Mechanism of bacterial predation via ixotrophy

• Main Author: Lien, Yun-Wei
• Other Authors: Pilhofer, Martin, Hardt, Wolf-D., Tocheva, Elitza I.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ETH Zurich 2024
• Subjects: bacterial secretion system; mobile genetic elements; Cryo-electron microscopy; info:eu-repo/classification/ddc/570; Life sciences; North Atlantic
• Online Access: https://hdl.handle.net/20.500.11850/665955; https://doi.org/10.3929/ethz-b-000665955

The ocean is a heterogenous environment with nutrient concentrations that vary across time and space. Survival under nutrient-limited conditions is a critical issue for marine bacteria. Some of them are able to sense and swim towards nutrient sources, such as the feces of marine animals, while others have evolved the ability to predate on other microbes. Some known bacterial predators stick to the prey and then extract the nutrients from them; others invade the prey and consume the contents from the inside. Another predatory strategy would be to first catch the prey on the surface, followed by lysis of the prey, a behavior known as “ixotrophy”. Even though ixotrophic predators are widespread in aquatic environments all over the world, little is known about the molecular mechanisms involved in this intriguing behavior and how these predators shape their environment. To characterize the mechanisms of ixotrophy behavior in the marine bacteria Aureispira sp. CCB-QB1, we applied an integrative imaging approach across scales from micrometers to Angstroms in Chapter 3. First, we identified an outer membrane-anchored grappling hook-like extracellular structure, a substrate of type IX secretion system, which enables ixotrophic predators to catch their prey. Second, we described a type VI secretion system anchored to the cell envelope, conferring to the predator the ability to kill in a contact-dependent manner by contraction of the outer sheath and injection of the inner tube into the prey. Third, we discovered a new type of regulatory pathway, which shuts down the energy-consuming secretion system machineries used for ixotrophy under nutrient-rich conditions and turns them on again once they are needed for hunting the prey in nutrient-limited conditions via mobile genetic elements. Finally, we examined the consumption of the prey using Raman microspectroscopy and analyzed the environmental relevance of our in vitro results with a dataset collected from the North Atlantic Ocean. In Chapter 4, we attempted to identify the ...