Dictyostelium (also known as social amoeba)  is a primitive eukaryote, living as a single cell organism while bacteria, its source of nutrients, is present in the soil. When bacteria are consumed, starvation triggers a complex response allowing the cells to aggregate by chemotaxis and form a multicellular structure. Once the mound of cells is formed, this organism goes through a series of developmental stages based on coordinated morphogenesis and cell differentiation, to give rise to a fruiting body composed of a stalk supporting a ball of spores.  Dictyostelium is easy to manipulate allowing genetic and biochemical approaches necessary to achieve complete understanding of gene function. Moreover, Dictyostelium is helping scientists to understand the molecular bases of human disease.


Much more information about this organism can be found at the Dicty-base, a central resource for the genomics and biology of Dictyostelium.

 

Dictyostelium

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Dictyostelium fruiting body

“Genetic manipulation in Dictyostelium allows the study of  conserved genes, some of them relevant to human disease”

“Dictyostelium cells feed on bacteria by phagocytosis, a process also relevant to mammalian cells, such as neutrophils and macrophages. Defects in this process give rise to small plaques when Dictyostelium is grown on a bacterial lawn as shown in the picture where two mutant clones (the small ones) grow besides a  normal-sized wild type”                                                                                                                                          

“Dictyostelium cells divides by binary fission and the proper function of this process is important for correct growth and genetic stability. In Dictyostelium when this process is impaired, enormous cells might arise containing dozens of nuclei as the one shown on the left”                                                                                                                                       

Dictyostelium lives in the soil, an environment which is highly variable in its osmotic conditions. Diverse mechanisms have evolved to protect the cells from these changes, including a specific organelle, the contractile vacuole that expels water out of the cell. Mutants in this process can not survive hypotonic conditions and the cells explode as can be seen in the right panel of the figure (as compared to wild type on the left).                                                                                                                                        

“Dictyostelium cells have developed an extraordinary process of chemotaxis and motility to predate bacteria and to aggregate under starvation conditions. Defects in these mechanisms might generate strains unable to enter the multicellular development as can be seen in the mutant below”                                                                                                                                       

“During aggregation cells polarize and move in concert towards the aggregation centers. This process is compromised in the mutant shown on the left panel as compared to the wild type shown on the left. Cell motility and chemotaxis have been conserved  during evolution between Dictyostelium and cells from the immune system and this makes Dictyostelium an excellent model to study these essential biological aspects”