by ANDY COGHLAN
An evolutionary halfway house IMAGE/Dr Niculina Musat and Dr Cristina Moraru/MPI Bremen, Germany
Every so often biology unveils an organism that demonstrates evolution in action. More rarely, it offers up a twofer. Deep in the world’s oceans, biologists have found a species of cyanobacterium that may be midway the process of becoming an organelle within a species of algae.
Candidatus Atelocyanobacterium thalassa is a cyanobacterium like no other. Its streamlined genome shows that it excels at grabbing nitrogen from the water and turning it into a form (ammonium) that organisms can handle. But it lacks the genes for photosynthesis that other marine cyanobacteria use to generate their food. Unusually for a cyanobacterium, it must rely on another organism for its food.
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