A Type VI Secretion-Related Pathway in Bacteroidetes Mediates Interbacterial Antagonism

SUMMARY Bacteroidetes are a phylum of Gram-negative bacteria abundant in mammalian-associated polymicrobial communities,wheretheyimpactdigestion,immunity, and resistance to infection. Despite the extensive competition at high cell density that occurs in these settings, cell contact-dependent mechanisms of interbacterialantagonism,suchasthetypeVIsecretion system (T6SS), have not been defined in this group of organisms. Herein we report the bioinformatic and functional characterization of a T6SS-like pathway in diverse Bacteroidetes. Using prominent human gut commensal and soil-associated species, we demonstrate that these systems localize dynamically within the cell, export antibacterial proteins, and target competitor bacteria. The Bacteroidetes system is a distinctpathwaywithmarkeddifferencesingenecontentandhighevolutionarydivergencefromthecanonicalT6Spathway.Ourfindingsofferapotentialmolecular explanation for the abundance of Bacteroidetes in polymicrobial environments, the observed stability of Bacteroidetes in healthy humans, and the barrier presented by the microbiota against pathogens.