A Pox On Coral

Researchers have definitively linked a bacterium found in human waste to “white pox disease,” a disfiguring and lethal ailment that has helped put Caribbean elkhorn coral on the U.S. Endangered Species List. But some new sewage treatment plants may help stop the spread.

“These bacteria do not come from the ocean, they come from us,” says James W. Porter of the University of Georgia, a co-author of the study, which appears in PLoS ONE. “We are killing the goose that lays the golden egg, and we’ve got the smoking gun to prove it.”

Biologists have known since 2002 that the bacterium that was killing the coral was Serratia marcescens, a species also found in humans. But “we could only speculate that human waste was the source of the pathogen because the bacterium is also found in the waste of other animals,” says co-author Kathryn P. Sutherland of Rollins College.

To nail down the source of the pathogen, the research team collected and analyzed human samples from the wastewater treatment facility in Key West, Florida, and samples from several other animals, such as Key deer and seagulls. While Serratia marcescens was found in these other animals, genetic analyses showed that only the strain from human sewage matched the strain found in diseased corals on the reef. The final piece of the puzzle was showing, in carefully secured laboratory experiments, that the bacterium caused coral fragments to get the disease. “The strain caused disease in five days, so we now have definitive evidence that humans are a source,” Sutherland says.

This is the first time that a human disease has been shown to cause population declines of a marine invertebrate. Although the movement of pathogens from wildlife to humans is well documented (think West Nile Virus or bird flu), disease-causing microbes jumping from humans to marine invertebrates has never been shown before.

“Bacteria from humans kill corals—that’s the bad news,” says Porter. “But the good news is that we can solve this problem with advanced wastewater treatment facilities,” like one recently completed in Key West. The entire Florida Keys is now in the process of upgrading local wastewater treatment plants, and these measures should eliminate this source of the bacterium. David Malakoff | August 18, 2011

Source: Sutherland KP, Shaban S, Joyner JL, Porter JW, Lipp EK, 2011 Human Pathogen Shown to Cause Disease in the Threatened Eklhorn Coral Acropora palmata. PLoS ONE 6(8): e23468. doi:10.1371/journal.pone.0023468

Image James W. Porter, University of Georgia