per second (for comparison, plants move at a top speed of 0.0078cm per second). The mold first explores its surroundings and then reassesses as it goes along--strengthening routes that lead to food and pulling back from less efficient or less profitable routes. This can sometimes look like anything from a thick carpet to an elaborate web of interconnected slimes.
It’s this purposeful reticulation that grabbed the attention of Atsushi Tero from Hokkaido University. He took advantage of the slime mold’s inherent ability to find efficient paths and to maximize resource allocation and wanted to see how it would fare with a human conundrum: Tokyo’s rail system. By creating a map that replicates the Greater Tokyo Area with oats representing major cities and light sources to represent prohibitive terrain such as mountains and lakes, he let the slime mold explore and create what it saw as the most efficient connections between the food sources while avoiding these impassable obstacles. The result was a slime mold map with a surprising amount of similarities to the actual layout of the Tokyo rail system.
*Figures showing a timelapse of how the slime mold spread, refined, and strengthened its connections between food sources.
*Tero, A, et al. 2010. Rules for biologically inspired adaptive network design. Science. 327:439-442.
So next time you are gardening, walking through the woods, or wherever you may be and you come across a strange, creeping, yellow slime, take a minute to appreciate the complexity and utter weirdness of the organism in front of you. Who knows, maybe it will become a city planner someday.