Over the last few decades, the presence and prosperity of microbial diseases in the marine environment has increased. During the 1990’s a fungal pathogen, Aspergillus sydowii, infected sea fan corals throughout the Carribbean Sea. This spread was thought to be facilitated by environmental conditions, such as hurricane incidence and wind, inducing stress and increasing the susceptibility of hosts to immune-compromise. This study investigates the possibility that latent forms of Aspergillus sydowii may reside in the marine environment, on hosts or on symptomless carriers.
In 2000 it was first mentioned that filamentous fungi may be associated with marine sponges, and it is now known that fungi associations with sponges are not uncommon. Hundreds of fungi have been isolated from sponges in globally different locations; however the use of sponges as reservoirs for marine pathogens is yet to be shown, along with the ecological role of fungi present.
Several studies were carried out in the Bahamas using the sea sponge Spongia obscura. The first of which isolated fungi exhibiting the morphological and molecular phylogenetic characteristics of A. sydowii; which varies to terrestrial strains of the fungi. Metabolite secretions from the fungi were analysed and were found to be sydonic and sydowic acids, also characteristics of A. sydowii. Finally an inoculation experiment was carried out using 3 strains of the fungi (the one isolated, one from an infected sea fan and another which was non-pathogenic) to measure the radius of the infections caused. The combination of genetic data, chemical profiling and pathogenicity tests were used to support the conclusion concerning the presence of a coral pathogen, in a marine sponge.
The sponges where the fungi were isolated from were located 5Km away from coral reefs, therefore it is unlikely that the fungi found were present due to proximity or contact with the corals. A theory suggested for the sponges acquisition of these fungi, relates to the sponges high filtration rate and the presence of small particles of fungi originating from infected corals, dust, sediments, surface runoff or propagation within the sponge.
As sponges can be a hostile environment for fungi another experiment was carried out using semi-permeable dialysis tube to see if the strain could survive in the sponge. A second sponge species Iricinia stabilina was also used and the results showed that the sponge environments were no more harmful than in the controls used. The final experiment was designed to see if the fungal spores would be readily taken up by S. obscura’s filtration system, and whether it would survive contact without the tube barrier provided previously. Sponge samples isolated 20 minutes after exposure and 9 days later both showed similar results of a high number of colonies when compared with the control; indicating the fungi’s viability and sustainability within the sponge.
It has been shown that a live sponge can be a symptomless carrier of a coral pathogen, however it is still unknown what part the fungi plays in the sponge microbiota. It has been speculated that the sponge could act as a pathway allowing the fungi to hop between sponges as a mechanism of survival and dispersal in the aquatic environment.
Review of: Ein-Gil, N. Ilan, M, Carmeli, S. Smith, G.W. Pawlik, J. R, Yarden, O. (2009) Presence of Aspergillus sydowii, a pathogen of gorgonian sea fans in the marine sponge, Spongia obscura. International Society for Microbial Ecology, (3) pp. 752-755.
4 comments:
Great post Arainna. I Found this very interesting. The pathogens possibly using sponges as stepping stones between target corals is genius!
There must be some implication for the fungal pathogens being present on the sponges even if it is just taking up potential space for other microbes. It would be interesting to take a two sponges of the same species in the same location; one with fungal pathogens and one without and see the difference in community structure.
The house is already missing you Arainna!
Haha Hey Dave, missing the house too!
Yeah the concept is quite genius,utilising the surroundings species to allow itself a better chance of survival, plus dispersal. I think its a good suggestion but I do not believe it will be possible yet as I don't think that as a whole the community structure of the sponge is completely understood. It is so complex and as you will see in my next post community composition can vary due to external/environmental factors and species.
It's an interesting concept. Because sponges filter such vast amounts of water, this could presumably apply to other pathogens.Do the authors give any idea of how many fungi are in the sponge. surely, to be an effective smechanisms, the fungi would have to multiply and be released by the sponge. Is there any evidence that this happens?
The authors do not give much information on the numbers of fungi, they just said there was hundreds and that the isolate they referred to as Aspergillus sydowii was strain 382- However it is possible that strains of fungi were present more than once. The authors do mention the possibility of proliferation within the sponge and then release, but this was only mentioned. Although they did put across the idea that the fungi could be released when the sponge dies, which seems plausible however I was under the impression that sponges had quite a long lifetime. I looked for further research but unfortunately could not find any follow up studies on the topic.
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