“We want a future with coral reefs in it,” said co-lead author Erika Santoro, a postdoctoral fellow at the King Abdullah University of Science and Technology in Saudi Arabia. “We urgently need to understand both the natural mechanisms that allow some corals to tolerate heat and how we can safely enhance those mechanisms.”
Corals host a number of 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, in this case, 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 was to see whether postbiotics could also boost coral health.
“The possibility of using postbiotics is particularly exciting when we think about scaling microbial therapies,” Santoro said. “Inactivated microbial formulations could potentially offer practical advantages, such as longer shelf life, easier storage and transportation, and reduced production costs.”
Santoro and colleagues treated Acropora cf. valida coral in the central Red Sea during a summer 2022 heatwave. 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 team isolated beneficial bacterial strains from Red Sea corals to concoct two probiotic treatments and their postbiotic counterparts.
Next, they 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.
“When an innovative idea like this actually works—particularly under field conditions—we are positively surprised,” Santoro said. “The most exciting takeaway is that this study opens a new avenue for coral microbial therapies.”
The researchers 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 kind of bacteria that helps corals tolerate heat stress.
More research is needed to understand the mechanisms behind the treatments’ success, Santoro said, especially for postbiotics.
“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,” Santoro said.
