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This video was recorded at Predavanja na Nacionalnem inštitutu za biologijo, Ljubljana. Symbiosis, the 'living together of differently named organisms' is ubiquitous. In the sea, thiotrophic symbioses involving sulfur-oxidizing chemolithoautotrophic bacteria and animal or protist hosts are manifold. They occur in a variety of ecosystems with oxic-anoxic interfaces. The endosymbiosis between the giant tubeworm Riftia pachyptila and its endosymbiont Cand. Endoriftia persephone is one of the most exciting and the most well studied thiotrophic symbiosis, despite the facts that they live at deep-sea hydrothermal vents and cannot be cultivated. In this presentation, I will give an overview on the challenges of working in a remote deep-sea ecosystem, accessible only through submersibles, working on a 'moving' platform like a research vessel to perform experiments and fixations for later studies in land-based labs at the University of Vienna. I will present some highlights of my research on transmission and maintenance of the giant tubeworm symbiosis. The animals are considered the fastest growing invertebrates we know of. However, they are mouth-, and gutless as adults. Instead of feeding by normal means, the symbionts fix carbon at high rates and translocate nutrients to the host. Both symbiont and host proliferate in a coordinated manner in the symbiont-housing organ, the trophosome and perform a cell cycle with terminal differentiation. Proliferation rates of the host are rapid matching those of cancer cells. While the host is obligatorily associated with its symbiont, the symbiont does not need its host for survival. Once little tubeworm larvae settle they are infected by a few symbionts from the environment through the skin, similar to pathogen infections. The symbiont migrates through several host tissues until it establishes itself in the visceral mesoderm surrounding the foregut and the trophosome is established and the gut is reduced. In small juveniles this process stopped by apoptosis of infected skin tissue. Once the host dies, the symbionts are released back into the environment. Both processes, the transmission to get into the host and the escape from the host, are crucial for understanding this fascinating symbiosis.

Disciplines:

• Science and Technology  / Biology