Bacteria carrying viral genes trigger coral disease

Researchers identify the type of genes responsible for converting Vibrio coralliilyticus, a non-pathogenic coral bacterium into a pathogenic one that causes bleaching and death in reef-building corals. 

The bacterium needs to acquire key viral genes to become pathogenic. Such viral genes are part of a viral genome known as prophage that is integrated into the genome of a bacterium.

The same mechanism was observed in how Vibrio cholerae, a bacterium that causes cholera in humans, becomes pathogenic. 

The study, conducted by researchers from Australian Institute of Marine Science, Queensland, Australia, and King Abdullah University of Science and Technology (KAUST), Saudi Arabia, has identified that the prophage in V. coralliilyticus produces cholera-like toxins that potentially trigger diseases such as white syndrome disease in corals¹.

The scientists scanned the genomes of V. coralliilyticus from diseased and bleached corals from the Zanzibar coast, the Great Barrier Reef and Hawaii, as part of their study. 

At sea surface temperatures of 27 °C and above, the coral bacteria increases the production of cholera-like toxins, suggesting that pathogenicity islands and temperature may contribute to the emergence of pathogenic coral bacteria.

“This research shows that it is possible to search for prophages in coral bacteria, which could help indicate whether a disease or bleaching event is underway,” says Karen Weynberg, the lead author of the study. 

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