A symbiotic and free-living lifestyle: release of the deep-sea tubeworm symbiont Candidatus Endoriftia persephone in Riftia pachyptila

For horizontally transmitted bacteria symbiotic life is facultative. For these symbionts, not only the establishment of symbiosis in each host generation anew, but also the escape from the host and re-inoculation of the environment are important processes. To avoid complete exploitation by the host, some of the host-associated symbionts must escape and re-inoculate the ambient environment, such as has been shown for the rhizobia-legumes or the Vibrio fischeri – bobtail squid symbioses. Here we study the connectivity between the free-living and host-associated population of the thiotrophic symbiont Candidatus Endoriftia persephone in the model system Riftia pachyptila from deep-sea hydrothermal vents of the East Pacific Rise. While uptake of a few free-living symbionts in aposymbiotic host larvae occurs during horizontal transmission, release or escape of symbionts back into the environment upon host death has never been shown. Therefore, we conducted several symbiont release experiments in high-pressure flow through vessels. Trophosome, the symbiont-housing tissue of freshly dissected animals was incubated on symbiont escape and recruitment plates (SERPs) in high pressure under cold ambient deep-sea conditions and warm vent conditions for 12 h to 10 days. The symbiont was detected in the water and on glass cover slips using fluorescent in situ hybridization (FISH) with a symbiont-specific probe. FISH with a host-specific probe was negative. About 15% of symbionts colonizing glass cover slips were in division. A comparison of symbiont morphotypes between the population on glass cover slips and the host-associated population in the trophosome revealed that mainly rods and to a minor degree small cocci divide in the trophosome, while the entire population of rods, small and large cocci proliferate after they escape the dead trophosome. These results suggest that symbionts are released rapidly within 12 h from dead host tissue. This escaped symbiont population is viable and capable of colonizing surfaces upon which it proliferates. We conclude that the free-living and host-associated symbiont populations are connected through transmission when the symbiont infects the host and through escape back into the environment upon host death.

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First Name: 
Julia
Last Name: 
Klose
Telephone: 
+43-(0)-4277-57106
Affiliation: 
Department of Marine Biology, University of Vienna, Austria
First Name: 
Mario
Last Name: 
Schimak
Affiliation: 
Max-Planck-Institute for Marine Microbiology, Bremen, Germany
First Name: 
Monika
Last Name: 
Bright
Affiliation: 
Department of Marine Biology, University of Vienna, Austria
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Ecological Interactions
Abstract ID: 
CBE5-132