Why the Minotaur Needed Slime Mold

Photo Credit janthornhill.com

There’s just something about mazes. From PacMan to the hedge-labyrinths of yester-year, a good maze tantalizes the human mind. In fact, the combined esthetics and mental acrobatics of maze negotiation are so inspiring that for decades scientists have been harnessing the power of this puzzle. Yes, our trusty lab coat-clad comrades have tested the “intelligence” of many species using this age-old challenge, ultimately finding that we’re not the only ones capable of corn-maze escape. This prestigious group includes such proto-Einsteins as mice, guinea pigs, octopi, and… slime mold?

            What exactly is a slime mold? This is a harder question than you might think, as classifying these organisms is anything but straightforward. Broadly, they are eukaryotic organisms; like you and I they have a membrane-covered nucleus inside each cell that contains their DNA. Unlike you and I, they are not one organism made of many cells that are each part of a specific tissue (eg. bone, heart, or lung). Instead, they are either single cells or groups of cells that look more or less all the same. To complicate things further, they look vastly different at different points in their life cycle, even switching from life as individual cells to blob-esque communities. The labyrinth-saavy slime molds are in the latter state referred to as plasmodium.

            Although it sounds like something made up by a nineteenth century “psychic,” plasmodium is really an incredibly interesting, gutturally disturbing, and biologically useful body type. While the typical human cell has one set of chromosomes surrounded by one nucleus that is itself enclosed by one cell body, the plasmodium smashes this neat order into something straight out of science fiction. In this form, many cells exist as a community but share a single cell membrane. This means there is free exchange of nutrients and other materials through the goo inside the cell(s) without the inconvenience of actually having to ingest shared materials. This is somewhat akin to everyone in your neighbourhood getting together for a big group hug and then having all your skins fuse together. Although slightly terrifying, this situation has the advantage that only the ones closest to the BBQ have to eat for the whole group to be fed. But wait, there’s more! Due to the pseudo-multicellular nature of plasmodium, you can cut it up into tiny pieces, each of which will terrifyingly regenerate into new, whole healthy beings. Conversely, when two plasmodial slime molds meet they fuse together to form a single, larger plasmodium. The movie possibilities are truly endless.

            So what on earth does this have to do with mazes? The biological advantage of the plasmodium body is that a community can explore different directions while feeding back any nutrients to the rest of the group through tubes made of the cell body itself. The result of this behavior is a tubular complex that navigates the environment by building up the network in the directions of food, and breaking it down in “dead end” directions. Scientists have found that this actively re-optimizing network has properties similar to those used in modern computing, and yes, can be used to navigate mazes. One group is even comparing the patterns of slime mold plasmodium growth with those of roads on the Iberian Peninsula.

            While the research fields of Urban Planning and Microbiology are currently separated by several university blocks, who knows? Maybe some day we’ll be driving highly efficient highway routes first sketched out on Petri dishes rather than engineering pads.