Unveiling the coral microbiome: Insights for combating coral bleaching in the Great Barrier Reef

Their work led them to discover two distinct clusters of co-existing bacteria, known as cell-associated microbial aggregates (CAMAs), within the tissues of Pocillopora acuta corals. 

While one group belonged to the well-known and widely observed Endozoicomonas genus, the other astonished the researchers—it belonged to the genus Chlamydiales, which includes the bacteria responsible for chlamydia infections in humans.

This revelation offers valuable insights into the complex coral microbiome and coral reef health, as it reveals the potential interactions and dynamics among various bacteria living within coral tissues.

Bacteria are of paramount importance to corals, as they play critical roles in safeguarding corals against pathogens, recycling nutrients, and producing vital compounds such as vitamins and amino acids. 

They commonly inhabit the corals' mucus and skeleton, but their presence within the tissues, particularly in the form of CAMAs, has intrigued scientists.

The newfound Chlamydiales bacteria, thriving in the tentacle tips of P. acuta corals alongside the Endozoicomonas bacteria, adds a new layer of understanding to the coral microbiome. Maire adds, 

"There is a possibility that this bacterium gets nutrients and energy from other coral-associated bacteria, and for those of us working to understand coral biology, the possibility that the bacteria living inside coral tissues are interacting with each other is quite thrilling."

The urgency to address Coral bleaching 

The urgency to address coral bleaching has never been greater. Rising sea temperatures significantly risk the Great Barrier Reef and other coral reefs worldwide. 

When corals endure prolonged exposure to high temperatures, they expel the colorful marine algae (zooxanthellae) in their tissues, leaving behind a bleached, white skeleton. Recovery from such bleaching events can take decades, if it occurs at all.

Armed with their newfound knowledge, the researchers hope their discovery will help combat coral bleaching by employing probiotics. Madeleine van Oppen, a co-author of the study, shares that Van Oppen, whose laboratory focuses on developing bacterial probiotics for corals, explains the potential application of their findings in addressing the coral bleaching crisis.

 "One of the focus areas in my lab is the development of bacterial probiotics for corals, helping to improve their resistance to thermal stress and survival rates caused by climate warming," She says. 

"We still know very little about the functions of coral-associated bacteria, and this new study will help us to figure out whether probiotics are a feasible solution and if bacteria such as Endozoicomonas are best placed to do the job."

This innovative approach could help mitigate coral bleaching and contribute to the long-term survival of these reef ecosystems.