Department of Biology, San Diego State University, San Diego, United States; Viral Information Institute, San Diego State University, San Diego, United States; Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule, Zürich, Switzerland
Fabian Eisenstein
Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule, Zürich, Switzerland
Department of Biology, San Diego State University, San Diego, United States; Viral Information Institute, San Diego State University, San Diego, United States
Giselle S Cavalcanti
Department of Biology, San Diego State University, San Diego, United States; Viral Information Institute, San Diego State University, San Diego, United States
Robert W Zeller
Department of Biology, San Diego State University, San Diego, United States
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States; Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, United States
Martin Pilhofer
Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule, Zürich, Switzerland
Department of Biology, San Diego State University, San Diego, United States; Viral Information Institute, San Diego State University, San Diego, United States
The swimming larvae of many marine animals identify a location on the sea floor to undergo metamorphosis based on the presence of specific bacteria. Although this microbe–animal interaction is critical for the life cycles of diverse marine animals, what types of biochemical cues from bacteria that induce metamorphosis has been a mystery. Metamorphosis of larvae of the tubeworm Hydroides elegans is induced by arrays of phage tail-like contractile injection systems, which are released by the bacterium Pseudoalteromonas luteoviolacea. Here we identify the novel effector protein Mif1. By cryo-electron tomography imaging and functional assays, we observe Mif1 as cargo inside the tube lumen of the contractile injection system and show that the mif1 gene is required for inducing metamorphosis. Purified Mif1 is sufficient for triggering metamorphosis when electroporated into tubeworm larvae. Our results indicate that the delivery of protein effectors by contractile injection systems may orchestrate microbe–animal interactions in diverse contexts.
