Corals throughout the world are in decline for a number of reasons including microbial disease and environmental pressures. Different methods that have been proposed in recent years include those such as antibiotic treatment and immunisation. However, due to the quantities of antibiotics needed to treat a whole reef, the effects of antibiotics on non-pathogenic species and the lack of an adaptive immune system with regards to immunisation, these methods are not viable for effective coral disease management. This paper explores the idea of phage therapy as a treatment of pathogens associated with coral bleaching. Recent research by the authors indicated that coral pathogen specific phage effectively inhibits coral disease and, therefore, this paper further explores whether this theory can be scaled up and still remain relevant. The research investigates the relationship between the Red Sea coral Favia favus, the causative agent of white plague like disease (γ-proteobacterium Thalassomonas loyana) and the bacteriophage BA3.
To determine phage adsorption starved Thalassomonas loyana were taken and added at different concentrations to different concentrations of phage. Samples were taken at different time intervals and plaque assayed with the results used to determine a rate of adsorption of 1.0x10-6 phage per ml per min. This shows that when higher concentrations of T.loyana than phage are present there is less free phage in the water and shows that the starved bacteria do not down regulate viral receptors during nutrient stress.
The effects of inoculating healthy coral with T.loyana contaminated water and the subsequent protection provided after addition of phage at different stages of infection were then studied. The results showed the white plague like disease progressed rapidly leading to tissue lysis after 4-6 days in coral that had not been treated with phage and in coral where phage had been added 2 days post infection. However, these effects were prevented if the phage was added to the coral 24 hours after the initial inoculation and where phage was added as soon as the pathogen was introduced to the aquaria.
Finally, coral to coral transmission of disease was explored by adding healthy coral to an aquarium containing diseased coral. Once more, when phage was not added to the aquarium within one day the corals showed signs of the disease and died within two weeks. When the phage was added to the healthy coral within one day then transmission of the disease was inhibited.
This paper shows that phage treatment could only be effectively used to prevent and control the transmission of coral diseases locally as, if not noticed within 24hrs, any addition of phage would be ineffective as the coral’s fate has already been decided.
Previous studies by the authors also suggests that the fast mutation rate of T.loyana (3.7 x 10-6 per generation) conferring resistance to phage-receptor binding would , therefore, require the use of other T.loyana specific phage to be used in conjunction with BA3 treatment.
This paper shows that things aren’t as simple as they first appear and that more field work needs to be carried out to determine the overall effects of phage treatment on the management and conservation of the world’s endangered coral ecosystems.
A review of - Efrony, R; Atad, I; Rosenberg, E. Phage Therapy of Coral White Plague Disease: Properties of Phage BA3. 2009. curr. micro. 58:139-145.
2 comments:
Catchy title! I like how this post explored ways of possibly overcoming coral bleaching without the use of antibiotics, which although it way work in lab conditions there are problems when it comes to using it in the field, as you have mentioned.
I also found it interesting that the viruses were only effective if administered within 24 hours of infection so this treatment would be difficult to carry out in the field. It would be interesting if another study was carried that included a mixture of viruses speific to T.loyana and to see if this might increase the length of time after infection that the viruses were an effective treatment, whether having multiple phages might overcome the bacterias fast mutation rate.
Phage therapy is very definitely being actively explored in various areas and it there are signs of commercial uccess in the field of medicine and food spoilage. However, the need to continually keep ahead of bacterial evolution by having an ever changing 'cocktail' of phages is a real problem. That has worked in human medicine, I am sceptical as to whether it is possible for coral diseases. Similar problems have occurred in other areas of aquaculture (see REF Box 14.2 in my book). This US company claims it is v. successful in agriculture, so maybe it is possible. http://www.omnilytics.com/home3.html
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