Endangered Natural Pharmacy Hidden In Coral Reefs

Coral reefs are teeming with life: they are home to over a third of all marine animal and plant species on Earth, despite covering less than one percent of the ocean floor. However, this immense diversity is under threat from rising ocean temperatures. Since the 1950s, half of the world's coral population has already disappeared.

Beyond the reef's visible inhabitants, countless microorganisms are also under threat. These often live in symbiosis with corals, sponges and other reef dwellers, which benefits them both. To defend against pathogens, predators and competitors, microbes produce a vast arsenal of natural products that could be of great benefit to humankind.

The magnitude of the potential loss of this "natural pharmacy" is demonstrated by a new study published in the journal external page Nature . Conducted by ETH research groups led by Shinichi Sunagawa and Jörn Piel, in cooperation with Lucas Paoli from EPFL and the Tara Pacific Consortium, this study identified new microbial species in corals which have the ability to produce novel substances.

Samples reveal a multitude of microbes

The researchers examined more than 800 coral samples collected ten years ago during an expedition by the research vessel Tara across the Pacific Ocean. Most of these samples came from reef-building fire or stony corals.

The team first sequenced fragments of microbial DNA from the samples. Using high-performance computers at ETH Zurich, they then reconstructed the genomes of 645 different species of bacteria and archaea. "For over 99 percent of these species, no genomic information was previously available. Essentially, they were unknown to science," says Sunagawa.

Every coral has its own microbiome

A comparison with open-ocean water samples showed that these microorganisms are not widely distributed across the Pacific; instead, they are found only within the reef. Furthermore, they tend to be restricted to a particular type of coral, with hardly any overlap between different coral genera. Sunagawa notes that these microorganisms typically inhabit the surface and gastric cavity of their coral hosts, forming a complex ecosystem - similar to the skin and gut microbiome in humans.

Genetic blueprints for natural products

However, the researchers were not content with simply describing new species; they also wanted to investigate the biochemical substances that these microbes might produce. By closely examining the genetic material for the "blueprints" behind these natural products, they discovered hidden treasure.

"We found more potential for the production of natural products in the genomes of coral reef microorganisms than we had previously found across the entire open ocean," says Sunagawa. One reason for this may be the high density of life in coral reefs: in such a crowded environment, an organism with a versatile chemical defence arsenal has a clear competitive advantage.

Only a fraction discovered so far

For Sunagawa, these findings are only the beginning: "In the latest study, we examined corals from just three genera. In total, however, there are several hundred known genera, comprising several thousand species." The microbiomes of other species-rich marine organisms, such as sponges, molluscs and algae, have also not yet been sufficiently researched.

The researchers are deeply concerned about the extent of these knowledge gaps, and their implications. If biodiversity in coral reefs continues to decline, it will mean the irretrievable loss of thousands of mostly unknown microbial species.

"Molecular research on coral reefs offers enormous potential for biotechnological and medical applications," says Piel. "We are under time pressure to tap into and protect this potential," urges Sunagawa. It is therefore absolutely vital for the protection of coral reefs to include the microbiome too.