New probiotic treatment could help regenerate coral after bleaching events

16 Aug 2021

Coral that has been bleached white. Image: Morgan Bennett Smith/KAUST

Global heating is contributing to coral bleaching, but new research from KAUST used a probiotic cocktail to treat the ‘post-heat stress disorder’.

The underwater coral reef ecosystems are home to a beautiful array of life. But global heating poses a substantial risk for coral and scientists are desperately trying to slow its worldwide decline.

Now, researchers from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have developed a probiotic cocktail that could bring coral back from death’s door.

The climate crisis is heating Earth’s oceans. When these temperatures increase, corals expel the algae living in their tissues, which causes the corals to turn white in a process of bleaching. While bleaching itself doesn’t mean corals have died, it does mean that they are under increased stress and more likely to perish.

In 2005, the Caribbean lost half of its coral reef in one year after a massive bleaching event, when the warm waters that are usually near the Virgin Islands expanded southward. Satellite data from the previous 20 years confirmed that the single event placed more thermal stress on the reef than those previous 20 years combined.

Treating coral bleaching

This is what the KAUST research intended to address. By manipulating the microbiome of coral, they hoped to increase its stress tolerance to survive such heat events.

The team selected six beneficial bacterial strains from the coral Mussismilia hispida and used them to inoculate experimental cultures in other samples of the coral. These coral were exposed to increasing heat over a period of 10 days, reaching 30 degrees Celsius before dropping back down to a more moderate 26 degrees Celsius.

Researchers then waited to compare corals that had received probiotics versus those that didn’t. Disappointingly, there were no initial changes.

“At that point of the experiment I thought, well OK, we’re seeing similar responses between the treatments,” said Erika Santoro, the study’s lead author, who is now a postdoc at KAUST.

“But then after we dropped the temperature, we observed a plot twist from the group that we treated with probiotic [cocktail]. That was a really nice surprise.”

A healthy piece of coral reef is shown, likely one that has recovered from a heat stress event using probiotic cocktails.

A healthy example of coral. Image: Morgan Bennett Smith/KAUST

A treatment but not a solution

The probiotic treatment helped the coral get back on its feet after a heat stress event, increasing the survival chances from 60pc all the way up to 100pc. The researchers interpreted these results as showing probiotics can mitigate the effects of “post-heat stress disorder” and restructure the coral’s metabolic processes.

The study detailed how the probiotic group of coral had a low expression of genes in cell death and an increased expression of genes that help with thermal stress. There was also incorporation of the beneficial bacteria into the microbiome of the coral.

Santoro emphasised that this measure would not be enough by itself to save coral across the planet, however.

“Using a probiotic is an effective tool to help corals deal with the heat stress, but we also have to consider other interventions,” she said. These include “protection and conservation, everyone being more aware and, most importantly, decreasing greenhouse gas emissions and trying to change our resource use”.

“Corals will need all of these interventions,” Santoro added.

Sam Cox was a journalist at Silicon Republic covering sci-tech news