Exploitation of Other Social Amoebae by Dictyostelium caveatum

Abstract

Dictyostelium amoebae faced with starvation trigger a developmental program during which many cells aggregate and form fruiting bodies that consist of a ball of spores held aloft by a thin stalk. This developmental strategy is open to several forms of exploitation, including the remarkable case of Dictyostelium caveatum, which, even when it constitutes 1/103 of the cells in an aggregate, can inhibit the development of the host and eventually devour it. We show that it accomplishes this feat by inhibiting a region of cells, called the tip, which organizes the development of the aggregate into a fruiting body. We use live-cell microscopy to define the D. caveatum developmental cycle and to show that D. caveatum amoebae have the capacity to ingest amoebae of other Dictyostelid species, but do not attack each other. The block in development induced by D. caveatum does not affect the expression of specific markers of prespore cell or prestalk cell differentiation, but does stop the coordinated cell movement leading to tip formation. The inhibition mechanism involves the constitutive secretion of a small molecule by D. caveatum and is reversible. Four Dictyostelid species were inhibited in their development, while D. caveatum is not inhibited by its own compound(s). D. caveatum has evolved a predation strategy to exploit other members of its genus, including mechanisms of developmental inhibition and specific phagocytosis.

Mechanisms and consequences of entosis

“…For example, the sporulating bacterium Bacillus subtilis can cannibalize neighboring bacteria in response to starvation, by secreting lytic factors that induce cell rupture and the release of nutrients into the environment (Gonzalez-Pastor 2011). Similarly, the cellular slime mold Dictyostelium caveatum cannibalizes neighboring amoeba by engulfing and degrading them in order to obtain nutrients when bacteria are scarce (Nizak et al 2007; Waddell and Duffy 1986). Dictyostelium amoebae also cannibalize neighboring cells when entering into an alternative starvation response called the sexual life cycle, where zygote giant cells engulf of up to hundreds of neighboring amoebae to form ‘macrocysts’, whose protective cell walls are constructed in part from recycled components of cannibalized cells (Erdos et al 1973; O'Day and Keszei 2012; Saga and Yanagisawa 1982).…”

Taking a bite: Amoebic trogocytosis in Entamoeba histolytica and beyond

“…Treatment with the actin filament polymerization inhibitor cytochalasin B inhibited both the nibbling process and the cytopathic effect (13, 14). A process termed “nibbling” has also been described in Dictyostelium caveatum during predation of other Dictyostelium species (Figure 3C) (15, 16). …”

Chew on this: amoebic trogocytosis and host cell killing by Entamoeba histolytica

“…Prior to this, there were reports of “nibbling, piecemeal” ingestion of red blood cells by N. fowleri and Hartmanella [51, 52]. A process termed “nibbling” has also been described in Dictyostelium caveatum during predation of other Dictyostelium species [53, 54]. Since amoebae do not form a taxonomic group, it is notable that nibbling processes have been observed in numerous amoebae from at least two eukaryotic supergroups, the Amoebozoa and Excavates.…”