Cell biology of cnidarian-dinoflagellate symbiosis by Simon K. Davy, Denis Allemand, Virginia M. Weis
Davy SK, Allemand D, Weis VM. Cell biology of cnidarian-dinoflagellate symbiosis. Microbiol Mol Biol Rev. 2012 Jun;76(2):229-61. doi: 10.1128/MMBR.05014-11. PMID: 22688813; PMCID: PMC3372257.
This was a comprehensive literature review conducted by well-distinguished researchers in the field, especially Virginia Weis. The main purpose was to bring a solid cohesive explanation of how the symbiotic relationship between cnidarians and dinoflagellates functions. This includes the initial adoption of symbionts all the way through the mutualistic interactions. Within this, the exchange of nutrients and compounds is discussed alongside the current gaps in knowledge that still ridden much of this section of biology. Most of the obfuscated information is on the precise workings of the symbiosis which will mostly be remedied through genetic analysis and sophisticated microscopy. The review ends on the note of coral calcification which relates more directly to the real-world practicality of research in this field. Since tropical coral reefs often lack nutrients this symbiosis helps the corals conserve and recycle nutrients in the environment and within themselves. There are risks that currently exhibit this environment outside of the lack of essential food. Among these risks include ocean acidification which will most significantly alter the calcification process and potentially the photosynthetic process for the symbionts. Another risk is nutrient pollution. This could allow for a surplus of algae blooms which could block light from penetrating into the water and be absorbed by the dinoflagellates within the respective cnidarians and therefore hinder the growth of these species is an already nutrient deficient environment. Algae blooms can also distort the O2 levels in the water because when a significant amount of algae dies the bacteria use O2 to help decompose the organism.
The authors do not have a significant methodology as this was mostly a literature review using their knowledge and outsides that have been conducted up this point on the cell biology of cnidarian-dinoflagellate symbiosis. The paper was broken up into four main sections where each one looked at a different facade of the symbiosis to provide a comprehensive summary of the process.
Since there was no experimentation and this paper was written by experienced experts in this field there is not much if anything at all to critique from the methodology. The gaps in current knowledge were mention, as there are quite a few. An example would be the establishment of symbiosis. After this study was published there have been advancements in some of these areas through genetic analysis done in the Guse lab. A big topic of discussion is how the symbionts communicate with the host which is mostly through the immune system specifically, porcine reproductive and respiratory syndrome. An example of the communication is partly through proteins called lectins but the signaling information on face value is a plethora of chemicals that all have different uses. Similarly, there is currently a lack of data or funding to identify the specific compounds translocated between the symbionts and host.
Due to the various aspects of the symbiosis that were discussed in this paper, I only focused my attention on the introduction to acquiring and broader context I wasn’t aware of before. This includes the detriment that nutrient pollution can have as it enhances the growth of benthic algae which occupies the same space as most sedimentary cnidarians. In addition to the quantification loss of coral cover which in the Pacific Ocean has declined by 2% every year (when this paper was published.) There is pertinence to understanding the cell biology of this symbiosis as it will help dictate how the health of corals will change and therefore the biota it supports. This field of study has been around since the 70s and 80s and the limiting factor right now is mostly understanding the processes on the molecular level. There is a firm idea of what is happening on a bigger general scale as there are 6 phases starting with the initial contact and then turns into phagocytosis. The paper then discusses the exchanges between the organisms. The symbionts translocate the photosynthetically made organic carbon to the host in return for nutrients like the Aiptasia’s ammonium waste and shelter. In order to photosynthesis, the aiptasia takes the inorganic carbon dioxide or bicarbonate in and transports it to the dinoflagellates, the exact details of the transport mechanisms are still not fully clear. Dinoflagettes can produce different compounds some of which are not known but intracellular dinoflagellates can produce glucose, alanine which is used by muscles and nerve systems, and organic acids.