Scientists revive coral dying from heat using live bacteria

Scientists successfully applied probiotic and postbiotic treatments for the first time in open sea to save the marine life form.

Global warming is a major threat to the world's coral reefs, which support at least 25% of all marine life.

Although probiotics have previously been shown to rehabilitate corals in aquarium experiments, the research team explained that demonstrating such microbial therapy in the ocean was difficult.

But the study has established that both live probiotic and inactivated postbiotic treatments improve coral health — while they are under thermal stress during a natural marine heat wave.

Co-lead author Erika Santoro said: "We want a future with coral reefs in it.

"We urgently need to understand both the natural mechanisms that allow some corals to tolerate heat and how we can safely enhance those mechanisms."

She explained that corals host several beneficial bacteria, including types that help them adapt to their environment.

The aim of microbial therapy is to restore not just the corals themselves but also the microbiomes they sustain.

Probiotics are groups of living microbes obtained from healthy corals that may be applied to stressed corals.

Postbiotics, on the other hand, are inactivated probiotics and/or their bioactive components.

A major goal of the study, published in the journal Cell Reports, was to see whether postbiotics could also boost coral health.

Santoro, a postdoctoral fellow at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, said: "The possibility of using postbiotics is particularly exciting when we think about scaling microbial therapies.

"Inactivated microbial formulations could potentially offer practical advantages, such as longer shelf life, easier storage and transportation, and reduced production costs."

Santoro and her colleagues treated Valid Acropora coral in the central Red Sea during a heat wave in 2022.

Throughout the 15-day field experiment, daily average seawater temperatures ranged from 87.6°F to 89.5°F (30.9°C to 31.9°C).

The research team isolated beneficial bacterial strains from Red Sea corals to concoct two probiotic treatments and their postbiotic counterparts.

They then measured coral health by evaluating the animals' colors — white or "bleached" hues indicate poor health — and the photosynthetic efficiency of the algae that live inside them.

After 15 days of treatment, one of the probiotic and one of the postbiotic formulas had "significantly improved" coral health.

Santoro said: "When an innovative idea like this actually works - particularly under field conditions - we are positively surprised.

"The most exciting takeaway is that this study opens a new avenue for coral microbial therapies."

The research team also ran genetic and metabolic tests on the treated corals, which revealed that the probiotic and postbiotic therapies had restructured their microbial and metabolic profiles in different ways.

Specifically, postbiotic-treated corals showed an increase in strains of Cobetia, a type of bacteria that helps corals tolerate heat stress.

Santoro says more research is needed to understand the mechanisms behind the treatments' success, especially for postbiotics.

She added: "We see approaches such as probiotics and postbiotics as additional tools that could help improve coral resilience and support restoration efforts, while broader actions address the causes of climate change."