The free-living amoeba Dictyostelium discoideum is a very particular organism, where a single cell represents a single organism, but under certain conditions these cells group together and form multicellular structures that can even move as a single organism!
Amoebae
Now, in order to talk about D. discoideum we must first understand what an amoeba is. It is a very small and simple organism that belongs to the group of protozoa (unicellular organisms), more specifically to the Amoebozoa group. Unlike animals or plants that have many types of cells working together, an amoeba is only one cell that can do everything it needs to do to survive. These microorganisms move by projecting their cell membrane into structures that are called pseudopods, and they do the same for feeding, where they "engulf" the surrounding liquid with these psudopods. This feeding mechanism is called macropinocytocide.
Dictyostelium discoideum
In the case of D. discoideum, when the amoeba is in favorable conditions of nutrients and humidity, it will feed by macropinocytosis. The cells are maintained separately, dividing and from one cell 2 daughters arise, each as a single organism.
Now, when conditions are no longer favorable, a social cycle is triggered where cells will group together and multicellular structures will be generated that will end in the formation of a structure called fruiting body, which contains heavy spores that are like the seeds of a tree, when dispersed each one will give rise to an amoeba. This unusual cycle is called the social phase or developmental phase, where different intermediate structures are produced until the fruiting body is reached. Among these stages, the "slug" or "slug" stands out, which, as the word says, is a stage where the group of amoebae forms a small slug that moves to regions where environmental conditions are conducive to proliferation and there it will go on to form the fruiting body.
Within this social phase, amoebae develop an altruistic behavior, where some cells sacrifice themselves so that others may survive. Those cells that remain in the stalk of the fruiting body will not propagate, but will form the support of what will be pseudospores.
This behavior of D. discoideum makes it an organism that could be part of the links that marked the transition between unicellular and multicellular life. On the other hand, the great similarity of the molecular machinery of this amoeba with respect to that of the human, added to the fact that it is an organism easy to manipulate and non-pathogenic, makes it an excellent study model to study different diseases.
In case you didn't think it was complex enough, this amoeba can also reproduce sexually (yes, as you read!). Under certain humidity and light conditions, sexually compatible amoebae fuse to form a giant multinucleated zygote. This zygote is enveloped in a thick cell wall and becomes a structure known as a macrocyst. Within the macrocyst, meiosis and multiple mitotic divisions occur, generating genetically diverse haploid amoebae that are released when external conditions improve.
Author: Nicolás Crivaro, Professor of Biotechnology and Bioinformatics at UADE.
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