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Life Inside Carpenter Ants
By Kate Dalke

You’ve got to give a little, take a little. That’s the attitude of a tiny bacterium called Blochmannia floridanus, which makes its home inside the abdomen of carpenter ants.

Black carpenter ant.

The ant and the microbe live in a seemingly blissful state of communion. B. floridanus provides essential nutrients to the ant, and the ant supplies a constant environment of vitamins and proteins for the bacterium.

Now, researchers have sequenced the genome of B. floridanus, and compared it with the already completed genomes of four other symbiotic bacteria that live inside insects.

The other bacteria are Wigglesworthia glossinidia, which lives in the blood-sucking tetse fly, and three strains of Buchnera apidicola, which live inside the stomachs of aphids, small soft-bodied insects that feed on plants.

All the bacteria, including B. floridanus, have co-evolved over millions of years alongside their insect hosts, and are completely dependent on the insects for life.

One feature stands out among the handful of genomes of insect-dependent microbes: their reduced genomes. In each case, bacterial genes that code for essential proteins have been destroyed or removed, and their host insect provides these proteins.

These reduced genomes could help researchers identify the smallest number of genes that is essential for life—what scientists refer to as the minimal genome. Starting with a small genome makes it easier to pinpoint a core set of genes that are necessary for cells to function.

Isolating the bacterium’s DNA was the hardest part of the project. B. floridanus cannot grow by itself in the laboratory, so the researchers had to extract its DNA from ants.

B. floridanus lives inside cells surrounding the stomach of carpenter ants. The researchers crushed the abdomens of about 100 ants, and then took rigorous steps to filter out any ant DNA or debris from the sample.

“The most difficult stage in sequencing was actually the first one,” says Andrés Moya, who led the sequencing project at the Institut Cavanilles de Biodiversitat at the Universitat de València in Spain.

The genome sequence of B. floridanus is a triumph for Moya and his colleagues, as well as for Spain, which does not have any large-scale sequencing centers. It is only the second genome completely sequenced in Spain; the sequence of a strain of Buchnera was the first, in January 2003.

—Related Articles—

Another Minimal Genome: Microbe Needs Just 271 Genes

Inside Insects, Life is Unchanged for 50 Million Years

Wigglesworthia Wiggles Into the World of Sequenced Genomes

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Gil, R. et al. The genome sequence of Blochmannia floridanus: Comparative analysis of reduced genomes. Proceedings of the National Academy of Sciences USA 100, 9388-9393 (August 5, 2003).

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