Coral reefs build large underwater ecosystems.
In the last decades they have to struggle more and more with the consequences
of global warming as the spread of coral disease often related with a pathogen
of the Vibrio genus. One of these
pathogens is Vibrio coralliilyticus
which was isolated from different geographical regions and though its influence
on corals is an important point to investigate. With respect to the fact that
coral disease cannot be treated with antibiotics and that corals do not have an
adaptive immune system phage therapy might be a reasonable way to prevent coral
disease which was investigated by Cohen et
al. (2013).
In this study the V. coralliilyticus strain P1 was used, so was a purified bacteriophage
termed YC isolated from infected corals. Both were found on infected corals and
in the seawater around at the Great Barrier Reef, Australia.
This study was split up in three
main parts. The first one was the identification of the phage. The phage was
isolated from seawater of the Great Barrier Reef and observed with TEM to
determine its morphology. That shows that it belongs to the Myoviridae family.
Purification of the phage nucleic acid and gel electrophoresis were used to
show that the phage is a DNA phage with a small genome size of 11 kb. Furthermore
Cohan et al. observed that the
absorption rate amount 500 phage particles per bacteria cell per minute. The
phage was termed bacteriophage YC.
The second part was the investigation of the
effect of V. coralliilyticus strain P1
on the corals’ endosymbiont Symbiodinium.
The photosynthetic activity was measured by using an iPAM fluorometer. A
decrease of the photosynthetic activity was observed in the treatments with P1.
After 24 h Cohen et al. measured
a reduction of 90 % in the photosynthetic activity. There was no effect
detected when P1 was treated with Phage YC before adding to Symbiodinium.
To examine the efficiency on living
corals 6 month-old juvenile corals were observed. They were raised from larvae
and then brought out in the reef water of the Great Barrier Reef. At age of 6
months they were recollected and positioned in aquaria. They activity was
indirectly measured by investigating their photosynthetic activity using an
iPAM fluorometer as before. Changes in morphology were observed by using a
dissecting microscope and a digital camera. When the juvenile corals were
treated with P1 they immediately retracted their polyps and after 1 h they
began to expel their symbionts. After 9 h only the skeleton remained. The
addition of Phage YC to P1 before adding to the juvenile corals changed the
results. No changes were detected in the 12 h experimentation period.
After 12 h a slight increase of photosystem inactivation and also
expulsion of Symbiodinium and tissue
lesions were observed.
The study suggest that the addition
of Phage YC leads to a lysis of V.
coralliilyticus P1 what result in an inactivation of the Zn-metalloprotease
of the bacteria that normally leads to an inhibition of the photosystems in Symbiodinium. All in all Cohen et al. conclude that Phage YC is a good
treatment to prevent or stop spread of coral disease triggered by Vibrio coralliilyticus but that further
research is needed to examine whether this phage treatment is feasible and
possible in open coral reef systems.
This paper can be an approach on preventing
spread of coral disease. Having said this, it needs much more research on the
long-time effect of phage therapy. It is interesting that phage treatment has a
positive effect for a short-time period of 12 h as investigated in this
study but slightly negative effects were shown after 12 h in the juvenile
corals. This study does not seem complete because in their conclusion Cohen et al. do not mention these negative
effects. This gives the impression that the researches have not thought on
long-time effects and they wanted to publish as soon as possible without
finishing their work. As a conclusion I would say that this study is a base for
further studies on long-term effects of phage treatment where it can be shown
that phage treatment might not be as effective as suggested by Cohen et al.
Reviewed paper:
Cohen, Y.,
Joseph Pollock, F., Rosenberg, E., & Bourne, D. G. (2013). Phage therapy
treatment of the coral pathogen Vibrio coralliilyticus. Microbiologyopen,
2(1), 64-74.
Thank you for your review, I think the findings of this paper would be hard to apply to the natural environment. Although under lab conditions it does appear to show that the addition of the YC phage leads to lysis of V. coralliilyticus and therefore protect the coral. However as you mention the long term effects remain unclear and in need of further study.
ReplyDeleteI was wondering how specific these phages would be? And if they would be able to prevent other pathogens? I would assume you would need a kind of cocktail of them to deal with different pathogen.
I think as our understanding of disease in the marine environment continues to shift the old textbook examples of a single symbiont to single host organism including the idea a single pathogen is the cause of a disease, although may at times be the case it is now being suggested that many diseases are likely the result of multiple organisms working in multifaceted ways. The effect of the environment is also now shown to be an important factor in coral disease with increased temperature increasing coral susceptibility to disease. If the coral is stressed it may allow opportunistic to become pathogenic.
Vibrio coralliilyticus has been shown to be linked to disease however I think within the marine environment this is much more complex. Experimentation in the lab takes away factors which might influence results in the natural environment such as the effects of other organisms and environmental conditions.
I think it’s important to start shifting our view away from looking at the effect of one species and take a more holobiont approach a recent study (Lemire etal, 2015) of Vibriosis in oysters have found that diseases in oysters are often colonized by diverse population of Vibro strains as opposed to single isolates. The study by Cohen only focused on one pathogen however in the marine environment there are many interactions from microorganisms and I think further study would be needed to more fully understand the benefits the use of phages could have in such a complex environment although of course these study would be hard to achieve.
Reference
Lemire, A., Goudenège, D., Versigny, T., Petton, B., Calteau, A., Labreuche, Y. and Le Roux, F. (2014). Populations, not clones, are the unit of vibrio pathogenesis in naturally infected oysters. The ISME Journal, 9(7), pp.1523-1531.
Hi Alisha,
Deletethanks for your comment! I agree that it is difficult to use this phage therapy in the natural environment because of the lack of knowledge how other factors influence the efficiency. Additionally the phage does not seem to be really efficient on a long-time vue (as seen in the experiment that was conducted in this study). And of course, the specifity is another important factor, that has to be determined.
I also think, that this kind of therapy is not really appropriate to treat coral disease right now because there are so many uninvestigated factors and they do not mention that these diseases can be triggered by several pathogens. So this study can only serve as base for much more detailed research including more factors and also a time-period that is longer than 12 h.
Eleni
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