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Lectins modulate the microbiota of social amoebae

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Science  27 Jul 2018:
Vol. 361, Issue 6400, pp. 402-406
DOI: 10.1126/science.aat2058

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Sticky bacteria tolerated as future food

Dictyostelium discoideum amoebae consume bacteria until the supply is exhausted. Then the amoeba cells clump together into a “slug” and initiate a complex multicellular reproductive phase. Specialized cells within aggregates rid the slug of any extracellular bacteria. However, some strains of amoeba tolerate live, intracellular bacteria. Dinh et al. discovered that these carrier strains bear surface lectins that bind Klebsiella bacteria, promote cell entry, and prevent the bacteria from being immediately digested. These bacteria then provide a future food source. Moreover, the internalized bacteria transfer DNA into the amoeba nucleus, resulting in transient genetic transformation.

Science, this issue p. 402

Abstract

The social amoeba Dictyostelium discoideum maintains a microbiome during multicellular development; bacteria are carried in migrating slugs and as endosymbionts within amoebae and spores. Bacterial carriage and endosymbiosis are induced by the secreted lectin discoidin I that binds bacteria, protects them from extracellular killing, and alters their retention within amoebae. This altered handling of bacteria also occurs with bacteria coated by plant lectins and leads to DNA transfer from bacteria to amoebae. Thus, lectins alter the cellular response of D. discoideum to bacteria to establish the amoebae’s microbiome. Mammalian cells can also maintain intracellular bacteria when presented with bacteria coated with lectins, so heterologous lectins may induce endosymbiosis in animals. Our results suggest that endogenous or environmental lectins may influence microbiome homeostasis across eukaryotic phylogeny.

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