Dictyostelium Discoideum - "Farming"

"Farming"

A 2011 report in Nature published findings that demonstrated a "primitive farming behaviour" in D. discoideum colonies. Described as a "symbiosis" between D. discoideum and bacterial prey, approximately one third of wild-collected D. discoideum colonies engaged in the "husbandry" of the bacteria when the bacteria were included within the slime mold fruiting bodies. The incorporation of the bacteria into the fruiting bodies allows the "seeding" of the food source at the location of the spore dispersal, which is particularly valuable if the new location is low in food resources. Colonies produced from the "farming" spores typically also show the same behavior when sporulating; colonies. This incorporation has a cost associated with it: those colonies that do not consume all of the prey bacteria produce smaller spores that cannot disperse as widely. Additionally, there is much less benefit for bacteria-containing spores that land in a food-rich region. This balance of the costs and benefits of the behavior may contribute to the fact that a minority of D. discoideum colonies engage in this practice. D.discoideum is known for eating gram positive as well as gram negative bacteria. But some of the phagocited bacteria, including some human pathogens, are able to live in the amoebae and exit without killing the cell. When they enter the cell, where they reside and when they leave the cell are not known. The research is not yet conclusive but it is possible to draw a general life cycle of Dictyostelium discoideum adapted for farmer clones in order to better understand this symbiotic process .

In the picture we can see the different stages. First in the starvation stage, bacteria are enclosed within D. discoideum, after entry into amoebae, in a phagosome the fusion with lysosomes is blocked and these unmatured phagosomes are surrounded by host cell organelles such as mitochondria, vesicles, and a multilayer membrane derived from the rough endoplasmic reticulum (RER) of amoebae. The role of the RER in the intracellular infection is not known, but the RER is not required as a source of proteins for the bacteria. The bacteria resides within these phagosomes during the aggregation and the multicellular development stages. The amoebae preserve their individuality and each amoeba has its own bacterium. During the culmination stage, when the spores are produced, the bacteria pass from the cell to the sorus with the help of a cytoskeletal structure that prevents host cell destruction. Some results suggest that bacteria exploit the exocytosis without killing the cell. Free-living amoebae seem to play a crucial role for persistence and dispersal of some pathogens in the environment. Transient association with amoebae has been reported for a number of different bacteria including Legionella pneumophila, many Mycobacterium spp, Francisella tubarensis, and Escherichia coli, among others. Agriculture seems to play a crucial role for pathogens survival as they can live and replicate inside Dyctiostelium discoideum making husbandry. Nature’s report has made an important advance in the knowledge of amoebas behavior, and the famous Spanish phrase “ you are more stupid than a amoebae” is losing the sense because amoebas are an excellent example of social behavior with an amazing coordination and sense of sacrifice for the benefit of the species.