Intraspecies Antagonistic Interactions Driven by the Type VI Secretion System in Vibrio cholerae

• Author / Creator

  Hussain, Nora A.S.

• The type VI secretion system (T6SS) is a contact-dependent molecular weapon used by bacteria to transport a variety of effectors into neighbours. Attacked cells must have immunity proteins specific to each incoming effector in order to neutralize their cytotoxic effects. Vibrio cholerae, a ubiquitous species in temperate and tropical coastal waters, possesses a T6SS that includes at least three unique pairs of Effector-Immunity (EI) proteins. Maintaining a diverse population of EI in one location suggests that T6SS intraspecies competition can influence population structuring through spatial segregation. We investigated T6SS-mediated competition interactions in a pairwise manner for 14 isolates from a single population in Oyster Pond, MA, located off the eastern US coast. Of the 91 possible pairwise competitions, the majority of strains are unable to coexist, with some instances of isolates able to outcompete others, and minimal cases of coexistence based on predicted competitive outcomes of T6SS EI compatibility. This is due to rapid horizontal gene transfer (HGT) events allowing diversification of EI modules in a lineage-specific manner.

  Pairwise competition assays were performed on all 14 isolates, with the outcomes generally matching the prediction made based on their T6SS compatibility. One exception to this was a unique isolate with an extensive, but potentially not completely expressed, EI array. In all other cases, strains predicted to win outcompeted their opponents, isolates predicted to coexist experienced minimal reduction, and incompatible strains underwent a more diverse gradient of loss. A competitive fitness-based hierarchy of Oyster Pond resident strains demonstrates structured T6SS efficacy within the population. Temperature-dependent competitive outcomes suggest abiotic factors influence T6SS interactions, which will be useful to consider in future work. Together, this data presents the effects of T6SS-mediated competition on intraspecific structuring of environmental populations.

• Subjects / Keywords

  • Contact dependent competition
  • Microbiology
  • T6SS
  • Microbial ecology
  • Bacterial population structuring
  • Type VI secretion system
  • Environmental microbiology
  • Vibrio cholerae
  • Bacterial competition

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-zrxr-nx83

• License

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