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Remnants of an algae’s distant past

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Some algae such as Guillardia theta have a main nucleus and a second tiny nucleus called a nucleomorph—a remnant of the algae's distant past.

Algal efficiency. The nucleomorph of Guillardia theta, surrounded here by other algal species (all in false colors) has an extremely dense genome.

When G. theta came into being millions of years ago, single-celled algae swallowed primeval plant cells, which were in turn swallowed by larger, single-celled organisms. This created microscopic Russian dolls. In G. theta and some other algae, the nuclei or 'nucleomorphs' of the swallowed cells have remained viable as independent nuclei.

In 2001, researchers sequenced the nucleomorph of G. theta. With some 500 genes distributed among 551,000 base pairs, the nucleomorph has one of the densest non-bacterial genomes known to date.

Birgit Reinert

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