Healthy Corals Carry Bacterial Communities Within
Researchers have found that bacterial communities living deep within the tissues of corals may help keep their coral hosts healthy.
Asian Scientist (Jul. 11, 2013) – Researchers have found the first direct evidence that Stylophora pistillata, a species of reef-building coral found throughout the Indian and western Pacific Oceans, harbors bacterial denizens deep within its tissues. These bacterial communities may help keep their coral hosts healthy.
Researchers have known for decades that most corals don’t like to live alone. Reef-building corals are known to have symbiotic, or mutually beneficial, relationships with single-celled algae.
More recent evidence has suggested that bacteria, fungi, and viruses are also part of the mix—especially a group of bacteria called Endozoicomonas, which has been associated with a number of coral species around the world. But scientists haven’t been able to pinpoint where exactly Endozoicomonas lives—in the coral’s tissues or on its surface layer—or what it does there.
In their study, published in Applied and Environmental Microbiology, the researchers gained access to the pristine coral reef colonies of the Red Sea. There, they used DNA-based techniques to uncover an abundance of Endozoicomonas genes associated with the coral Stylophora pistillata.
The team then created a DNA “probe”—a fragment of DNA designed to fit into the bacterium’s genetic code like a missing puzzle piece—that would light up when it connected with Endozoicomonas genes. Guided by the probe’s fluorescence, the researchers were able to spot Endozoicomonas living deep within the coral’s tissue.
“These weren’t single cells—they were living together in a clump, like a bunch of grapes on a stem,” said Amy Apprill, who co-directed the study.
“That was pretty exciting, because we had not thought about them living like this before.”
Although Endozoicomonas bacteria had previously been linked to coral colonies throughout the world’s oceans, as well as to some species of sponges and sea slugs, this study is the first to directly show the bacteria living within any marine animal. Now, the real mystery is what it’s doing there.
The researchers suspect the bacteria may help the coral recycle nutrients to stay healthy. They are currently designing new experiments to determine how the coral’s relationship with its bacterial companions works.
Future studies will also focus on searching the Endozoicomonas genetic code for bits of DNA that are associated with particular functions in other bacteria, and looking at other coral species to see if the bacteria lives inside them as well.
Understanding the bacteria’s relationship with Stylophora pistillata and other reef-building species could prove critical as corals face a growing number of threats to their health and survival.
“Corals are highly susceptible to the impacts of climate change, coastal development and overfishing,” said Apprill. “In order for scientists to predict the future success of corals, we need to understand their basic biology, including how their microorganisms may aid in keeping them healthy.”
Source: Woods Hole Oceanographic Institution; Photo: edanley/Flickr.
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