Diseased corals harbour bacteria

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Stony corals affected by the disease Rapid Tissue Necrosis contain larger numbers of pathogenic bacteria than healthy specimens, a new study has shown.

Pocillopora damicornis, a stony coral often kept in aquaria, is sometimes affected by the disease Rapid Tissue Necrosis (RTN), which causes the tissue to peel, but the precise cause was not previously known.

Now scientists from the Department of Marine Sciences at the Polytechnic University of Marche in Italy believe that a species of bacteria from the genus Vibrio may be responsible.

A paper due to be published in the journal Environmental Microbiology next month explains that one particular bacterium - Vibrio harveyi strain LB4 - is present at significantly higher levels in diseased Pocillopora damicornis than it is in healthy ones.

The team used epifluorescence microscopy - a scientific technique commonly used to detect and enumerate planktonic bacteria - to determine the abundance of bacteria and then grew cultures on a special type of agar plate.

They then undertook a molecular analysis to determine the type of bacteria present.

The authors said: "These results let us hypothesize that the RTN in stony corals can be an infectious disease associated to the presence of Vibrio harveyi. However, further studies are needed to validate the microbial origin of this pathology."

For more information see the paper: Luna GM, Biavasco F, Danovaro R (2007) - Bacteria associated with the rapid tissue necrosis of stony corals. Environ Microbiol. 2007 Jul;9(7):1851-7.