Symbiotic nitrogen-fixing cyanobacteria in corals

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Besides the symbiotic algae zooxanthellae, the Caribbean SPS coral Montastraea cavernosa also contains nitrogen-fixing cyanobacteria, according to the results of a new paper published today.

A team of biologists have reported in the journal Nature that the cyanoacteria within M. cavernosa are responsible for solar-stimulated orange-red fluorescence in the coral.

They claim that the fluorescence, which is spectrally similar to that produced by fluorescent proteins in corals, is created by phycoerythrin inside single-celled non-heterocystis cyanobacteria.

Like zooxanthellae, the cyanobacteria live inside the coral but fix nitrogen using a nitrogenase enzyme. The corals are found in a low-nitrogen environment and the researchers suggest that nitrogen fixation might be important source of nitrogen in the symbiotic association they have with the coral.

For more details read the paper: Lesser, MP. Mazel, CH., Gorbunov, MY and PG. Falkowski (2004) - Discovery of nitrogen fixing cyanobacteria in corals. Science, 2004. Aug 13; 305(5686) 997-1000.