In an article publishing Sept. 16 in the open-access journal PLOS Pathogens, Patrick Keeling and colleagues at the University of British Columbia in Canada describe investigations into an enigmatic group of coral-infecting microbes.
A further twist in the story came with the discovery that, despite lacking genes for photosystems or photosynthetic reaction centres, the Corallicolida genome includes genes for the four types of chlorophyll. The chlorophyll genes are expressed in Corallicolida cells and are subject to purifying natural selection — indications that they are still playing some role in the cell. Exactly what that role might be remains unclear, and much more research is needed to determine whether the Corallicolida are friends or foes to reef-building corals, the authors say.
“Coral reefs are an important marine habitat and well-studied biodiversity hotspot, so the fact that so many corals around the world are infected with an intracellular parasite that had hardly even been noticed is a testament to how little we know about microbial biodiversity,” Keeling adds. “For years these parasites were largely known only from hints buried in large-scale molecular sequence surveys, so hopefully by connecting a few dots to link up pictures, sequences, and host identification we can now start to look more deeply into how they infect, spread between hosts, and what effects they have on coral health.”
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