The Arsenal of a Bacterial Predator Revealed by Cryo-Electron Microscopy

Davide Amendola

ETH Zürich

Ixotrophy is a bacterial predation strategy observed in a subset of multicellular, filamentous bacteria of the phylum Bacteroidota and is characterized by their ability to catch prey cells on their surface - like flies on flypaper - and subsequently lyse them to supplement their own nutritional needs. Accordingly, it has been proposed to be an elegant solution to the problem of low nutrient availability in aquatic environments, as well as an important mechanism regulating the dynamics of various microbial communities. The exact mechanisms that mediate ixotrophy, however, have remained largely elusive.

Here, we employed a state-of-the-art multi-scale imaging workflow to visualize and identify the macromolecular protein complexes involved in ixotrophy. We combined cryo-electron tomography and subtomogram averaging with single-particle cryo-electron microscopy to determine the structure of a novel grappling hook-like adhesin responsible for the catching of flagellated prey. By determining the primary amino acid sequence directly from the high-resolution density maps, we identified grappling hooks as the heptameric assembly of a single giant protein. Further, we used various bioinformatic analyses to show that its N-terminal domain resembles other bacterial adhesins, whereas its C-terminal domain directs secretion to the outer membrane via the Type IX Secretion System.

Go back