In 1992, shortly after completing my PhD at the University of Vienna, Horst Felbeck (Scripps Institution of Oceanography) invited me to my first deep-sea hydrothermal vent cruise. Since then, I have joined 16 cruises, dove 13 times with HOV Alvin and worked with ROVs SuBastian, Jason and ROPOS. I have spent more than a year on R/V Atlantis and would like to thank the crew very much for their hospitality. I am extremely grateful to the following colleagues for inviting me: Craig Cary, Colleen Cavanaugh, Jim Childress, Horst Felbeck, Charles R. Fisher, Pete Girguis, Samantha Joye, Lauren Mullineaux, Scott Nooner, Kathlyn Scott, Stefan Sievert, Andreas Thurnherr. 

A Post Doc position in the lab of Charles R. Fisher at the Pennsylvania State University, USA in 1996, and fundings from the FWF Charlotte Bühler Program and a FWF project “Triphasic life cycle in vestimentiferans” between 1997-2003 lead to several papers on the trophosome, the organ that houses the thiotrophic symbiont Candidatus Endoriftia persephone and the nutritional interaction between symbiont and host using ¹⁴C bicarbonate pulse – chase experiments and tissue autoradiography. 

Bright, M.; Keckeis, H.; and Fisher, C.R. (2000). An autoradiographic examination of carbon fixation, transfer, and utilization in the Riftia pachyptila symbiosis. Marine Biology 136:621-632

The next FWF funded project “Triphasic life cycle in vestimentiferans” (1999-2003) led finally to the discovery of the transmission mode. Because tubeworm larvae like to settle in cracks and crevices of the basalt but are very small and difficult to sample we designed Tubeworm Artificial Settlement Cubes (TASCs). Our first deployment was in 2001. Tubeworm babies settled in the grooves of the cube that could be taken apart and collected. This design made it finally possible to elucidate the horizontal transmission mode in tubeworms.

Nussbaumer, A.D.; Fisher, C.R.; and Bright, M. (2006). Horizontal endosymbiont transmission in hydrothermal vent tubeworms. Nature 441:345-348

To better understand the relatives of Riftia we received funding for a further FWF project “Trophosome evolution in siboglinids” (2007-2012) to study the trophosome of Sclerolinum and Osedax.

Eichinger, I.; Klepal, W.; Schmid, M.; and Bright, M. (2011). Organization and microanatomy of the Sclerolinum contortum trophosome (Polychaeta, Siboglinidae). Biological Bulletin 220:140-153

The ITN Project “Symbiomics” (2011-2014) funded the PhD of Julia Klose. After elucidating how Endoriftia enters the larval host, we were curious to find out how the symbiont escapes the host upon host death. Therefore, we designed experiments with Symbiont Recruitment Plates SRPs in high pressure flow through vessels to simulate host dead under vent and deep-sea conditions. It tuned out that Endoriftia is capable of leaving the dead trophosome tissue. They can settle on cover slips and even proliferate, not only under warm vent conditions but also under cold deep-sea condition lacking sulfide.

As theoretically predicted and found in many symbioses with horizontally transmitted symbionts, also the Endoriftia population is polyclonal. With high coverage metagenomics and multilocus sequence typing we showed that each host houses a dominant strain and several low-frequency variants. The free-living populations are more variable that the host-associated populations.

Klose, J.; Polz, M. J.; Wagner, M.; Schimak, M. P.; Goller, S.; and Bright, M. (2015) Endosymbionts escape dead hydrothermal vent tubeworms to enrich the free-living population. PNAS 112(36):11300-11305

Polzin, J.; Arevalo, P.; Nussbaumer, A.; Polz, M. F.; and Bright, M. (2019). Polyclonal symbiont populations in hydrothermal vent tubeworms and the environment. Proceedings Royal Society London B 286:20181281

In our current FWF project “Endoriftia response to host-associated and free-living life style” (2018-2022) we aim to unravel how the symbionts manage to deal with various conditions in the host and how they leave the dead host and survive in free-living in deep-sea environments. Gene expression patterns in the symbiont from live hosts exposed to different chemical concentrations, from dead hosts, and from free-living hosts in the seawater as well as colonizing surfaces will inform about the physiology of the symbiont. Further we plan to investigate whether the symbiont can live heterotrophically, especially under environmental conditions that do not allow chemosynthesis. Therefore, a suite of experiments was carried out in high-pressure aquaria during two research cruises on the R/V Atlantis with the submersible Alvin and on the R/V Falkor with the ROV SuBastian to the Pacific Ocean. This proposed study will enhance our understanding on the evolution of this exceptional partnership.