From Medicine to Architecture to Astronomy: the Blob That Does Everythng

Fiona Hamilton
5 days ago
6 min read

Physarum polycephalum is a single-celled organism that is often mistaken for a fungus. These myxomycetes are more commonly known as slime molds. Slime molds are amoebae that are remarkably similar to various fungi, which is why they were classified as such for many years. They release spores to reproduce, exist in damp areas, often on mulch in gardens, and grow off of dead plant material just like a fungus. However, while fungi produce enzymes that help break down dead plant matter into chemicals they can then absorb, slime molds literally consume them.

Slime molds are most famous among the public for the highly efficient roadmaps they ‘create’ for various countries. When crumbs of food are placed on a surface to represent major cities, a slime mold will send out tendrils connecting all of the food sources quicker and more efficiently than we do with our cities. Similarly, slime molds are great puzzle solvers and can solve any maze you throw at them, and do so better than you ever could.

The slime mold life cycle consists of four major stages. They start out life as little spores that activate once they reach a damp area, sometimes remaining dormant for up to seventy-five years. Slime mold spores are different from fungal spores in that they contain cellulose, an important part of the cell wall in plants. Once the spore reaches a satisfactory place to hatch, it becomes a myxoamoeba and is indistinguishable from a regular amoeba under a microscope.

This is where things start getting interesting. These little slugs are still single-celled organisms, and when split in two, can continue as two separate organisms. These baby slime molds are pretty much immortal and have mechanisms to survive some pretty extreme conditions. When things get tough, they can form a tail and swim it out, or for a hard cyst-like cell that will keep them moist in case things get too dry. The slime mold Myxamoeba is actually the slime mold’s form of sex cells, which, if you remember freshman biology, are called gametes. Unlike most species, which have two sizes of gametes, such as sperm and egg, all slime mold gametes are the same size. The word for this is isogamy, which means that they need other ways to know if two gametes can fertilize. This is no problem, though. Each gamete belongs to a certain mating type and generally has hundreds of compatible mating types. The only thing they need to do is find another gamete.

Once two slugy amoebas find each other, they fuse and finally become a full, diploid cell. The cell does not divide, but the nucleus does. One slime mold has thousands of nuclei in its single cell. Once the nuclei start dividing, the slime mold starts to grow. Adult slime molds can be anywhere from being like a big slug to the size of a large rug. Adult slime molds can be any variety of colors, though the yellow “dog vomit” slime is one of the more common kinds. However, slime molds cannot truly be green, since they don’t use chlorophyll.

Eventually, the amoeba moves on to the next, and final, stage of its life. Depending on the species, the slime mold will do one of two things. If it’s a plasmodial slime mold, the more classic large and blobby kind, it will become a sort of sphere-like or popsicle-shaped structure made of spores. The more interesting process belongs to cellular slime molds. They ooze along the forest floor at remarkable speeds of about one millimeter per hour. As they move along, they leave behind a chemical trail that can be picked up by other slime molds. When they come across a chemical trail they start to follow it, making their way towards another slime while amplifying the trail’s signal in the process. Once the slime molds all come together, they join together to form a faux plasmodium. They still remain individuals in the new giant slime, and about a third dedicate themselves to becoming the stalk of the structure. All of the remaining sacrifice themselves and become spores. The spores of either slime mold are then distributed through wind or passing wildlife, and the cycle begins anew.

The most studied of all these stages is probably the adult amoeba stage, of course. During this time, scientists can use it for a variety of things, including planning interstate roads. Sometimes they don’t even need a true slime mold to conduct their research and can just use a computer simulation of one, like in searching for dark matter.

Wait. What?! How could a slime mold help astronomers locate dark matter? Well, it turns out that the universe is structured in a way that is similar to how a slime mold connects food and suggests how we connect cities. The cosmic web is like the skeleton of the universe. Between galaxies and their clusters, there are fine threads of dark matter laced with gas that connect everything. We cannot actually see dark matter, but we can find gas. Even so, finding these small strands of material is extremely difficult when faced with just how big the universe is. Like finding a needle in a haystack, but worse. But now imagine the web as the slime mold’s little roads and the galaxies as cities. Using a computer algorithm to simulate a slime mold searching for food, but in a 3D space instead of the usual 2D one, astronomers found that they could find these cosmic strands much quicker than before. All thanks to a single-celled slime, of all things.

Back on Earth, however, slime molds could have an even greater importance in research, namely in better understanding cancer cells. Turns out, the fusion of slime molds into larger single-celled organisms follows the same mathematical model as that of tumors. Tumors need blood, and making sure they can’t get that blood can be an effective way to attack cancer, but sometimes difficult to do right. The important thing about slime molds, species Dictyostelium discoideum (A.K.A. Dicty) in particular, is the ability to go from a single-celled organism to a multicellular one. Scientists found that when a Dicty slime was starved, it went from being multiple single-celled organisms to a larger multicellular being in order to avoid starvation.

When starving, the slime has a burst of ROS (reactive oxygen species), which signals similarly starving slimes to come together and join. However, too much ROS can be harmful, and ROS bursts usually come with additional antioxidant production that helps control the ROS. By adding extra antioxidant glutathione, scientists were able to prevent the slime mold from coming together when starving. Then, by separating out materials in the antioxidant, they found that it was the cysteine in it that was preventing the slimes from joining, and furthermore, sulfur was a key element in the molds becoming a single mass. This information could be incredibly useful in combating cancer cells, as some specifically keep their sulfur metabolism.

From city planning to cancer, the slime mold is the least expected of informants, but it can do things that we are only just beginning to understand. As a species, humans seem to pride ourselves on our impressive brain-to-body ratio, yet, without a brain, the slime mold bests us in what seem like the most rudimentary of games. Despite their unattractive appearance and unflattering names, slime molds are more interesting than we often give them credit for.

Slime Mold Research Sources:

More Detailed Overview: The Blob: Slime Molds - Utah State University

Overview: Slime mold 101 - Biomimicry Institute

Overview: Slime Molds: No Brains, No Problem - PBS

Quick Facts: Introduction to “Slime Molds” - University of California Museum of Paleontology

Quick Facts: Slime Molds - University of Wisconsin-Madison

Life Cycle: Slime Mold Facts - University of Warwick

Roadmaps: Slime Mold Beats Humans at Perfecting Traffic Networks - Live Science

Astronomy: Slime Mold Simulations Used to Map Dark Matter Holding Universe Together - NASA

Cancer & Mathematical Equation: A Slimy Insight Into Treating Cancer - Science

Cancer & Sulfur: Starvation turns slime molds into multicellular organisms - Max-Planck-Gesellschaft

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