An international team has mapped the microbial landscape of coral reefs: an unexplored potential for future medicine.

Guardians of a life that goes far beyond the boundaries of the visible, the coral reefs They are not just a hotspot of macroscopic biodiversity. In fact, within the tissues of coral polyps, a microscopic universe equally complex and vital teems. A recent international study reveals that the secret to the resilience and chemical richness of these ecosystems lies in their microbiome: an unexplored reserve of molecules that could rewrite the future of medicine and biotechnology.

The coral reef microbiome: a submerged molecular library

To our eyes, coral reefs appear as marine landscapes of rare beauty, "devoured by fish and assaulted by the sea". In addition, coral ecosystems are vital biological infrastructures for the health of the ocean and for human economies, to which they provide underwater landscapes that attract thousands of tourists and large quantities of fish every year.

Despite covering less than 0,1% of the ocean surface, coral reefs are home to approximately 25% of all marine species Known: this means that a quarter of all ocean fish species depend on these structures at some stage in their life cycle. Many adult fish, such as some tuna, spend their early life there; others frequent reefs to feed (on small animals that populate the coral ecosystem or on the polyps themselves).

Additionally, coral reefs protect coasts from storms and erosion and "nourish" areas of the ocean that would otherwise be deserted. Today we discover that in addition to hosting the highest levels of marine biodiversity, coral reefs are also the matrix of a large variety of microbes, and produce chemicals that could prove very promising for medicine and biotechnology.

An international research team has discovered that different coral species host distinct microbial communities and previously unknown biomolecules. In short, the true biodiversity of corals may reside in their microbiome.

A rich microscopic ecosystem deployed to defend the sea's corals

As can be read in the study published on Nature, corals depend on diverse communities of microorganisms, which we collectively call microbiomeThese communities provide corals with vital nutrients (carbon, nitrogen, phosphorus, vitamins, amino acids) and act to protect the host organism, for example against some infectious diseases. A 2006 study concluded that microbes associated with reef corals produce bioactive metabolites to repel pathogens, predators and competitors.

Antitumor agents discovered in other reef invertebrates, such as sponges and soft corals, are currently in clinical trials, but we still know very little about the bioactive potential of coral microbiomes. Therefore, with the support of the consortium Tara Pacific, the research team analyzed microbiome samples collected between 2016 and 2018 from 99 different coral reefs across 32 Pacific Ocean islands, mapping the microbial landscape of reef-building corals on an unprecedented scale in an ocean that is home to 40% of the world's coral reefs.

Researchers have reconstructed the genomes of 645 microbial species, of which over 99% had never been characterized at the genomic level. As Dr. Maggie Reddy, of the Ryan Institute at the University of Galway,

When we compared our results with microbes found on other coral reef species, it became clear how little we still know. Of the more than 4.000 microbial species identified, only 10% have available genetic information, and less than 1% of the species found only in the Tara Pacific samples have been previously studied. This highlights a serious gap in our understanding and underscores the need for much more biodiversity surveys, especially in less studied regions.

Protecting the science of the future alongside the health of the oceans

The research highlights a critical, often overlooked, dimension of conservation: when coral reefs die, we don't just lose corals, sponges, algae and fish; we lose a vast “molecular library” linked to microbial life. Furthermore, the biochemical characterization of previously unknown enzymes and compounds suggests immense untapped potential for biotechnology and medicine.

"The biosynthetic potential of reef-building coral microbiomes is equal to or greater than that of traditional sources of natural products such as sponges. Among the biosynthetically rich bacteria present in the coral reef microbiome, we identified previously unknown microorganisms (e.g., Acidobacteriota) that co-exist with corals and produce novel enzymes with exciting potential biotechnological applications."

the professor explained Olivier Thomas.

Bacteria, archaea, fungi, viruses, and algae that live on the surface and within coral tissues are highly specialized partners of their hosts and are prolific producers of bioactive compounds. As Thomas pointed out,

“This research represents a clear call to action to protect our coral reefs, not only for their value as a unique ecosystem, but also to preserve the exceptional chemical diversity that could enable future scientific discoveries.”

Next month, Reddy and Thomas will join the Tara Coral Expedition in Papua New Guinea to collect and study more marine specimens.

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Researchers have reconstructed the genomes of 645 microbial species, more than 99% of which had never been characterized at the genomic level (Photo: Fernándo Herranz Martín / GNU General Public License)