The strain known as MCH1-7 was first discovered by researchers from the Smithsonian Marine Station back in 2018. Scientists originally identified the beneficial bacteria on a coral colony that had remarkably and naturally resisted a severe local outbreak of stony coral tissue loss disease, commonly referred to as SCTLD. Recognizing the unique defense mechanism of this resilient organism, researchers isolated the bacteria to study its potential protective properties.
While scientists have previously tested the bacterial probiotic primarily on adult corals in controlled settings, a newly published study in the journal Frontiers in Marine Science expands on this research. The team has now investigated how this probiotic could limit disease spread in young corals and evaluated a specific compound produced by the bacteria known as tetrabromopyrrole, or TBP. By examining TBP, researchers hope to understand how it may protect entire coral colonies from succumbing to the deadly disease.
The dual nature of the compound has captured the attention of marine biologists studying the intricate chemical signaling within marine environments. Because TBP appears to act as a natural settlement cue for coral larvae, researchers believe there is an evolutionary and ecological logic to its protective qualities.
“If TBP is a natural settlement cue, and if bacteria that also produce this compound protect corals from disease, it makes sense that larvae would settle where those compounds are being produced,” Jennifer Sneed, a biologist at the Smithsonian Marine Station, said in a public statement. “More of them would survive to be able to recognize the compound.”
To rigorously test the efficacy of the compound in the field, researchers applied the probiotic to great star coral, scientifically known as Montastraea cavernosa, utilizing two distinct methodologies. The first approach involved injecting the probiotic directly into seawater contained within a weighted bag that was carefully placed around an individual coral colony. This technique allowed observers to test the effectiveness of a whole-colony treatment strategy. The second method utilized a concentrated paste applied directly to active, disease-related lesions on the coral surface. Following these applications, the research team meticulously monitored the corals and tested coral samples over an extensive monitoring period lasting two and a half years.
The long-term data revealed a stark contrast in effectiveness between the two application techniques. According to reports from Mongabay News, the corals treated via the whole-colony bagging method lost only about 7% of their tissue from the disease over the study period. In comparison, untreated control corals lost an alarming 35% of their tissue on average to SCTLD. These protective benefits persisted throughout the course of the research, with the probiotic treatment successfully slowing the rate of disease spread for two and a half years after the initial application.
Conversely, the localized paste application administered directly to individual lesions did not yield similarly successful results, proving significantly less effective at halting the broader progression of the disease across the colony.
Building upon these findings, the research team developed a practical protocol to apply the whole-colony probiotics via scuba diving. They also confirmed through rigorous observation that the deployment method and the bacterial treatment would not disrupt other healthy Caribbean coral species. This crucial safety verification paves the way for a potentially viable and safe SCTLD treatment protocol for full coral colonies in marine restoration efforts moving forward.
“While the whole-colony bagging method does involve more material transport by divers and more time for deployment and retrieval, its performance at treating SCTLD and promoting long-term resistance outweigh these costs and is therefore the recommended application method of those we tested for probiotic treatments such as the McH1–7 strain,” the study’s authors wrote in their published findings.
Despite the promising long-term results observed over the two-and-a-half-year monitoring window, the study’s authors have strongly emphasized that a significant amount of additional research remains necessary before this experimental approach can become a widely implemented clinical reality for reef management. They noted that future studies must be conducted to uncover supplementary treatments capable of addressing the wide array of diverse coral species that are concurrently affected by the deadly stony coral tissue loss disease across the wider Caribbean basin and Florida reef tract.
Researchers remain cautious, urging the conservation and scientific communities to view these developments as an encouraging step rather than an immediate, comprehensive solution to a complex ecological crisis.
“It’s important to understand that this is the very beginning,” Kelly Pitts, lead author of the study and a researcher at the Smithsonian Marine Station, told Mongabay News. “This is definitely not a cure-all, but we’re definitely moving in the right direction.”
