Aspergillus sydowii causing aspergillosis in corals-not such a fun-gi

Coral reefs have long been subject to threats from a wide range of sources, such as pollution and overfishing. However, they are also very much at threat from a variety of diseases. One of these diseases is that of Aspergillosis, caused by the fungus Aspergillus sydowii. The taxa of Gorgonian corals, found in the Carribean, are the corals that are most afflicted by this disease. The disease is well studied, but aspects such as origin, transmission and mechanisms of pathogenicity are still unknown. As a result, modes of controlling and preventing the disease are hampered (Rypien et al., 2008).

Rypien et al., (2008) looked into the generic structure of a global sample of A.sydowii and used them to look at any patterns of genetic diversity and relatedness between environmental isolates and disease causing isolates of the fungi. The samples came from diseased corals, infected humans and environmental sources and were characterized using microsatellite and polymorphic markers. Colony growth and microscopic structure were also recorded in order to distinguish between samples (Rypien et al., 2008). Therefore, the study used both molecular and morphological measurements to assess relatedness and diversity, giving far more detail and accuracy to the results compared to if only one of these measurements was taken. Single isolates were analysed as a single population, showing whether or not disease causing and environmental isolates differ. Results will allow knowledge of broader patterns of emergent diseases in a broader range of ecosystems. (Rypien et al., 2008)

They found a lack of evidence of any recent bottlenecks and isolation by distance, so infer that a single introduction of the disease was unlikely. They also found that diseased sea fans were interspersed with environmental isolates, therefore suggesting that the disease has had multiple introductions from terrestrial and marine environments. The differentiation between environmental and disease causing isolates was found to be very low. This presents a big problem, particularly in bioremediation and management of the disease. With the isolates being so similar genetically, it should therefore be assumed that any isolate of the fungi could cause disease. Rypien et al., (2008) describe A.sydowii as an opportunist, with a diversity of isolates that can cause disease. They conclude that the variation in disease prevalence is likely a result of environmental factors and host resistance.

This study raises points that show definite challenges to the management of this disease. With such similarity, distinguishing between disease causing isolates and environmental isolates is very hard, raising the issue that direct control and targeting of the disease causing fungi is equally difficult. As a result, in order to manage and reduce the effects and spread of the disease, the best form of control possible is to reduce the impact of environmental stressors. These include managing pollution, temperature etc, which are linked with increased variation in disease prevalence (Rypien et al., 2008) The study gives strong evidence further supporting the fragility of corals in a changing environment, and extends the evidence for the need to control the threats that are presented to them.

Rypien, K., Andras, J., and Harvell, C. (2008). Globally panmictic population structure in the opportunistic fungal pathogen Aspergillus sydowii. Molecular Ecology. 18, 4068-4078.