Physarum polycephalum – Slimy Yet Smart

Slime mould (Physarum polycephalum) may sound disgusting, but by utilising its method of locomotion, we can plan out networks from highways to computer algorithms.

Slime mould may not strike you as the kind of organism that sounds conventionally appealing. Its name alone may even cause you to want to actively avoid it. This should not be the case, as slime mould is one of the most unexpectedly interesting organisms out there. To start with, they are bright yellow and so they are relatively easy to identify (see figure 1). In addition, slime moulds aren’t technically moulds at all, nor are they plants, animals or a type of fungus. They’re classed as a type of organism known as protists. Protists are generally single-celled organisms with highly complex cellular machinery used to undertake certain processes. Physarum polycephalum is a particular species of slime mould which is classed as a ‘plasmodial’ slime mould. This means these organisms are very large single cells with multiple nuclei. This occurs when individual cells congregate together and fuse with one another to create a larger form [1].

The fact that P. polycephalum is single-celled may come with some pre-conceived ideas. They are not complex organisms; they do not undertake interesting behaviours and they are microscopic and thus difficult to observe. None of these points are factually correct, in fact they could not be further from the truth. In a lab setting a P. polycephalum specimen was observed to grow up to 30cm in diameter, so observations are relatively easy and have yielded fascinating results. In addition, there have been many lab studies conducted looking at the behaviour of P. polycephalum, many of which have focussed on the specimen’s movement in particular. The specimen consists of an outer layer of gel-like consistency and an inner layer of protoplasm. As the outer layer contracts and relaxes the inner layer undergoes streaming movements. This allows the organism to move freely [3] (see figure 2). The inner layer of protoplasm contains a complex network of tubes which transports both nutrients and chemical signals throughout the body. This internal communication means if the organism comes across a source of nutrients, it can relay this information to the rest of the body and it will form the shortest possible route from the main body mass to the nutrient source [4].

The network that P. polycephalum forms and the way in which it utilises this system has a multitude of applications across many fields of work. This is because networks form the basis of countless models from food webs in ecology through to the internet in technology. The principle of communication between multiple variables is so integral that it is no surprise that it can be translated to a number of different settings. One of these settings that is both surprising and ingenious is route mapping. In one study conducted by Adamatzky et al. [6] a sample of P. polycephalum was used to investigate the Mexican highway system. By placing nutrient sources on the main cities across the map and allowing the P. polycephalum specimen to spread out and form routes to each source, it was found that the network formed by the organism was incredibly similar to the pre-existing highways. A similar study was conducted with a model of the Tokyo railroad system, and again, the network produced by the slime mould was very similar to the layout of the established map (see figure 3) [7]. These studies along with their findings could be used in future route planning for different modes of transport in order to identify the most efficient routes from point A to point B. This could result in less fuel consumption, or a decrease in the time taken to travel. This kind of slime mould has even been used to inspire the improvement of a computing algorithm known as the ‘Shortest Path Problem’ [8].

The aforementioned examples of how slime mould is used in different ways to improve systems only scratches the surface. There are a huge number of possibilities as to how these organisms can be utilised. One thing is true though, it is truly astounding that a brainless, single-celled organism can display this behaviour and how it can have a rather profound impact on a number of scientific and technological fields. It may not be ‘intelligence’ per se, but there is no denying that it is an incredibly clever system.

References:

[1] Poinar, G.O. and Waggoner, B. M. 1992. A fossil myxomycete plasmodium from Eocene-Oligocene amber of the Dominican Republic. Journal of Protozoology 39(5): 639-642.

[2] “Yellow slime mold.” by Bernard Spragg is marked with CC0 1.0

[3] Yoshiyama, S., Ishigami, M., Nakamura, A. and Kohama, K., 2010. Calcium wave for cytoplasmic streaming of Physarum polycephalum. Cell biology international, 34(1), pp.35-40.

[4] Tero, A., Kobayashi, R. and Nakagaki, T., 2006. Physarum solver: A biologically inspired method of road-network navigation. Physica A: Statistical Mechanics and its Applications, 363(1), pp.115-119.

[5] “Slime mold plate culture” by Carolina Biological Supply Company is licensed under CC BY-NC-ND 2.0

[6] Adamatzky, A., Martinez, G.J., Chapa-Vergara, S.V., Asomoza-Palacio, R. and Stephens, C.R., 2011. Approximating Mexican highways with slime mould. Natural Computing, 10(3), pp.1195-1214.

[7] Tero, A., Takagi, S., Saigusa, T., Ito, K., Bebber, D., Fricker, M., Yumiki, K., Kobayashi, R. and Nakagaki, T., 2010. Rules for Biologically Inspired Adaptive Network Design. Science, 327(5964), pp.439-442.

[8] Zhang, X., Wang, Q., Adamatzky, A., Chan, F.T., Mahadevan, S. and Deng, Y., 2014. An improved physarum polycephalum algorithm for the shortest path problem. The Scientific World Journal, 2014.

[9] “map-overlays” by cesarharada.com is licensed under CC BY-NC-SA 2.0