Thursday, 14 November 2013

Are corals cooling the seas?

While searching for papers relating to symbiosis following Colins lecture yesterday I came across a really interesting paper linking symbiosis, the marine sulphur cycle and DMSP production that has strong evidence to suggest that it is not only algae that are responsible for DMSP production.

Dimethylsulphoniopropionate (DMSP) in an integral part of the sulphur cycle within the marine environment, which once metabolized to dimethylsulphide (DMS) is though to induce cloud formation and in turn may help reduce temperatures and also phytoplankton growth as part of a feedback mechanism (although this is still under contention).

Raina et al. have studied the Acropora corals of the indo-Pacific region as they acquire their symbiotic algae (Symbiodinium) from the environment following their larval stage.  Juveniles of two coral species, Acropora millepore and Acropora tenuis were cultured in an algae free environment and the absence of Symbiodinium was confirmed using five DNA markers.  DMSP levels were monitored and despite the total lack of symbionts, the larval corals still produces high levels of DMSP.  The levels detected were in fact greater than those reported for benthic algae found in the same region.  Once the larvae had settled the DMSP levels within the coral continued to increase (by 44% in A. millepore and 54% in A. tennis).

When subjected to thermal stress (32°C) over 6 days both species again showed a marked increase in DMSP levels.  They also exhibited a decrease in levels of the antioxidants acrylate and DMS; presumably this is attributed to their use in ROS detoxification.

To support the findings in the juveniles, adult corals were subjected to thermal stress until 84% of their Symbiodinium had been expelled and the remaining algal cells were all displaying signs of advanced necrosis.  Under these conditions the adult corals contained 68% more DMSP and 36% less acrylate than the control, confirming that the DMSP production in these corals is not just at one particular stage in its life.
Raina et al. then looked at the genetic level for evidence of homologous gene sequences that are found in other species.  These genes correspond to each of the enzymes in the four steps associated with the biosynthesis pathway for DMSP recently discovered within a diatom species.  They found orthologues for two of these genes, the first of which codes for an NADPH reductase enzyme that has many other orthologues in nature.  The second gene found however is thought to be specific to the DMSP pathway, and codes for methyltransferase which is responsible for regulating intracellular DMSP levels and until now has only been found in photosynthetic organisms and two eukaryotes.   The expression of this gene was initially high but decreased following settlement at a time when the coral would normally acquire its Symbiodinium. 

This research shows that the coral itself actually may contribute around half of the DMSP produced and I find it interesting that at a time of stress when the corals may have lost all symbionts they could still be capable of producing DMSP which has been linked to reducing water temperature as part of a feedback mechanism.  This could possibly give the corals time to recover and take on new symbionts that may be more tolerant to an overall increase in temperature. 



Raina, J. B., Tapiolas, D. M., ForĂȘt, S., Lutz, A., Abrego, D., Ceh, J., ... & Motti, C. A. (2013). DMSP biosynthesis by an animal and its role in coral thermal stress response. Nature.

6 comments:

  1. So do you think they are producing DMSP in place of the symbiont or as well as? Could you test to see if the DMSP related genes are still expressed as much when symbionts are present?

    ReplyDelete
    Replies
    1. From the paper it seems that they are producing DMSP before and after the acquisition of the symbionts. It would be interesting to look at gene expression under differing conditions certainly.

      Delete
  2. That's a really interesting post Lucy. I wonder why the corals would produce DMSP? What evolutionary advantage would they gain? Raina et al, 2010, suggest that DMSP/DMS plays a role in structuring the bacterial community associated with reef coral, which is important for the coral health and resilience. Maybe this could explain why the corals appear to maintain a certain level of DMSP?

    ReplyDelete
    Replies
    1. In the seminar today we reviewed the paper by Garren et al. which showed that a vibrio species exhibited chemotaxis and chemokinesis in response to DMSP allowing it to infect the coral which in turn would cause bleaching. This made me think about the way in which corals acquire their symbionts initially; could the production of DMSP by corals be used as a chemical gradient by the symbiotic algae as well as by the vibrio species? or could it also help the coral reacquire a more temperature tolerant symbiont following bleaching? could the genes have been transferred from one bacterial species to another by a virus maybe? I think i came out of the seminar with more questions than were answered!

      Delete
  3. It is an appealing idea that the DMSP production could cool the SST due to cloud formation and albedo effect over coral reefs, as predicted by the CLAW hypothesis. It's worth noting that new evidence has led some authors to dispute the importance of DMS in regulating global climate - check out this review by Quinn & BAtees, 2011 http://www.nature.com/nature/journal/v480/n7375/full/nature10580.html. However, there could still be a strong case to say that it might operate on a more local level (e.g. above a major reef system like the GBR). Are coral animals unique in evolving DMSP production because they been especially sensitive to major climatic change in the past? It will be fascinating to see if DMSP related genes are present in other Cnidaria or in other marine inverts.

    ReplyDelete
    Replies
    1. I agree it will be interesting to see where this research leads us. In addition I would like to see some research focusing on the vibrio species from the paper by Garran et al. that we reviewed today, and how it utilises the chemical gradient, I wonder if it is something controlled by a particular gene and if so does the fact that the vibrio species does not appear to metabolise DMSP indicate that such a gene could have been acquired fairly recently?

      Delete