Physarum polycephalum
Encyclopedia
Physarum polycephalum belongs to the supergroup Amoebozoa
, phylum Mycetozoa
, and class Myxogastria
. P. polycephalum, often referred to as the “many-headed slime,” is a slime mold that inhabits shady, cool, moist areas, such as decaying leaves and logs. It is sensitive to light; in particular, light can repel the slime mold and be a factor in triggering spore
growth.
for many studies involving amoeboid movement and cell motility
.
If environmental conditions cause the plasmodium to desiccate
during feeding or migration, Physarum will form a sclerotium
. The sclerotium is basically hardened multinucleated tissue that serves as a dormant stage, protecting Physarum for long periods of time. Once favorable conditions resume, the plasmodium reappears to continue its quest for food.
As the food supply runs out, the plasmodium stops feeding and begins its reproductive phase. Stalks of sporangia
form from the plasmodium; it is within these structures that meiosis
occurs and spores are formed. Sporangia are usually formed in the open so that the spores they release will be spread by wind currents.
Spores can remain dormant for years if need be. However, when environmental conditions are favorable for growth, the spores germinate
and release either flagellated or amoeboid swarm cells (motile stage); the swarm cells then fuse together to form a new plasmodium.
The force in amoeboid microplasmodia is generated by contraction and relaxation of a membranous layer probably consisting of actin (type of filament associated with contraction). The filament layer creates a pressure gradient
, over which the protoplasm flows within limits of the cell periphery.
The force behind streaming in the dumbbell-shaped microplasmodia is generated by volume changes in both the periphery of the cell and in the invagination system of the cell membrane.
using the shortest route possible when two pieces of food were placed at two separate exits of the maze.
biophysicists discovered that the slime mould appears to anticipate the pattern by reacting to the conditions when they did not repeat the conditions for the next interval. Upon repeating the conditions, it would react to expect the 60-minute intervals, as well as testing with 30- and 90-minute intervals.
spatially re-allocated over combinations of food sources that each had different protein
–carbohydrate
ratios. After 60 hours, the slime mould area over each food source was measured. For each specimen, the results were consistent with the hypothesis that the amoeba would balance total protein and carbohydrate intake to reach particular levels that were invariant to the actual ratios presented to the slime mould.
Similarly, in a preprint
that has not yet been scientifically peer reviewed, P. polycephalum are again shown to prefer food patches based on the nutrients present within the patches; in particular, the slime moulds are reported to prefer patches with herbs like valerian root that are known to have sedative properties.
and Steiner minimum trees.
In a 2010 paper, oatflakes were dispersed to represent Tokyo
and 36 surrounding towns. P. polycephalum created a network similar to the existing train system, and "with comparable efficiency, fault tolerance, and cost". Similar results have been shown based on road networks in the United Kingdom
and the Iberian peninsula
(i.e., Spain
and Portugal
).
". For example,
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
, phylum Mycetozoa
Mycetozoa
Mycetozoa is a grouping of slime molds.-Classification:It can be divided into dictyostelid, myxogastrid, and protostelid groups.The mycetozoan groups all fit into the unikont supergroup Amoebozoa, whereas most other slime molds fit into various bikont groups .-Utility in research:Dictyostelids are...
, and class Myxogastria
Myxogastria
Myxogastria is a class of Mycetozoa, itself a grouping of slime molds, that contains 5 orders, 14 families, 62 genera, and 888 species. Notable examples within Myxogastria include the genus Stemonitis and the species Physarum polycephalum...
. P. polycephalum, often referred to as the “many-headed slime,” is a slime mold that inhabits shady, cool, moist areas, such as decaying leaves and logs. It is sensitive to light; in particular, light can repel the slime mold and be a factor in triggering spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
growth.
Characteristics
This protist may be seen without a microscope; P. polycephalum is typically yellow in color, and eats fungal spores, bacteria, and other microbes. P. polycephalum is one of the easiest eukaryotic microbes to grow in culture, and has been used as a model organismModel organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
for many studies involving amoeboid movement and cell motility
Motility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...
.
Life cycle
The main vegetative phase of P. polycephalum is the plasmodium (the active, streaming form of slime molds). The plasmodium consists of networks of protoplasmic veins, and many nuclei. It is during this stage that the organism searches for food. The plasmodium surrounds its food and secretes enzymes to digest it.If environmental conditions cause the plasmodium to desiccate
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
during feeding or migration, Physarum will form a sclerotium
Sclerotium
A sclerotium is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until a favorable opportunity for growth. Other fungi that produce...
. The sclerotium is basically hardened multinucleated tissue that serves as a dormant stage, protecting Physarum for long periods of time. Once favorable conditions resume, the plasmodium reappears to continue its quest for food.
As the food supply runs out, the plasmodium stops feeding and begins its reproductive phase. Stalks of sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
form from the plasmodium; it is within these structures that meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
occurs and spores are formed. Sporangia are usually formed in the open so that the spores they release will be spread by wind currents.
Spores can remain dormant for years if need be. However, when environmental conditions are favorable for growth, the spores germinate
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
and release either flagellated or amoeboid swarm cells (motile stage); the swarm cells then fuse together to form a new plasmodium.
Streaming behavior
The movement of P. polycephalum is termed shuttle streaming. Shuttle streaming is characterized by the rhythmic back-and-forth flow of the protoplasm; the time interval is approximately two minutes. The forces of the streaming vary for each type of microplasmodium.The force in amoeboid microplasmodia is generated by contraction and relaxation of a membranous layer probably consisting of actin (type of filament associated with contraction). The filament layer creates a pressure gradient
Pressure gradient
In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location. The pressure gradient is a dimensional quantity expressed in units of pressure per unit length...
, over which the protoplasm flows within limits of the cell periphery.
The force behind streaming in the dumbbell-shaped microplasmodia is generated by volume changes in both the periphery of the cell and in the invagination system of the cell membrane.
Intelligence
Physarum polycephalum has been shown to exhibit intelligent characteristics similar to those seen in single-celled creatures and eusocial insects.Maze-solving
A team of Japanese and Hungarian researchers claims that a specimen of P. polycephalum was able to navigate a maze made of agarAgar
Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...
using the shortest route possible when two pieces of food were placed at two separate exits of the maze.
Event anticipation
By repeatedly making the test environment of a specimen of P. polycephalum cold and dry for 60-minute intervals, Hokkaido UniversityHokkaido University
Hokkaido University is one of the most prestigious universities in Japan. It can be seen in the several rankings such as shown below.-General Rankings:...
biophysicists discovered that the slime mould appears to anticipate the pattern by reacting to the conditions when they did not repeat the conditions for the next interval. Upon repeating the conditions, it would react to expect the 60-minute intervals, as well as testing with 30- and 90-minute intervals.
Nutrient regulation
P. polycephalum have also been shown to dynamically re-allocate to apparently maintain constant levels of different nutrients simultaneously. In particular, specimen placed at the center of a petri dishPetri dish
A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
spatially re-allocated over combinations of food sources that each had different protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
–carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
ratios. After 60 hours, the slime mould area over each food source was measured. For each specimen, the results were consistent with the hypothesis that the amoeba would balance total protein and carbohydrate intake to reach particular levels that were invariant to the actual ratios presented to the slime mould.
Similarly, in a preprint
Preprint
A preprint is a draft of a scientific paper that has not yet been published in a peer-reviewed scientific journal.-Role:Publication of manuscripts in a peer-reviewed journal often takes weeks, months or even years from the time of initial submission, because manuscripts must undergo extensive...
that has not yet been scientifically peer reviewed, P. polycephalum are again shown to prefer food patches based on the nutrients present within the patches; in particular, the slime moulds are reported to prefer patches with herbs like valerian root that are known to have sedative properties.
Simulation of road networks
With more than two sources, the amoeba also produces efficient networks. In particular, the pattern connecting multiple food sources was shown to form efficient network structures like cyclesCycle (graph theory)
In graph theory, the term cycle may refer to a closed path. If repeated vertices are allowed, it is more often called a closed walk. If the path is a simple path, with no repeated vertices or edges other than the starting and ending vertices, it may also be called a simple cycle, circuit, circle,...
and Steiner minimum trees.
In a 2010 paper, oatflakes were dispersed to represent Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
and 36 surrounding towns. P. polycephalum created a network similar to the existing train system, and "with comparable efficiency, fault tolerance, and cost". Similar results have been shown based on road networks in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and the Iberian peninsula
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
(i.e., Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
and Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
).
Integration with electronics
The organism's reaction to its environment has also been used in a USB sensor and to control a robot.Computing
In a book and several preprints that have not been scientifically peer reviewed, it has been claimed that because plasmodia appear to react in a consistent way to the each stimulus, they are the "ideal substrate for future and emerging bio-computing devicesUnconventional computing
Unconventional computing is computing by a wide range of new or unusual methods. It is also known as alternative computing. The different methods of unconventional computing include optical computing, quantum computing, chemical computing, natural computing, biologically-inspired computing, wetware...
". For example,
- It has been reported that plasmodia can be made to form logic gateLogic gateA logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
s. In particular, plasmodia placed at entrances to special geometrically shaped mazes would emerge at exits of the maze that were consistent with truth tableTruth tableA truth table is a mathematical table used in logic—specifically in connection with Boolean algebra, boolean functions, and propositional calculus—to compute the functional values of logical expressions on each of their functional arguments, that is, on each combination of values taken by their...
s for certain primitive logic connectives. However, in the preprintPreprintA preprint is a draft of a scientific paper that has not yet been published in a peer-reviewed scientific journal.-Role:Publication of manuscripts in a peer-reviewed journal often takes weeks, months or even years from the time of initial submission, because manuscripts must undergo extensive...
, when these primitive gates were connected to form higher logic functions, the plasmodium ceased to produce results consistent with the expected truth tables. Consequently, the composed gates were validated instead using a simulation speculated to model the streaming processes within a plasmodium. - An outline has been presented showing how it may be possible to precisely point, steer and cleave plasmodium using light and food sources.
General references
- Gawlitta,W, KV Wolf, HU Hoffmann, and W. Stockem. 1980. Studies on microplasmodia of Physarum polycephalum. I. Classification and locomotive behavior. Cell Tissue Res; 209(1): 71-86.
External links
- http://www.carolina.com/tips/01pdfs/August_2001_Tips.pdf
- http://www.educationalassistance.org/Physarum/PhysarumPlus.html
- Cellular memory hints at the origins of intelligence – The learning and memory potential of Physarum polycephalum
- slime mold – Slime shown negotiating a maze