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The Teeniest Genome

People have about 3.2 billion basepairs in their genome encoding some 21,000 protein-coding genes, but other organisms have varying amounts as E. coli weighs in with about 4,200 protein-coding genes and a genome of 4.6 million base pairs, and others have far less, writes Carl Zimmer at The Loom.

Zimmer notes that he recently pointed out in his column at the New York Times that the tiniest known genome belonged to the microorganism Tremblaya that has 139,000 base pairs and 120 protein-codling genes.

But Tremblaya has lost its spot as the record-holder. Nasuia deltocephalinicola, Gordon Bennett and Nancy Moran report in Genome Biology and Evolution, contains 112,000 basepairs and 137 protein-coding genes — fewer basepairs, though more genes, than Tremblaya.

"What’s really striking about all these current and former record-holders for small genomes is that they all live in a single exotic ecological niche. Without exception, they can be found inside plant-feeding insects," Zimmer notes.

"The ancestors of Nasuia started out as free-living microbes that had genomes on par with E. coli," he later adds. "But once they got inside a host, they were able to lose DNA without paying a price."