Bacteria ID'd as Coral Killer

Armed with ample doses of ampicillin and tetracycline, antibiotics commonly prescribed by doctors and veterinarians, investigators of a recent experiment put the brakes on a deadly disease known to inflict horrific damage to animals.

The twist? In this scenario the patients weren’t humans, dogs, or horses, and the investigators weren’t physicians or veterinarians. Rather, the patients were coral and the treatment administrators were marine biologists.

A recently published study led by a Scripps scientist has pinpointed bacteria as the cause of “white band disease,” one of the world’s most damaging coral diseases (corals are animals rather than plants, as many believe). The disease contributed to a massive die-off of two of the most common shallow-water coral species in the Caribbean, wiping out up to 90 percent of these species on many reefs. The disease earned its name because its contagious death grip typically starts at the base of coral as a white band of dead tissue and works its way upwards, in certain cases at a couple of centimeters per day.

“In some cases the daily rate of white band disease growth can be greater than the annual growth rate of the species, so it can cause rapid mortality,” said David Kline, a Scripps alumnus who recently returned to the institution after working as a postdoctoral researcher at the University of Queensland in Australia.

Kline was lead author of the paper published in Nature Publishing Group’s Scientific Reports.

“Coral reefs are endangered all around the world from a number of causes, including climate change, pollution, and overfishing, but on top of that there’s also been these catastrophic diseases that have been globally causing huge levels of mortalities for corals,” said Kline. “We know almost nothing about these diseases, and we really need to put a massive effort into understanding them before they wipe out this really endangered ecosystem.”

White band disease helped decimate one of the most dominant shallow-water coral in the Caribbean (Acropora cervicornis) and made it the first and only coral species on the U.S. threatened and endangered list. But for such a prolific killer, surprisingly little is known about the disease and its causes. Prior to the study scientists weren’t sure if it spread through a virus, bacteria, or some unknown organism.

To find out, Kline and coauthor Steven Vollmer set up a novel experiment to test for candidates that might carry the disease. They retrieved living samples of white band disease near the Smithsonian Tropical Research Institute in Panama and developed their own “disease slurry,” applying the mixture to healthy coral.

Straining the slurry through various filters narrowed the suspects to bacteria, viruses, or both. To narrow the culprit’s identification, they treated the slurry with commonly used antibiotics. Ampicillin, used for decades to treat bacterial infections, knocked out 90 percent of the disease, clearly fingering bacteria as the cause of white band disease.

Kline is continuing the research by seeking to identify the type of bacteria that causes white band disease.

The research was funded by a Smithsonian Marine Science Network postdoctoral fellowship.

-- Mario C. Aguilera