Slime Mold Blog Post

by EG

From here

“Slime mold 2020!” “Elect Physarum polycephalum to make America great again!” Have you ever found yourself deeply concerned about the current leadership of the country? Have you ever been ashamed over the lack of intelligence possessed by the man sitting in the highest office of our nation? Worry no more! In this blog post, I will present a viable alternative to the current bozo who spends all of his time everywhere but Washington: the slime mold, Physarum polycephalum. P. polycephalum is a protist that has demonstrated the mastery of efficiency, the capacity to learn, and the ability to solve complex problems, all of which are qualities lacking in the current administration. If change is what you’re looking for, fear no more, Physarum polycephalum is on the scene.

You may find yourself asking, “What are protists?”. They are an immensely diverse group of organisms with only one defining characteristic: they are all classified as eukaryotic. There are many well-known organisms, like amoeba and algae, that fall under the category of protist. To be considered a member of the kingdom Eukarya, an organism must have highly organized cells with a nucleus containing genetic information and complex organelles to carry out cell processes. However, unlike human beings, protists are composed only of a single cell. With that, cell similarities virtually stop.

A simple description is that protists are anything that cannot be classified as animal, plant, or fungus. As you can imagine, that definition encompasses a wide range of diversity. For nutrition, protists can either use light energy via photosynthesis, similar to the process used by plants, or they can use energy in the form of nutrients “eaten” by the cell. In most cases, protists also have organelles called mitochondria that, if anyone remembers high school biology, are the powerhouses of cells, and act as a currency exchange. This exchange turns nutrients into the cell recognized currency of ATP. Even so, some protists lack mitochondria, but this typically only occurs in anoxic conditions. In which case, the organism uses a hydrogenosome that functions in a similar way to mitochondria. In addition, the diversity seen in this taxa carries over to reproduction. Asexual reproduction via budding, is most common, but sexual reproductive cycles have been observed, they just remain poorly studied.

As a member of the very diverse group described above, Physarum polycephalum has a diverse range of characteristics. As previously noted, it is a slime mold, so named because it leaves behind a thick mat of extracellular slime when it moves. It is a pretty yellow color that eats fungal spores, bacteria, and various other microorganisms. Already it sounds better than the orange cheeto currently entrenched in the White House, right? It spends most of its life in a plasmodium form. While in this form, the microbe eats, divides by mitosis, and remains largely sedentary. When nutrients become rare, the plasmodium goes into starvation mode, during which motility increases rapidly and mitotic division decreases. If the plasmodium is unable to locate nutrients, a majority of the organism will desiccate and spore formation will initiate. These spores are formed in structures called sporangia, which are designed to burst when agitated, thus spreading the spores to new, hopefully nutrient-abundant, environments. The spores can then survive for an indefinite amount of time until nutrients become available. This method of reproduction ensures the survival of the species (Guttes). While the mold is good at surviving, it has also been shown to be extremely smart through rigorous testing.

One good quality to have if you’re attempting to run a country is intelligence. Otherwise, things might get out of hand and you could end up needing to be babysat by your co-workers. A key requirement for intelligence is the ability to learn and change behavior based on prior outcomes, and surprisingly, Physarum polycephalum has shown this quality. The ability to learn has been traditionally regarded as a trait found only in organisms with higher order thinking and even then, not in every case. One specific type of learning is habituation: the diminishing physical or emotional response to a repeated stimulus. Human brains are great at demonstrating habituation. For example, the initial shock of learning that a presidential candidate has no decorum or tact caused waves of anger, but by now, we’ve just come to expect it and there is a progressively smaller reaction as each new idiotic moment comes to pass. P. polycephalum is no different. In a groundbreaking study by Boisseau et al., the data suggested that the mold displayed habituation to an unpleasant, but not harmful, stimulus.

To obtain these results, the authors cultured the mold on an agar plate and connected the original plate to a second plate containing a preferred food source by building an agar “bridge.” On average, it took the mold two hours to move from the first plate to the second plate using the bridge. Once the average time it took to move had been established, the agar bridge was filled with quinine and/or caffeine, both of which are compounds that irritate the mold, but do no harm to it. The same mold that initially took two hours to cross the pure agar bridge took over twice as long to cross the quinine/caffeine bridge, and even so, crossed the bridge in a thin line in an attempt to avoid the irritant. However, when the experiment was repeated multiple times with the same mold cultures, bridge-crossing times significantly decreased, and eventually matched the initial pure agar bridge-crossing times. These results suggest that the slime mold learned that even though the quinine and caffeine were unpleasant, the compounds weren’t going to hurt it and could be crossed to reach a food source.

Another requisite trait to have as the leader of a country is the ability to think on your feet and solve problems. These slime molds also have the capacity to problem solve using their past experiences as a reference point, if being able to learn and share knowledge wasn’t cool enough. Problem solving is another skillset that has previously been relegated to higher functioning organisms only. Again, human beings are generally pretty good at problem solving. We can easily adjust our environments to be more favorable for our survival; if we’re cold, we put on a sweater, or if we’re angry, we spew vitriol onto the internet via Twitt-- wait, never mind, that doesn’t solve anything. However, this mold is out to prove that instead of throwing a temper tantrum when things don’t go as planned, it can calmly solve the problem to get the desired outcome.

In an experiment done by Reid et al., it was shown that this organism relies on spatial memory to solve a U-shaped trap, a problem often used to test autonomous navigational ability in robotics. The way the test was set up removed the ability of the slime mold to rely on chemoattractant gradients to guide its movement towards food, which is what it typically uses to navigate. If you remember to a few paragraphs back, you’ll recall that the mold leaves behind a thick layer of extracellular slime as it moves. The authors noticed that when the organism is foraging for nutrients, it strongly avoids that extracellular slime. However, when all of the new territory has been explored, the plasmodium loses its aversion to the slime and will cease its avoidant behavior. The authors concluded that the mold was “choosing” to not go where the slime was present because it signaled that area had already been explored.

From here

Using that information, the authors modified the U shaped trap for their own purposes. The U-shaped trap put a desirable food source behind a U-shaped barrier. If the mold tried to rely on classic chemoattractant signals, it would repeatedly run into the barrier and remain hungry. If it could problem solve and work around the barrier, it would signal that the mold successfully used its spatial memory to escape the trap. Turns out, the mold did just that. Ninety six percent of the plasmodia reached the food within the experimental time limit of 120 hours. I wonder what would happen if we placed a certain president in a U-shaped trap. Would he use his brain to get out, or just sit down and say the trap is rigged against him? I’m inclined to choose the latter-- there’s naught in the way of a brain. Not a slime mold, though! Those guys actually get things done.

If it was even still a question of who (or what) would make a better president, consider the fact that slime molds are just plain efficient. Evolution demands that every resource is put to use, so it’s just second nature for the mold. Efficiency gets it done. As a president, you need to be able to get things done in a timely manner in a way that’s beneficial to the most people. A lack of efficiency can lead to the waste of precious resources and create a plethora of miscommunication. Ring a bell for anyone? Physarum polycephalum understands this and actively seeks to maximize its efficiency because it increases the likelihood that it will survive to propagate, thus keeping it fit and able to lead the country.

Think back to the study done by Boisseau et al. where P. polycephalum became habituated to quinine and caffeine. The researchers took their experiments a step further and tested how long the organism remained habituated to the chemicals. In a shocking development, they found that the mold had a long term memory and could pass their habituation on to other “virgin” molds that had never encountered caffeine or quinine. Even when the habituated mold was mixed with virginal mold in a 1:9 ratio, the entire new fusion mold became habituated to the chemicals. Further research is required to determine by what mechanism the transfer of knowledge occurs, but in the case of leadership, do we really care about how knowledge gets passed on or just that it does? Unless you’re a certain person obsessed with emails. Then it matters; it matters very much.

Even more proof of the mold’s capacity for efficiency was demonstrated by researchers in Tokyo. Through their research, they showed that Physarum polycephalum is more efficient than some of the world’s leading engineers. The mold will always form the shortest pathway between two food sources to optimize resources. To test this mechanism, researchers set up food on agar to mimic the major city centers of the greater Tokyo area and allowed the mold to grow. The connective filaments of the mold matched the public transportation, including roads and subways, present in and around Tokyo at a high rate, and was found to be even more efficient than the current city design (Wantanabe).

From here

At this point, there should be no doubt about who or what would make the best supposed leader of the free world. Slime molds, members of the domain Eukarya and kingdom Protist, have got it all. They’ve proven to have the capacity to learn, demonstrated a high intelligence, and are masters of efficiency. They doesn’t throw temper tantrums, unleash juvenile tweetstorms, or waste billions of taxpayer dollars. Slime molds are pretty to look at, just want to live their lives, and for you to do the same. Slime molds aren’t an ugly orange color, they don’t have any hands over which to obsess about their size, and would never engage in “locker room talk.” I don’t know about you, but I personally welcome a new era with the supreme slime mold overlord, Physarum polycephalum.

References

Guttes, E., Guttes, S., and Rusch, H.P. (1961). Morphological observations on growth and differentiation of Physarum polycephalum grown in pure culture. Developmental Biology 3, 588–614.

Boisseau, R.P., Vogel, D., and Dussutour, A. (2016). Habituation in non-neural organisms: evidence from slime moulds. Proc. R. Soc. B 283, 20160446.

Reid, C.R., Latty, T., Dussutour, A., and Beekman, M. (2012). Slime mold uses an externalized spatial “memory” to navigate in complex environments. PNAS 109, 17490–17494.

Watanabe, S., Tero, A., Takamatsu, A., and Nakagaki, T. (2011). Traffic optimization in railroad networks using an algorithm mimicking an amoeba-like organism, Physarum plasmodium. Biosystems 105, 225–232.