Bacterial symbionts use a type VI secretion system to eliminate competitors in their natural host

Lauren Speare, Andrew G. Cecere, Kirsten R. Guckes, Stephanie Smith, Michael S. Wollenberg, Mark J. Mandel, Tim Miyashiro, Alecia N. Septer

Research output: Contribution to journalArticlepeer-review

110 Scopus citations


Intraspecific competition describes the negative interaction that occurs when different populations of the same species attempt to fill the same niche. Such competition is predicted to occur among host-associated bacteria but has been challenging to study in natural biological systems. Although many bioluminescent Vibrio fischeri strains exist in seawater, only a few strains are found in the light-organ crypts of an individual wild-caught Euprymna scolopes squid, suggesting a possible role for intraspecific competition during early colonization. Using a culture-based assay to investigate the interactions of different V. fischeri strains, we found “lethal” and “nonlethal” isolates that could kill or not kill the well-studied light-organ isolate ES114, respectively. The killing phenotype of these lethal strains required a type VI secretion system (T6SS) encoded in a 50-kb genomic island. Multiple lethal and nonlethal strains could be cultured from the light organs of individual wild-caught adult squid. Although lethal strains eliminate nonlethal strains in vitro, two lethal strains could coexist in interspersed microcolonies that formed in a T6SS-dependent manner. This coexistence was destabilized upon physical mixing, resulting in one lethal strain consistently eliminating the other. When juvenile squid were coinoculated with lethal and nonlethal strains, they occupied different crypts, yet they were observed to coexist within crypts when T6SS function was disrupted. These findings, using a combination of natural isolates and experimental approaches in vitro and in the animal host, reveal the importance of T6SS in spatially separating strains during the establishment of host colonization in a natural symbiosis.

Original languageEnglish (US)
Pages (from-to)E8528-E8537
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number36
StatePublished - Sep 4 2018

All Science Journal Classification (ASJC) codes

  • General


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