An endosymbiont in a dead host – what next?

Many organisms use endosymbionts to feed. So does the deep-sea hydrothermal vent tubeworm Riftia pachyptila. Inside of its body live the thiotrophic endosymbiont Candidatus Endoriftia persephone (Endoriftia). R. pachyptila provides all substrates required for chemosynthesis to Endoriftia and in return the endosymbiont nourishes R. pachyptila entirely with released fixed organic carbon (Klose et al., 2015). But what happens if the tubeworm dies? To investigate this Klose et al. conducted a study which deals with the releasing of Endoriftia after R. pachyptila’s death.

Klose et al. found that only live symbionts were released of the dead hosts. The releasing happened faster under experimental vent conditions (22 °C) - which imitate the natural conditions of R. pachyptila - than in experimental deep-sea conditions (4 °C). A high number of symbionts were released over a short period of time (half a day under vent conditions) which led to an increased number of free-living Endoriftia. The releasing of symbionts can be a mechanism to spread within the host population and to infect new hosts. The investigations were conducted in the laboratory simulating vent and deep-sea conditions. The scientists used FISH (fluorescence in situ hybridisation) and epiflourescence microscopy to detect the release of Endoriftia. In their conclusion they state that with the knowledge of this study they are now able to decrypt the ‘stability of this mutualism in situ’ (Klose et al., 2015).

This study gives an insight of adaption mechanisms of endosymbionts to new environments or within the host. I think it would be interesting to see whether other species of tubeworms and endosymbionts use the same mechanism to adapt and to spread the population. Furthermore I agree with Klose et al. that it is also important to see whether this mechanism of releasing occur in situ or not.

Reviewed paper:

Klose, J., Polz, M. F., Wagner, M., Schimak, M. P., Gollner, S., Bright, M. (2015). Endosymbionts escape dead hydrothermal vent tubeworms to enrich the free-living population. Proceedings of the National Academy of Sciences, 112(36), 11300-11305. http://www.pnas.org/content/112/36/11300.full#content-block