Postbiotics Show Promise For Supporting Heat Stressed Corals
Climate change remains a significant threat to the planet’s coral reefs, which are home to at least 25% of all marine species. While probiotics have proven effective in restoring corals in controlled aquarium settings, proving the effectiveness of this microbial therapy in natural ocean environments poses challenges. A study released in the journal Cell Reports on September 3 reveals that both live probiotic and inactivated postbiotic treatments enhance coral health, particularly when these organisms are experiencing thermal stress during a natural marine heat wave.
“We want a future with coral reefs in it,” says 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 are home to various beneficial bacteria, including those that assist them in adapting to their surroundings. The goal of microbial therapy is to rejuvenate not only the corals but also the microbiomes they support. In this context, probiotics refer to living microbial groups sourced from healthy corals, which can be used on corals that are under stress.
Conversely, postbiotics consist of inactivated probiotics and/or their bioactive elements. A key objective of the research was to determine if postbiotics could also enhance coral health.
“The possibility of using postbiotics is particularly exciting when we think about scaling microbial therapies,” Santoro says. “Inactivated microbial formulations could potentially offer practical advantages, such as longer shelf life, easier storage and transportation, and reduced production costs.”
Santoro and her team conducted a study on Acropora cf. valida coral in the central Red Sea during a heat wave in the summer of 2022. Over the course of the 15-day field experiment, the daily average seawater temperatures fluctuated between 87.6°F and 89.5°F (30.9°C to 31.9°C). The researchers extracted beneficial bacterial strains from Red Sea corals to create two types of probiotic treatments along with their postbiotic equivalents.
Following this, they assessed the health of the corals by examining their colouration—where white or “bleached” shades signify poor health—and measuring the photosynthetic efficiency of the algae residing within them. After 15 days of treatment, one of the probiotic formulas and one of the postbiotic formulations showed a significant enhancement in coral health.
“When an innovative idea like this actually works—particularly under field conditions—we are positively surprised,” Santoro says. “The most exciting takeaway is that this study opens a new avenue for coral microbial therapies.”
The researchers conducted genetic and metabolic analyses on the corals that received treatment, uncovering that both probiotic and postbiotic therapies altered their microbial and metabolic profiles in unique manners. Notably, the corals treated with postbiotics exhibited a rise in Cobetia strains, a bacterium that aids corals in withstanding heat stress.
According to Santoro, further investigation is essential to grasp the underlying mechanisms that contribute to the effectiveness of these treatments, particularly concerning 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 says.
[image: Acropora colony in the Red Sea – by J Clipperton]
