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Seaweeds can attract friends and keep away enemies

14 May 2019

Two biologists from Plymouth Marine Laboratory (UK) and the GEOMAR Helmholtz Centre for Ocean Research Kiel (Germany) have shown for the first time that an aquatic plant (macrophyte) uses surface-based chemicals to specifically cultivate microbes on its surface that protect the plant against diseases. The study was published recently in the Journal of Ecology.
Agarophyton vermiculophyllum
Scientists show health-promoting microbial manipulation in aquatic plants for the first time

The composition of the microbial community living in or on a larger organism plays an important role for its health, such as the microbes that live in the intestines or on the skin of a person can have a considerable influence on his or her well-being. The knowledge about the connection between human microbiome and health is widespread even outside science. Just as for humans, the composition of the microbial community plays an important role for other animals and plants, too. However, the mechanisms driving the colonization remain unknown particularly in the case of aquatic plants.

Dr Mahasweta Saha from Plymouth Marine Laboratory  and Dr Florian Weinberger from GEOMAR Helmholtz Centre for Ocean Research have now shown that the red seaweed Agarophyton vermiculophyllum specifically cultivates microbes on its surface, with the aid of chemical substances, that protect it from other pathogenic microbes.

"This is the first empirical proof of this ability in an aquatic plant," said Dr Saha, the first author of the study.
In land-based plants, the deliberate manipulation of the microbiome by means of chemical substances to ward off disease had already been found. It was also known that seaweeds, such as the bladderwrack Fucus vesiculosus, can control the composition of the microbiome on their surface. However, the role of these recruited microbes for health maintenance was not known.

Natural disease defence mechanisms

For their study, Dr Saha and Dr Weinberger, supported by the Cluster of Excellence “The Future Ocean”, carried out a series of complex investigations on the seaweed Agarophyton vermiculophyllum at GEOMAR in Kiel, Germany. This seaweed is originally found in East Asia, but has recently invaded many coasts in the northern hemisphere, including Europe. The scientists used algal specimens from Korea and the German North Sea for their series of experiments.

Initially, they isolated and identified microbes from the surface of the seaweed from both the native and invasive range. They then identified those microbial strains that could cause diseases, such as tip bleaching. At the same time the scientists found that other microbial strains could subdue the effect of the pathogenic strains and thus, protect the seaweed.

In a final step, they investigated the relationship between chemical substances on the surface of the seaweed and the composition of the microbiome.

Dr Saha explained: "It was clear that some chemical compounds secreted by the seaweed promote the protective strains and deter the pathogenic."

"Even though this is the first proof of this ability with an aquatic plant, there are many indications that other species may have the same" said Dr Weinberger.

In many coastal ecosystems, seaweed is important as a water filter, carbon sink and breeding ground for other organisms. In addition, some species are becoming increasingly important in aquaculture.

Dr Saha concluded: "If we understand the natural disease defence mechanisms of seaweed better, natural stocks and seaweed farms may be protected more sustainably."


Related information

Saha, M., Weinberger, F. (2019): Microbial ‘gardening’ by a seaweed holobiont: surface metabolites attract protective and deter pathogenic epibacteria. Journal of Ecology, doi:10.5061/dryad.52j8p1r
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