Aspergillus flavus: Marine organisms or terrestrial migrants?

When thinking about marine organisms we very rarely think about fungi. They do occur and can have a detrimental effect on other marine organisms. Although fungi are present in marine environments a lot of the time these species have also been found in terrestrial environments. A prime example of this is Aspergillus sydowii, which has been attributed to causing aspergillosis in the sea fans Gorgonia ventalina although there is much debate on how the organism reaches the Caribbean as the fungus is also found in Africa. The most accepted theory is that spores are blown over from Africa in dust clouds. Evidence has however shown that fungi taken from terrestrial environments are unable to cause aspergillosis and that there are differences between the marine and terrestrial strains.

This study addresses this debate using another fungus which is thought to have a role in aspergillosis, Aspergillus flavus. The fungus is an opportunistic pathogen which may cause disease in humans if infected plant matter is consumed. The fungus is known to have a high tolerance of salt which would clearly make it well adapted to living in marine environments. The researchers have examined the relationship between isolates from marine environments to isolates from terrestrial environments using Amplified Fragment Length Polymorphisms (AFLP-PCR). They tested A.flavus found in many different terrestrial environments as well as that found in diseased and healthy sea fan tissue and seawater.

The results clearly showed the genetic differences between A.flavus found in all of the different environments. Despite expectations there was always some differentiation between individuals of the fungus within isolates implying that cloning of the fungus was not occurring in any of the environments. Although there were clear differences between the fungi found in different environments there does not appear to be any specific clade that is more common in sea fans (figure 2 in the article clearly illustrates this). It also shows that there are no distinct clades separating A.flavus found in diseased tissue than in healthy tissue implying that the fungus found in diseased does not have any more particular adaptations for pathogenesis. As well as this marine and terrestrial isolates do not seem to form different populations (as shown in figure 1). This suggests that there is not a particular clade of A.flavus that is better adapted to living in marine environments but that it is able to survive in a wide range of environments.

It is still not known whether Aspergillus sporulates in the water or whether the populations come solely from terrestrial environments. Due to the lack of differences between terrestrial and marine Aspergillus it is thought that the Aspergillus colonies in the sea are dispersed from the land but we know that Aspergillus spores are able to survive in deep sea conditions so it is a possibility that dispersal may occur from colonies in the sea as well, although more research is needed to confirm this.

Anabella Zuluaga-Montero, Luis Ramírez-Camejo, Jason Rauscher, Paul Bayman, Marine isolates of Aspergillus flavus: Denizens of the deep or lost at sea?, Fungal Ecology, Volume 3, Issue 4, November 2010, Pages 386-391