The Multiple Hosts of Candidatus Endoriftia persephone

Riftia pachyptila and Tevnia jerichonana are both species of tubeworms found in the unique environment surrounding deep sea thermal vents. As discussed in some resent blogs, R. pachyptila relies on a endosymbiotic chemoautotrophic bacterium for its carbon fixation and energy production and is found in a specialised organ called the trophosome. Following this discovery many studies have examined this remarkable relationship and in 2008 the symbiont was named Candidatus Endoriftia persephone (Robidart et al 2008). However, T. Jerichonana has received very little attention and very little is known about its symbiont.

This study had the purpose of comparing the endosymbionts and the geochemical environment of both R. pachyptila and T. Jerichonana to discover how their symbionts vary physiologically. T. jerichonana are found at sites of newly erupted thermal vents and they seem to favour the low oxygen levels and relatively high concentrations of sulphide. Sulphide being the electron donor compound needed for both species of tubeworms and their symbionts. As the thermal vent ages and becomes less active the surrounding environment shows increased levels of oxygen but sulphide levels decrease. This change in chemistry seems to be more favourable for R. pachyptila as they replace any previous populations of T. jerichonana found at the same site. The presumption of this would be that the bacterial symbionts of these two species would also differ to reflect the different chemistry of their environment.

Both tubeworm specimens were removed from thermal vents on the East Pacific Rise and their trophosome tissues was removed. The bacteria were separated from the trophosome cells by density gradient centrifugation which allowed comparisons to be made of the genomes and major proteins of the isolates. Further measurements of the environment where the tubeworms were collected were also taken to compare the chemistry of the two sites.

Habitat chemistry showed what had been previously described with higher levels of sulphide (~2mM) being present at the site of T. jerichonana sampling compared to a much lower sulphide concentration (0.01mM) at the site where R. pachyptila were removed. Temperature and pH also varied greatly between the two sites. Metagenomics of the two isolates showed that 16s rRNA subunits of the two were identical and key metabolic genes were 99.9% homologous. Protein analysis also showed almost identical abundance of metabolic enzymes. These results strongly suggest that the two species of tubeworm share the same species of symbiont despite the very different chemical environments they inhabit. The fact that the bacteria genes involved with sulphide oxidation differ by only 0.1% also suggests that the two species of tubeworm are able to create an identical trophosome micro-environment that suit the needs of the bacterium for sulphide metabolism. If that is the case then it may be possible that Candidatus Endoriftia persephone is a symbiont in many other invertebrate species.

In my opinion this shows that Candidatus Endoriftia persephone is highly important to the thermal vents ecosystem. The fact that it forms a symbiosis with two species that range the life span of the vents themselves shows a remarkable adaptation for life in these small environments. I think this is also highlighted by a previous blog which describes how this bacterium can also live freely in the water column before ‘infecting’ tubeworm larvae. It would be very interesting if T. jerichonana symbionts were somehow released into the water column and went on to infect a R. pachyptila larva. I imagine this would be next to impossible to study though.


A Review of:
Gardebrecht, A. Markert, S. Sievert, S. Felbeck, H. Thurmer, A. Albrecht, D. Wollherr, A. Kabisch, J. Le Bris, N. Lehmann, R. Daniel, R. Liesegang, H. Hecker, M and Schweder, T (2011) Physiological homogeneity among the endosymbionts of Riftia pachyptila and Tevnia jerichonana revealed by proteogenomics. The ISME Journal, 1-11.

Additional Reference:
Robidart, J. Bench, S. Feldman, R. Novoradovsky, A. Podell, S. Gaasterland, T et al (2008) Metabolic versatility of the Riftia pachyptila endosymbiont revealed through metagenomics . Environmental Microbiology, 3, 121-126.