Ramos-Guzman, A.; Aguilera-Cortes, P.; Farias, S.; Perez, I.; Barros, V.; Riveros, B.; Soto, T.; Hernandez, M.; Berrios-Pasten, C.; Rojas, D.; Marcoleta, A. E.; Chavez, F. P.

Extracellular traps (ETs) were originally described in neutrophils as DNA-based structures that immobilize microbes and contribute to innate immunity. Subsequent studies revealed that ET formation occurs across diverse immune cell types and can proceed through non-lytic mechanisms involving mitochondrial DNA release. Whether ETosis also operates outside classical immune contexts and what its ancestral functions may be remain incompletely understood. Here, we show that vegetative, phagocytic cells of the social amoeba Dictyostelium discoideum, a professional bacterial predator with phagocytic mechanisms conserved with those of mammalian innate immune cells, deploy extracellular DNA traps in response to bacterial cues. ET formation is selectively induced by specific lipopolysaccharide variants, is not triggered by canonical neutrophil NET inducers, and occurs through a vital ETosis mechanism that preserves membrane integrity and feeding capacity. Ultrastructural analyses provide the first visualization of extracellular traps in Amoebozoa, revealing extracellular filamentous networks that physically capture bacteria. Molecular characterization demonstrates that amoeboid ETs are enriched in mitochondrial DNA and harbor a dynamic proteomic repertoire dominated by mitochondrial components, DNA-associated proteins, and multiple antibacterial effectors. Notably, ET composition varies with the bacterial stimulus, indicating that ETs are not static structures but rather responsive extracellular assemblies. Together, these findings establish ET formation as a regulated response in a unicellular phagocyte and suggest that extracellular traps may have originally functioned in microbial management during feeding, prior to their elaboration as immune effectors in multicellular organisms.