The World's Smallest Genome Just Got Smaller To make living organisms, a bundle of genes are needed. To make a human, for instance, you would need about 23,000. Now, scientists in Japan and the Unites States report new information about the minimum number of genes you need for life. And the number is remarkably small. Scientists used to think the number was around 300, but now researchers have found a bacterium that gets by with only 182 genes. The bacteria live inside tiny insects called psyllids. They posit that the bacterium is in the evolutionary process of becoming a part of the insect.
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The World's Smallest Genome Just Got Smaller

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The World's Smallest Genome Just Got Smaller

The World's Smallest Genome Just Got Smaller

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ROBERT SIEGEL, Host:

NPR's Joe Palca reports.

JOE PALCA, Host:

Nancy Moran of the University of Arizona studies these symbiotic bacteria. A few years ago, she got interested in a bacterium called carcinella.

NANCY MORAN: We did some sequencing to kind of characterize what kind of bacterium it was. And found that it was really truly bizarre. It had very extreme sequence features when you sequence the DNA.

PALCA: So to learn more about the bacterial genome she sent samples of carcinella off to a genome sequencing center in Yokohama, Japan. The results she got back were astonishing. As she reports in tomorrow's issue of the journal Science, carcinella is made up of only a 160,000 DNA letters and even more stunning, only a 182 genes.

MORAN: There's been a lot of studies, there's a lot of interest in sort of what are the minimal number of genes you need to make a cell and all the parts of the cell so that it will work, because a cell has to do certain things. It has to replicate the DNA. It has to make proteins. It has to do all of these processes that every cell has to do. And it takes different genes for those different jobs.

PALCA: Moran says prior to carcinella, no one had seen an independent cellular organism with fewer than about 400 genes. Eugene Conan at the National Center for Biotechnology Information says carcinella blows that figure out of the water.

EUGENE CONAN: It pushes considerably down that we ever imagined the minimum size of the genome of a cellular life form. And shows how little, actually, a cell needs to survive.

PALCA: A decade ago, Conan made the outrageous suggestion that a cell might get by on only 256 genes.

CONAN: Today, I would say that estimate should be roughly halved.

PALCA: Now, a symbiotic bacterium like carcinella can afford to give up some genes because it can rely on the cells of its hosts to supply its needs. But giving up too many genes can prompt a kind of bacterial identity crisis.

PATRICIA JOHNSON: It no longer can be independent at any level and becomes an integral part of the cell.

PALCA: For example, our cells have something in them called mitochondria. Mitochondria are known as the power plants inside cells. Johnson says mitochondria were once bacteria that gave up too many genes.

JOHNSON: Of course, these events occurred a very, very long time ago. And what's I think really, really extremely exciting about this new research is that we might be seeing this happen in real time.

PALCA: Joe Palca, NPR News, Washington.

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