Probiotics shield corals from deadly tissue loss disease

Researchers have found the first probiotic treatment that stops or slows a disease that has been killing Caribbean corals, and prevents its spread to healthy corals. The new approach provides an alternative to currently used amoxicillin treatments without the risk of promoting antibiotic-resistant bacteria in the sea.

Stony coral tissue loss disease (SCTLD) has mystified scientists since it was discovered in Florida reefs in 2014. The pathogen causing it appears to spread rapidly through seawater. It has now killed hard corals – the reef-building corals with bony skeletons – in almost every stretch of the Caribbean.

“It’s creating what are essentially open wounds in the corals that eventually will spread and consume the coral until all you have left is a skeleton,” says Blake Ushijima at the University of North Carolina Wilmington. But Ushijima and his colleagues noticed that, even when infected, some fragments of great star coral (Montastraea cavernosa) never got sick. They collected samples of 222 bacterial strains on those disease-resistant fragments and found 83 had some antimicrobial activity, including a strain called McH1-7 that was particularly active.

When the researchers dosed live corals with McH1-7 and tented them inside a plastic bag, they found the probiotic treatment stopped or slowed the progression of SCTLD in 68 per cent of 22 infected coral fragments.

“More amazingly, it seems to protect healthy corals from infection,” says Ushijima. In their 12 lab trials, the probiotic prevented SCTLD from spreading to healthy corals, something antibiotics are not able to do. Because stony coral species are numerous and diverse, “it’s likely each species will need its own treatment”, says Ushijima.

Probiotics could also provide longer-term protection than amoxicillin paste, which is currently spread onto corals by hand, says Valerie Paul at the Smithsonian Marine Station in Fort Pierce, Florida. “The hope is that the probiotic can become incorporated into the coral’s microbiome and provide more lasting protection against disease.”

The treatment is now being tested on corals in the wild at reefs near Fort Lauderdale, Florida, and in the Florida Keys.

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